The Ultimate 88/98 Toolbox

[Devs93]

Copied and pasted this from another site tons of awsome info
I’ve been on the forum long enough to notice the same questions popping up again and again. Although the forum has a search feature, it is often easier to just ask your question. That's what the forum is for. Well to lessen repeat questions, I've attempted to gather together some great discussions on TBI- and Vortec-related performance topics into one big post – perhaps the ultimate post. I have not limited myself to this board and have included very useful discussions/info from other websites. I have used a running FAQ-type commentary to minimize reading through a ton of posts and so that I can share with you my experiences and expertise. Hopefully, this thread will serve as an important resource for those of you who are new to OBS trucks and serve as future reference for the FSC “old timers”. Feel free to offer suggestions or add your own Q/A entries to the appropriately entitled...

ULTIMATE 88-98 OBS PERFORMANCE TOOLBOX


What is TBI?
TBI stands for throttle body injection. This was one of the first mass-produced fuel injection systems on GM trucks starting in 1987 for the final year of the square box body style. GM introduced a redesigned body style the following year in 1988, which would last 11 years from 1988 to 1998. TBI-equiped motors included the 4.3L V6, 5.0L, 5.7L and 7.4L engines. The 7.4L version aptly resided in 454SS trucks and production ran from 1990-1993. The 5.7L TBI engines were produced from 1987 to 1995, with power levels that ranged from 185-210hp. These pre-Vortec engines used hydraulic non-roller camshafts.


What’s a Vortec engine?
In 1996, GM introduced the 5.0L and 5.7L Vortec engines were that included several key enhancements: hydraulic roller camshaft, new higher flow Vortec cylinder heads, central sequential fuel injection (CSFI), OBDII, etc. These enhancements allowed the 5.7L Vortec engine to produce 250 hp and 320 lbs-ft of torque. Production of these engines ran until 1998 when GM redesigned the Chevy and GMC trucks for the 1999 model year, ending the smooth body style now referred to as the old body style (OBS).


Are there any cheap ways to make more power and get better fuel economy?
Well it depends on how much of the work you can do yourself. There are free or relatively cheap mods for sure, like the infamous reverse air lid trick on TBI engines, the ultimate TBI mods, and making your own AFPR for your TBI engine. You can also learn how to burn your own PROMs for a small investment that will pay you back huge as you keep upgrading your motor with better fuel economy and power. But unfortunately, more power requires a significant investment in time and money. Speed costs money…How fast do you want to go?

Better fuel economy can come with more power. How? Because it takes less throttle to get going and less pedal to keep you going. On the highway, you’ll especially notice the difference when your engine doesn’t have to downshift in order to get up hills. It is power that you can feel and it will save you money at the pump. The other factor is driving-style. Light throttle saves you money at the pump. Not always easy, but that’s the key to saving money on fuel costs. Let’s be honest here. V8 engines, despite their “advanced” fuel injection, are only capable of about 17-18 miles per gallon on the highway. If you wanted fuel economy, you would have bought a hybrid car instead.


What should be the first thing I do to my TBI/Vortec engine?
The first thing you should do to your engine is to make sure it has a complete tune up and is in proper running condition. This means replacement of the spark plugs and wires along with a new distributor cap, and rotor. The TBI or throttle body unit should also be cleaned thoroughly. This requires taking it off and cleaning all of the small passages that run along the bottom side of it. Cleaning or replacing the PVC valve is also crucial. You will also want to check your serpentine belt and coolant and vacuum hoses. They get old and crack and break down over time and this would be a good time to replace them. Finally, you will want to check your timing. The factory setting for the L05 (TBI) 5.7L engine is 0* but check your engine’s emission sticker under the hood for the factory timing setting for your truck. You can advance the base timing if you want, but timing is mainly controlled by the engine’s computer. A custom chip will add more timing under the curve to improve low RPM torque, so adjusting the base timing is pointless. You may have to run a higher octane fuel though so you will have to consider that. After your truck has received a full tune up you can start to consider your first modifications.


What is involved in a performance tune-up? What are some regular maintenance items to replace?
A complete tune-up includes: new air filter (cleaned reusable filter), new distributor cap/rotor, new spark plugs set at the appropriate gap, test and replace faulty spark plug wires, check timing, check and/or replace PCV valve, check and replace faulty vacuum hoses, check coolant level, oil/oil filter change, check transmission fluid level, check steering pump and brake fluid levels, check windshield washer fluid, check and readjust TV transmission cable (pre-93 trucks), remove slack from throttle linkage, clean terminals on battery.

Some common replacement items in general and preventative maintenance: Fuel filter, O2 sensor(s) (replace after 65,000-80,000 miles), PVC valve, belts, wiper blades.


I want to clean my IAC because I’ve heard that it can affect engine idle. How can I do this?
The quick way: remove the IAC and lightly spray carb cleaner on it and inside the chamber. Wipe the residue off with a shop towel. Reinstall.

The detailed step-by-step, careful approach:
1). Remove the IAC. It can be found on the pass side of the TBI.

2). After you have done so, reconnect the IAC connector and place a bag or towel around the IAC so the pintle doest go flying off. Once this is done, jumper pins 'A' + 'B' in the ALDL connector. Once jumpered, turn the key to the ON position, but don't start the car. The ecm will eject the IAC pintle. Turn off the ignition and remove the IAC and its components.

3). Next step is to clean the parts. I like using lighterfluid or naphtha. Cleans and leaves no unpleasant odor once it evaporates. Use a toothbrush to remove all the carbon deposits from the guide, spring, and the threads on the pintle shaft. Once dry lightly coat the pintle shaft and guide with a light grease or oil.

4). Reassemble. Place the spring over the pintle and place the pintle shaft in the guide slot in the IAC. It wont just go in as there is an armature with gear teeth on it. Screw the IAC pintle in until the guide slots on the pintle shaft just meet up with the guides in the IAC main body. From there gently rock the IAC pintle back and fourth while applying light pressure until the pintle gets partially back into the IAC.

5.) Reinstall the IAC. Screw it in by hand and if you feel any sort of resistance, STOP!!! The pintle has bottomed out. Reconnect the IAC and pull the jumper out of the ALDL if you have not yet done so. Lightly depress the gas pedal and start the car. Let it run for about 30 secs and shut down. Hand tighten the IAC and add about 1/16 additional turn is about all that's necessary. And you’re done. The vehicle is ready for use.

[Devs93]

How do I adjust my TPS?
On TBI engines, the TPS is not adjustable. Just leave it alone. You can test it for proper operation using a volt meter, but there is no need to adjust it. Here’s a link that will help you to test your TPS using a digital volt meter: http://autorepair.about.com/cs/faqs/l/aa042603a_1.htm. It also includes instructions on how to test other sensors for proper operation and may help to fix common engine problems.


Will using higher octane fuel add power?
No. If your 350 TBI is stock and running the stock base timing setting of 0* advanced, then there is no need to run higher than 87. Even with 0* you could possibly still hear knock. This could be caused by excess carbon deposits that are creating detonation usually found in high mileage motors. Seafoam top engine cleaner or equivalent (GM top engine cleaner) can be used to remove these deposits and prevent detonation. Higher octane fuel may be required for engines that are running high compression ratios or advanced timing curves from a custom chip or tune. Running higher octane fuel than is needed for your application will not clean your engine or add power to it. In some cases it may actually decrease power because of an incomplete combustion.


Now that my engine has a tune up, what areas should I start to mod/upgrade?
An extremely popular first mod is removing the stock air intake snorkel assembly and replacing it with an open air element or cold air intake (CAI) kit from K&N, AirRaid, etc. An open element will sit flat on top of your TBI unit and allow you to remove the spacer ring that surrounds the perimeter of the top of your TBI unit. Before you look into serious mods like heads and a cam you need to address the other weak points of the truck, such as the exhaust system and fuel system. A complete exhaust upgrade from the exhaust ports back should be installed as the first major mod to take the full advantage of future upgrades. Also, the stock fuel pump will not be able to effectively support the power your motor will make with a new cam and heads. Installing a larger fuel pump will not affect the fuel pressure of your current setup since the pressure is modulated by the fuel pressure regulator, not the pump. An adjustable fuel pressure regulator and a fuel gauge should be added to adjust fuel to match your power upgrades as you go along. Lastly, you will want a performance chip/tune. The best approach is burn your own chips, but there is a steep learning curve. The next best option is to have tuners such as Wester’s Garage, Wait4Me, TBI Chips, etc, burn you a custom PROM for your application, particularly if you’ve changed the displacement, heads, and/or cam on your engine. On a mostly stock engine, chips and tunes from Jet Performance, Hypertech, etc. will work fine.


How do I do the ultimate TBI mods and are they worth it?
The ultimate TBI mods are a set of modifications that improve the airflow and fuel into your engine. They include: removing the ridge on the injector side of the TB unit, shaving the throttle shafts, installing an injector pod spacer. There are two great tech articles on how to do this below and they are pretty straight forward once you have a grinder and TBI unit in your hands. It will improve airflow by about 5%, but more importantly unshrouds the injectors for a cleaner air entry + fuel atomization. This added flow will help at higher RPMs. Companies like CFMTech and XtremeFI also manufacturer TB with larger than stock 46mm holes (48mm and 50mm). These units already include the ultimate TBI mods mentioned performed on the TB.

Ultimate TBI mods instructions: http://www.thirdgen.org/ultimatetbi and http://www.thirdgen.org/ultimatetbi2
Pics of the ultimate TBI mods: http://www.thirdgen.org/techboard/tb...owing-tbi.html


Will a larger TB make more power?
IMO this should be your last upgrade. I’ll say it one more time: most people overestimate the CFM requirements of their engine. For a more accurate estimate: use the Wallace Racing CFM calculator: http://www.wallaceracing.com/intakecfm.php. I like it because it also takes into account the type of intake manifold. Engine CFM requirements highly depend on the Volumetric Efficiency (VE) of your engine at red line. It automatically calculates the compensatory 120% to 150% of the engine's base requirement using the dual plane intake. If you were to use a single plane intake (yes one exists - the Edelbrock MPFI unit is a single plane design), the percentage over the engine's base CFM requirement is between 110%-130%. Most factory engines are between 65-75% VE at redline. On a mildly upgraded 350 engine (i.e. headers, exhaust, chip) with stock heads and cam, the VE hits about 72%. If you were to change cams, you're looking at about 78% VE. Change heads and cam, about 85-88% VE.

Stock TB cfm on a 350 engine is 490 cfm at 1.5inHg. Redline on the stock engine (or mine at least) is 4500-4750 RPM. Like I said before, the stock engine's VE is about 66%. Input the numbers into the calculator and what do you get: 381 to 476 cfm. So that's why the engineers at GM chose the size of TB that they did. Now let's now say you've changed the cam plus all the other performance goodies, redline now at 5000 RPM, stock heads, VE now at 78%: 474 to 592 cfm required. You could still use the stock TB easily with no major bottleneck in power. Ultimate TB mods would give you 520 cfm. Even with a cam change and other performance goodies, the stock TB is still pretty decent. You could upgrade to the CFM-Tech unit rated at 590-620 cfm if you wanted to.

What if you changed heads/cam now and redline at 5600 RPM, VE now at 88%: You'd need 613 to 766 cfm. The CFM-Tech TB would work, but the larger 50mm TB would be better. It's rated at 690-750cfm, depending if you believe the upper figure quoted by XtremeFI or not. The 454 TB (also 50mm) is rated at 670 cfm at 1.5inHg w/o the injector pod according to airdeano's tests. I'd tend to believe airdeano's numbers more because they're pretty bang on: http://www.fullsizechevy.com/forums/...d.php?t=145234.

A 383, stock heads, with cam, Redline at 5000 RPM, VE again at 78%: 519 to 648 cfm. Either the CFM-Tech or XtremeFI TB would work. The stock TB even with the ultimate TBI mods (520 cfm) would be too small IMO.

The bottom line is: calculate the CFM requirements of your particular engine. Most likely, you won’t need to buy a larger TB unless you’ve made extensive upgrades to your engine. The ultimate TBI mods are relatively easy to do yourself and will increase your TB airflow to about 520 cfm. More than enough to support your performance upgrades. (Note that the required cfm of your engine has nothing to do with hp!!)


What is a TBI spacer and does it add power?
A TBI spacer is just what it sounds like. It is a piece of plastic, wood, phenolic resin, or aluminum that bolts in between the TBI unit and intake manifold. It helps increase the intake manifold plenum size and is designed to add power. It also acts as a thermal insulator between the TBI unit and intake manifold. Resin and plastic materials may be more effective than aluminum and since they will not conduct as much heat into the TBI unit. There are two paper gaskets between the TB and the intake manifold so you be the judge. Most people claim that they have improved throttle response and mid-range torque after installing their spacer. A TBI spacer usually requires a little tweaking of the throttle brackets and TV cables (for pre-93 trannys) to keep it from pulling the throttle open. Make sure you properly adjust your TV cable. Failure to do so could result in transmission failure. Any service manual has an instruct set on how to properly adjust your cable. An on-line service manual is available from Autozone’s website: http://autozone.com/servlet/UiBroker...Parameters=005

Also, keep in mind that if you upgrade to a larger TB, it is a good idea to have your throttle body spacer and intake manifold machined to match your intake tract.


What is an injector pod spacer and do they add power?
An injector pod spacer is a plastic spacer that raises your injector pod up 1/4" to unshroud the injectors for better air and fuel delivery. They can be found on ebay and are also sold by Jegs and Summit Racing. This mod is considered a component of the ultimate TBI upgrade. Do they add power? No dyno tests have ever proved it but when combined with the Ultimate TBI mods, your truck engine will gain both fuel economy and power: http://www.cfm-tech.com/trucksarticle.htm


How much power can my stock fuel pump support?
The answer is not much. On the typical 350 TBI engine with an AFPR, up to 240 hp. Past this, and you need larger injectors, more fuel pressure, and/or a larger fuel pump. A high flow unit will supply enough power to your TBI system no matter what mods you go with. Popular choices include, stock GM TPI pumps, Walbro 190lph and 255lph, and the Holley 255lph. Each of these pumps can support gobs of power but will work safely with your TBI set-up because your fuel pressure regulator will keep the fuel entering into your TBI unit where it needs to be. For Vortec engines, fuel injectors are rated at 19#/hr at 42.5 psi, but the stock fuel pressure is actually at 60 psi (22-23 #/hr). Max hp is about 330 hp because of the limitations of the fuel injectors. There is some discussion that some Vortec injectors make be underrated and may flow up to 28#/hr at 60 psi. This would support around 400 hp. Unfortunately, there are no larger replacement fuel injectors for Vortec engines or direct-fit AFPR that can boost fuel pressures to support more hp. Some Vortec owners have gone so far as to replacement their Vortec induction with the marine version, which uses 24#/hr fuel injectors. This way, the induction system won’t be the bottleneck in making big power.

[Devs93]

What is an adjustable fuel pressure regulator, who makes them, and are they worth it?
A fuel pressure regulator does just as it sounds. It limits the amount of fuel that enters into your injector pod. There is no set value that came from the factory, but most are setup between 11-13 psi. Adding performance mods to your engine may require that you adjust the fuel pressure a bit to allow more fuel in. You can make the existing TBI fuel pressure regulator adjustable at the following link: http://www.thirdgen.org/tbi-afpr. Jet Performance also makes a replacement unit. If you want one that varies with RPM you will need to look into the GM vacuum adjustable regulator. This regulator changes based on a vacuum source and will rise as RPM does. It is still adjustable so that you can tune down the pressure at idle to avoid running rich, yet have enough pressure at wide open throttle to avoid going lean. To hook up a fuel gauge, you'll need one of these: http://marine-performance-parts.com/...843505774.aspx. Or you can hook up an external AFPR like this: http://www.fullsizechevy.com/forums/...-tbi-pics.html.


What are the major troublesome areas to overcome in TBI engines to make awesome power? In Vortec engines?
TBI engines (1988-1995): Quite a few, unfortunately.

Airflow: The TB is relatively small at 490cfm at 1.5inHg. The ultimate TBI mods can be performed to raise this to 520 cfm. If you’re changing heads, cam, displacement, or adding a supercharger, this won’t cut it and you need more air. Larger TB that are direct replacements for your stock TB are made by CFM-Tech and Turbo City (590-620 CFM), or XtremeFI (750 cfm). The 454 TB can also be used (rated at 670 cfm at 1.5inHg), but there are some incompatibility issues with the IAC (Idle air control) and TPS (throttle position) sensors. These issues can be overcome by splicing the 454-style TPS and IAC sensor wires to the wires from the small block TPS/IAC. Keep in mind that all small block TBs aren’t the same. There are slight changes in design in the production years from 1988-1995. Ask for a TB from your model year or send them your original to be modified. Holley also makes a replacement TB (750 cfm) with larger 68#/hr injectors. I think it gets a bad reputation because it doesn’t improve the performance (or sometimes worsens the performance on TBI engines). If you're using the Holley TB, you need a custom chip to make it work properly for your application (i.e. change the fuel injector constant, VE tuning, etc.). The computer thinks it still has the smaller injectors with less air going into the engine. The VE tables need to be re-calibrated via the chip to make this unit a performer. Something Holley doesn’t tell you.

Heads: The L05 5.7L head is a swirl port design, meaning that there are these ridges in the intake runner and under the valves to promote better fuel atomization and improve low RPM torque. The truth is it works – at low RPM (3500 and under). Problem is most people are looking for gains in top end hp and these heads are at a mechanical disadvantage to provide adequate airflow for high RPM power. The solution: either port them or replace them. Popular replacement options include using Vortec heads or aftermarket cylinder heads. Because of their centerbolt head design, they are few options for aftermarket heads and some are more expensive than others. The poorest performer IMO is the Edelbrock centerbolt head, but it seems to be the most well-known head for TBI engines. There are also the Torquer S/R from World Castings, AFR 180 or AFR 195, Canfield heads, Pro Topline heads from Racing Head Services (RHS), Patriot heads, and Trick Flow heads. There are three factors that you need to decide which head is right for you: head airflow characteristics (the higher the better), intake runner size (max should be 195cc for a 350 otherwise will start to dramatically lose low speed torque characteristics), and combustion chamber (stock 350 is 64cc for roughly a 9.3:1 compression ratio). The new Eliminator AFR 195 head is arguably the best performing head with huge airflow numbers to generate tons of hp and now available in 64cc combustion chamber (both CNC and non-CNC versions). I chose the Trick Flow 195 heads for my engine: reasonably priced, good airflow, 195cc intake runner, and a 62cc combustion chamber. So make sure you remember these important factors when choosing heads for your engine.

Camshaft: one word - wimpy. Less than 0.400” lift and small (172/180 at 0.050"), it is just a horrible design for making good power. Great for towing and low speed torque, but newer camshaft designs today can improve your low speed torque and provide major hp increases when combined with other performance upgrades. Please read later in the thread on how to choose the right camshaft for your truck. Depending on your engine combination and whether you’ve changed heads or not, there are several performance options that are available.

exhaust: There were many different styles of exhaust from 1988-1995. All were a 2-into-1 design using a catalytic converter. Older designs used AIR injection with a smog pump and a less efficient pancake-style (pellet) catalytic converter. It is unclear when monolithic (high flow) converters were introduced. Some say in 1996 with the introduction of the Vortec engine. I just took the stock catalytic converter off my 1994 350 truck and it was a monolithic design and replaced it with a high flow unit from MagnaFlow. Don’t know if the stock one is considered high flow or not, but it was pretty plugged so any comparisons would be meaningless. What do you want for exhaust? Replace everything!! Now with what? You have several options again. The best exhaust system IMO is long tube headers with 2.5” true dual exhaust (2 mufflers, 2 catalytic converters, etc.). Another option is shorty style headers (direct-fit), stock or aftermarket y-pipe, 3” intermediate pipe. If you choose not to run a catalytic converter, this combo can be used to make good hp if you’ve changed heads/cam on your engine. On a TBI engine with stock heads and cam, running a 3” catalytic converter WILL NOT greatly limit the hp potential of your motor. A 3” high flow cat can roughly flow 360 cfm of air. I know it doesn’t sound like a lot, but most people overestimate the required air for their engine. A stock 350 TBI engine with performance exhaust only needs 355-444 cfm of air with a 4500 RPM redline and 65% VE. A section on the effect of larger TB is listed earlier in this thread.

Vortec engines (1996-1998):

Fuel injectors/Intake manifold: The fuel injectors on Vortec engines cannot be replaced with standard aftermarket injectors (stock is 22-23#/hr at 60 psi). As far as I know, there is no direct-fit AFPR that is available for their engines. Perhaps the stock one can be modified or a universal AFPR can be used, but it will require some creativity and ingenuity. In fact, Vortec Stroker has a 383 using the stock Vortec induction making 400 hp, so it is possible to make big power using this setup: http://www.fullsizechevy.com/forums/...ad.php?t=83738. I suspect that his BSCF engine rating used for supported hp calculations is under the standard 0.5. Airflow is the biggest bottleneck in the Vortec system since the fuel injector poppets are in the intake tract. A direct bolt-on marine version of the Vortec induction system is available that uses larger 24#/hr fuel injectors that are mounted outside of the intact tract and allows better performance up to 5800 RPM. This is one way to get around this potential bottleneck. Another way is to replace the whole induction unit with another MPFI system, like the Holley Stealth Ram or GM’s RamJet.

[Devs93]

Heads: The Vortec heads are great heads, but there are not without their problems. The valve springs only support up to 0.450-0.470” lift camshafts depending on the sources you read. Since the Vortec engines use hydraulic roller cams, it would be silly not to upgrade the springs in order to take advantage of today’s high lift roller camshaft designs with lift in excess of 0.500”. Chevy High Performance has an article on upgrading your springs here: http://www.chevyhiperformance.com/te...ort/index.html. In this example, the valve seats are machined and larger springs are installed. Springs are also available that will increase your valve lift without machining the valve seats. Comp Cams Beehive 26915 or the Beehive 26918 springs can be used as direct replacements without machining the heads and will allow up to 0.550” lift. Contact Comp Cams or Crane Cams and ask them directly for which springs they’d recommend if you are unsure. Here’s another article on everything you wanted to know on Vortec heads: http://www.chevyhiperformance.com/ho...458/index.html. The ideal aftermarket head for the Vortec engine IMO is the Edelbrock Etec head. A serious performer for the money.

Camshaft: better than a TBI engine and it’s a roller camshaft, so it’s pretty good, right? Nope. If you want to make big power increases, you have to change the camshaft. This bottleneck is intertwined with the previous two bottlenecks. With more fuel and heads that support high lift, a 400+ hp engine is entirely possible. Again, the combination of parts selection is the key here. Installing a camshaft in a stock Vortec engine is not going to perform miracles, but will improve performance. Please read later in the thread on how to choose the right camshaft for your truck.


I want to add a supercharger to my engine. How do I do that and what are my choices?
First off, supercharger kits are mainly designed and calibrated for the stock engine. It will tolerate mild performance upgrades such as headers and low-restriction exhaust systems, but if you want to start changing cylinder heads and camshafts, you’re going to need to find someone to custom tune your engine or do it yourself. Be prepared to troubleshoot A LOT when adding a supercharger to your engine. It is not as easy as it seems, although the power gains (and particularly the torque gains) are outstanding and well worth the efforts. Depending on your power output, you may need to upgrade the transmission as well, so keep this in mind before investing in a supercharger kit.

TBI engines:
There are three quality manufacturers that I know of: Whipple Industries, Weiand, and ATI ProCharger. Each has their selling points. The Weiand emissions-legal kit is the least expensive at under $3000, but hood space is definitely an issue since the TB sits on top of the unit. There is also a super-cheap $1500 non-emissions kit available that uses a carb setup. Here is an article from someone who has done this to their 350 engine: http://www.thirdgen.org/weiand142install. Definitely needs a cowl induction hood and you may need to modify it to make room for the air filter. A shorter open element filter with K&N Xtreme filter lid may work, but since I don’t have one I wouldn’t know. It uses a 144 roots-style supercharger that adds between 25-30% additional hp/torque. The potential for more boost is possible, but it is limited by the enormous heat that is generated by the roots-style blower. The Whipple supercharger is popular because of its efficiency and low-RPM performance, adding 40-45% more power. Full boost is achieved at low RPMs making this an excellent choice for trucks that need to tow. The ATI ProCharger is the only centrifugal supercharger available from a major company. It is intercooled and therefore provides 8-9 pounds of boost (2-3 more than the Whipple supercharger). Power is improved by 65%, but it is mainly in the upper RPMS. Don’t count on this supercharger to improve your towing capacity significantly around town. On the highway, sure, but you won’t have the torque that the Whipple unit provided down low.

Vortec engines:
In addition to Whipple and ATI mentioned above, there is also Vortec Engineering and Powerdyne, both of which are centrifugal supercharger designs. These superchargers will add up to 50% more power.


Will roller rockers or higher ratio rockers improve power?
Yes and maybe. Roller rockers will reduce frictional parasitic losses on the valvetrain components to free up a few ponies. Higher ratio rockers have their applications: useful on stock cams to improve lift and therefore flow more air, maximize the airflow potential of aftermarket heads and camshafts. They also have their drawbacks: Stock TBI heads have low flow potential and using higher ratio rockers with an aftermarket camshaft may not improve power over the aftermarket camshaft alone since the maximum airflow of the heads have been reached; Vortec heads only allow valve lift up to 0.470” and installing higher ratio rockers may surpass the valve lift depending if you’re running the stock cam or not. With the stock cam, 1.6 ratio rockers are dangerously close to that upper limit, but still under. So how do I decide? Guess it depends on your engine combination and what your future upgrade plans are. Keep in mind that higher ratio rockers will increase the advertised duration of your cam. Comp Cams now has a new XFI series of camshafts designed to use their beehive springs and 1.6 ratio rockers. There are both hydraulic and hydraulic roller versions of the XFI cam. The advantage is that you precisely know the advertised duration of the camshaft with its higher lift potential.


How do I choose the right camshaft for my engine?
Oh man, probably the most common question on this forum and the one with the most answers. You can get really technical answers or very simple rule-of-thumb answers. The reason there are so many different answers (and camshafts for that matter) is because it highly depends on your engine and transmission combination and how you plan on using your truck (towing, racing, daily driver, etc.) Transmission? What does that have to do with it? Well first of all, you can choose slightly more duration with a standard transmission because you can essentially adjust the stall of the engine when starting out from a stop. Automatic transmissions don’t have that luxury and usually stall at about 1100-1300 RPM. If you choose a high duration cam with a narrow LSA (lobe separation angle) for a lopey powerful engine, you’ll gain hp up top, but lose torque down low. More importantly, installing a large duration cam in TBI engines with their torque-producing, low RPM cylinder heads is a major mismatch. The heads will not be able to support the power above 4000 RPM where the cam will be making its most power. The results = a dog of an engine down low and on the high end.

Here are my recommendations for cam choices based on the engine combo you have (all of which need custom chips or performance tuning to work properly and maintain fuel economy. This is required for ANY camshaft upgrade.)

TBI 5.7L with stock heads, stock or 2000 RPM stall torque converter: Duration at 0.050” lift 206/216 with LSA 112. The Crane cam 113904 is my top choice, but as long at you stick to intake duration under 206 degrees, you’ll have a safe computer-friendly cam with gobs of power 4500 RPM and lower. Good for towing and performance applications and good all-round choice. Power level maxes out at 280-300hp.

TBI 5.7L with after market heads, stock converter: Highest lift possible is the key here to take full advantage of your performance heads. My choice would be Comp’s 260 XFI hydraulic camshaft, 216/223, 0.499”/0.492” lift with 1.6 ratio rockers or the Comp Cams XE256H, 212/218, 0.479"/0.486" with 1.6 ratio rockers. Expected power levels will be around 320-345 hp. The Comp XE256H is a perfect cam swap for upgraded Vortec heads if you run 1.5 rockers (0.449"/0.456") that won't require any modifications to the valve springs.

TBI 5.7L with after market heads, 2500 RPM stall converter, 3.42 or higher rear end: Comp’s Xtreme Energy Computer Controlled XE262H with 1.6 rockers (218/224 at 0.050” lift, 0.510”/0.517”) or "XFI" 268 Hydraulic Flat Tappet Camshaft, 224/231, lift 0.520"/0.515" w/1.6 Rockers if you want to push it. You WILL need a higher stall converter with these cams. Dyno simulations of these combos produce 365+ hp at 5500 RPM. Yes, from a TBI. Tuning and proper fuel deliver is a must.

Vortec 5.7L engine without spring upgrade: Crane’s 109815, 204/214, 0.429”/0.452” lift.

Vortec 5.7L with spring upgrade: Comp cams Xtreme Energy Computer Controlled XR254HR (206/212, 0.480”/0.488”) or Comp cams Xtreme Energy Computer Controlled XR264HR (212/218, 0.488”/0.495” lift).

Vortec 5.7L with performance Vortec heads (i.e. Edelbrock 170 E-Tech heads with max valve lift of 0.575”) and fuel/induction system upgrades: Comp’s 260 or 268 XFI hydraulic roller series, 210/218 or 218/224 at 0.050” lift, 0.560”/0.555” or 0.570”/0.565” lift, LSA 113, 1.6 rockers. You could even go with 280 XFI cam with a 2500 stall torque converter. How does 400+ hp sound?

[Devs93]

Can I install a hydraulic roller camshaft in my TBI engine? What do I need to know?
Yes, the TBI engine blocks have all the provisions for hydraulic rollers, including the bosses for the spider. Unfortunately, they are not pre-drilled. Therefore, you should disassemble the engine first to avoid getting metal shavings in your engine. There are two terminologies that you have to watch out for here: Retrofit roller cams are for pre-87 blocks: OEM roller cams are for 87 and later blocks. The best way to convert to a hydraulic roller is to buy a kit available from camshaft companies like Comp Cams (K-kit) that includes almost all the parts you need for the swap. The only additional parts needed are the spider, retainer plate, and the roller rocker arms. Total cost however is about $1000.
Read the following article for more info on installing a roller camshaft: http://www.chevyhiperformance.com/te...ler/index.html

An except from the article: “One of the more budget-oriented conversion kits from GM Performance Parts is the Hot hydraulic-roller cam. This particular cam was originally designed for the LT1 small-block and used 1.6 roller rockers. ... This is a great cam; in a 355ci small-block with Vortec heads and a GM Performance Parts dual-plane intake, it made 412 hp and 422 lb-ft of torque with 9.75:1 compression.”


Is there any way to predict what kind of hp I’d expect from my performance upgrades?
You bet. I did a series of common engine upgrades using the stock TBI engine to illustrate the utility of dyno simulation software. Here’s a link to the thread: http://www.fullsizechevy.com/forums/...d.php?t=194581. Engine sim software is an invaluable resource in helping to choose the right camshaft or the right performance heads. You can also couple your engine with the Drag sim software to see how your engine upgrades will perform on the street. You can try out different rear ends, transmissions, or higher stall torque converter with your engine/truck combo. Spending some quality time with this software could save you thousands of dollars in selecting the wrong parts. I can not say enough about the utility of this software.


What TBI and Vortec intake manifolds are available for my truck?
There are 3 aftermarket TBI intake manifolds that are out on the market today. Holley makes one that has 2” bores but requires you to use an older style EGR. GM performance parts make one that also has 2” bores but is designed to be used with Vortec heads. They will not work with non-Vortec heads since the intake runners are much taller. The only real bolt-on without any modification is the Edelbrock Performer TBI intake. It is a direct replacement for the stock intake manifold with no modifications required. Its only downfall is that it uses the stock size inlet bores that don’t allow you to use a larger TBI unit as previously mentioned. Your local machine shop can make easy work of this and the intake can be bored to accept 2” TBI units. The last option is to use an intake design to work with a carb and use a TBI adapter plate (i.e. GM or Trans Dapt). Some people go this route and have a tremendous amount of success.

The only direct Vortec-compatible intake is the marine version that I mentioned earlier. It allows the use of standard aftermarket fuel injectors. There are also some other modifications that are required to use this intake. The conversion link is here: http://www.pacificp.com/forum/viewtopic.php?t=317. There is also a Vortec-compatible TPI base manifold available if you'd like to switch to TPI induction.


Are there any other intake systems I could use for my Vortec engine?
Definitely. Some people have moved over to the GM RamJet for Vortec engines. Edelbrock also makes a MPFI system for Vortec heads. More and more manufacturers are making Vortec- compatible intakes and fuel injection systems. A less expensive option may be a TPI conversion (http://www.fullsizechevy.com/forums/...=marine+vortec). Visit Summit Racing for an up-to-date listing of Vortec-compatible systems. Weiand, for instance, has their new Stealth Ram for Vortec heads and even the weiand supercharger units for Vortec heads. Any of the products would be used with TBI engines that use Vortec or Vortec-style performance heads as well.


What about Edelbrock’s MPFI conversion for TBI engines or engines with Vortec heads? Is it worth it and how much power does it provide?
Another common question. Here is a good article on this kit: http://www.off-roadweb.com/tech/0310or_edel/. Edelbrock did their own testing using their performance parts (cam, heads, exhaust, etc.) and came up with about 270 hp. I use it, but I’ve matched it with Trick Flow heads and a cam from Comp Cams roller with more duration and higher lift. Here are the pro's and con's on this kit.

Pros:
1. I called Edelbrock and the supplied injectors are rated at 20.5#/hr at 43 psi. With tuning and maximal FP (~65 psi), these injectors are good up to 360 hp. You can also swap the injectors for larger ones, so you'll never exceed the hp limit of the fuel injectors,
2. Least expensive manufactured MPFI system on the market that's brand new.
3. Single plane intake design that works well with high flow heads/camshaft upgrades. Although torque is lower than a dual plane setup at lower RPMs, torque output is still significantly more than stock.
4. There is an aftermarket adjustable FPR available for it. There are several manufacturers, including Holley, Jet, Automotive, etc. I purchased the Holley one (512-502) and switched the output connector with an AN-6 one (Barry Grant 140028). Easy peasy. There is a schrader valve for a fuel pressure gauge off the driver's side fuel rail. It can be swapped out to work with an inexpensive underhood Autometer fuel pressure gauge. In order to make this work, you'll need to exchange the position of the fuel rails (driver's side fuel rail to passenger's side and vice versa for passenger's side fuel rail) and rotate them 180 degrees (Edelbrock engraving towards manifold). The fuel lines hook-ups will still be at the back, but on the opposite side. You will also need to create an access hole in the throttle cable mounting bracket to easily adjust the AFPR with an allen key.

Cons:
1. Relatively expensive for the performance gain on stock setup
2. Some improvement in highway fuel economy, but not much.
3. You can achieve similar performance from a TBI/chip for less money BUT you'll need larger injectors to match your power output.
4. Need a custom chip if you use any camshaft or cylinder head other than Edelbrock. The Edelbrock tune is not optimal anyway, and probably explains the poor performance some people have experienced. Save some money by ordering the 3502 kit, which is the same system w/o the Edelbrock-supplied chip.
5. Not a true PFI setup, since the PCM fires the injectors using the TBI firing strategy (twice as often as PFI). For a true conversion, you can use the PCM from a 94-95 truck (7427) and convert it to PFI: http://www.fullsizechevy.com/forums/...i-tbi-pcm.html. A good discussion topic on this can be found here: http://www.fullsizechevy.com/forums/...ur-trucks.html

[Devs93]

So to answer the question - is it worth it? On a mostly stock engine with stock heads - no. Even on a performance motor, I'm not sure if the added expense justifies the minimal performance gains relative to a TBI setup. TBI is capable of supporting engines with 360+ hp with FP/tuning/injector upgrades. Some people, however, have reported rich idle that they cannot tune out due to the TBI injector firing strategy with high pressure stock injectors or with the 454 injectors. Converting to PFI mode and running MPFI would eliminate this problem and allow you remove the bottleneck of TBI in a performance application. Most people would consider other performance upgrades first before attempting this swap.


What is involved in a TPI swap for my TBI engine?
This was a popular swap about ten years ago. I still think that this swap is economical and it has an important application in trucks since it is designed to produce a broad flat torque curve. Read these articles for more specifics on the conversion: http://www.chevyhiperformance.com/te.../148_0207_tpi/ and http://www.chevyhiperformance.com/techarticles/90759/. There are also entire books dedicated to this swap, such as the Chevy TPI Fuel Injection Swapper's Guide available through Summit Racing or at your local performance parts store. There is more involved in this swap than a short paragraph will allow. Here is a well put-together article detailing the swap on a 94 Suburban: http://www.edgesz28.com/edgesZ28/sub...an-tpiswap.htm. If you’re thinking about a TPI setup, I would try to choose your components to maximize torque/power under 4500 RPM. There are ways to improve top-end breathing on TPI engines, but the parts are expensive and not readily available. Adding these components can produce a 400hp TPI engine, but the added expense of the components will no longer make this an economical swap. If you want a 400 hp small block or high RPM performer, I’d consider using the GM Ramjet or Holley Stealth Ram instead. It will be cheaper to buy these systems than modify the TPI system for high RPM power.


What cylinder heads can I use on my truck?
There are a few choices that you can go with. A popular set of heads are those found on TPI Camaros/Firebirds/Corvettes, called the L98 head. They do not have the swirl port style of the stock TBI heads, but have the same combustion chamber size as your stock heads. They can be found in cast iron and aluminum, the aluminum being the most desirable because of their smaller 58cc combustion chamber. IMO though, there are better aftermarket heads available for TBI replacements. Another cast iron set is the World Products SR Torquer heads. These heads have larger than stock valves, the same combustion chamber as stock, and provisions to accept cams up to .525” lift. Other choices include AFR, Edelbrock, Trick Flow, Pro Topline, and Canfield. Personally, I love the Trick Flow heads for a few reasons: 62cc combustion chamber, direct bolt-on design, excellent flow characteristics, aluminum design, and relatively inexpensive. They come with several spring options to support 0.500” lift hydraulic and hydraulic roller camshafts.

Vortec heads are a good head from the factory, but also have their limitations (see “What are the major troublesome areas to overcome in TBI engines to make awesome power? In Vortec engines?”). At minimum, I would upgrade the springs on these heads to support high lift roller camshafts. If you are looking for more power, you will need to upgrade or replace your fuel induction system and should consider aftermarket Vortec heads. There are many heads available and here is a recent article on some of the more common choices: http://www.chevyhiperformance.com/te...tec/index.html. To save you the extra reading, the Edelbrock 170 Etecs are the best performing head on the market right now with valve lifts up to 0.575”. Awesome head. These heads are used on Edelbrock’s EFI 440hp 350 crate engine, which would make an outstanding turn-key drop in motor for any 88-98 OBS truck.


I want to use Vortec heads on my TBI engine. What is involved with the swap and what kind of power increase can I expect?
Oh man, if I got a dollar for every time this question is asked…OK, this swap is not as easy as swapping heads as you’ve probably figured out. There are a lot of hidden costs involved that add up very quickly. You need: 1. Vortec-compatible TBI manifold – currently only GM Performance Parts sells this and it is pricey. 2. driver’s side manifold needs to changed to utilize EGR. Can be pulled from a parts yards or buy headers for 96-99 5.7L trucks. 3. EGR tube - again get from a wrecking yard. 4. Vortec heads have low lift potential and will require either machine work or different springs for high lift cams. If you're changing heads, you might as well change the cam at the same time. Summit racing and others sell Vortecs heads with these modifications already performed. 5. You will need a custom chip regardless of what you do in order to maximize the potential of your engine. 6. You may need to upgrade your fuel pump, run an adjustable fuel pressure regulator, or run larger injectors to make sure you have enough fuel to support a substantial increase in horsepower over stock. Just adding Vortec heads may add only 20 hp because the TBI camshaft is so weak. To take advantage of these better flowing heads, you need to change the camshaft in your engine. All told, it is going to cost more than $850-1000+, not including the cost of the heads to make it run right and to avoid disappointment. With careful parts selection, you can achieve 320+ hp easy with a performance exhaust setup.


I want to use a 4 barrel 900 CFM Holley TBI. Can this be done?
Sure! Some methods are easier then others though... You won’t need it until your pushing over 400 HP or 6000 RPM on an extensively modified engine. At power levels below this, an upgraded 2-barrel TB can meet the required demands. You can either run an external injector driver and learn prom burning or go promless and do your own source coding to control it, or you can use an aftermarket ECU. Your choice.


Fuel injection is not for me. How do I swap my TBI (or Vortec CSFI) for a carburetor?
I know – I get it. You have a ton of experience with non-computer controlled vehicles and when properly tuned, they can perform just as well as EFI, right? Plus, there is no dreaded computer to deal with and the thought of controlling your air:fuel ratio using metering rods and jets gets your heart pounding. While of course it is possible to run a carb on these engines, there are some things to think about before plunging into this swap. If you have the 4L60E transmission on 93 and later trucks, you will need to use an aftermarket controller kit with a specialized throttle position sensor designed for carburetor “retrofit” applications. As for the engine, the key to a successful swap is to remove control of the computer to engine parts. Therefore, you need to replace the EFI system with a carb/intake combo and replace your computer-controlled distributor with a non-computer controlled distributor, ignition module, and coil. You will also need to modify the fuel system by installing an in-tank fuel pump or installing a 3-port, return style AFPR inline before the carb to lower the fuel pressure to a carb-friendly 5-8 psi. There are also some minor modifications that need to be made, such as throttle linkage, vacuum lines, etc., but essentially you’re done. Ok, you’re still convinced on performing the swap. Instructions are here: http://www.thirdgen.org/carbswap. An article on the different types of carbs available is here: http://www.thirdgen.org/pickacarb.


Can Seafoam improve the performance of my engine?
Maybe. The reason to use Seafoam (or GM top engine cleaner) is to remove the carbon deposits from your combustion chambers. Why? Two reasons: 1) To promote cleaner combustion, and 2) Because these deposits can increase the compression of your engine by taking up free air space. You won't notice using the stock chip, but if you use a performance chip with aggressive timing, it may cause the engine to ping when under load (WOT) and using 87 octane fuel. On TBI and Vortec engines, there is a knock sensor that decreases the timing if engine knock is detected. Using Seafoam in this case, may remove engine deposits and lower engine compression back to the stock configuration, eliminating the engine knock. The result: you regain the lost power and performance of your engine.


What is a good exhaust system for my truck and will too big of a system take away low end power?
A 3” exhaust will not decrease low end power at all. A dual 2.5” exhaust system is optimum. Also, you’ll want to decrease back pressure as much as possible and many people get this confused with scavenging. A full exhaust from headers, dual or single high flow cat(s), and cat-back really provides a major power boost. The stock exhaust is horrendously restrictive. Buy a pre-fabricated exhaust kit or have an exhaust shop make your exhaust from scratch. It is not much more money believe it or not. A little reading in this exhaust section should help you make an informed decision

[Devs93]

Are there any aftermarket y-pipes available that are mandrel bent?
Yes, Edelbrock makes them and they are 2 1/2” down pipes into a 3” intermediate pipe. It is sold as an off-road unit, but it would be emissions-compatible with the addition of an O2 sensor bung and a 3” catalytic converter. It is pricey at $160. Another option is using Magnaflow’s y-pipe for 94-95 trucks, 2 1/4” mandrel bent tubing and includes their high flow catalytic converter for $150 – a great deal. Although it is listed for direct-fit applications for 2WD 94-95 trucks, it can be used in 88-95 trucks by cutting the 3” end off and welding on an intermediate pipe to connect it to your muffler. JBA also makes a larger mandrel-bent y-pipe for 4WD models.

Another option for a true dual exhaust setup that is mandrel bent is to use Magnaflow's catalytic converter/head pipe replacement unit from the 96-99 5.7L. It has 2 1/2" pipe and two high-flow cats. Cut the ends off and run 2 1/2" pipes to dual mufflers and you've got yourself a true dual exhaust setup. Cost on the Magnaflow unit is $316.


Do exhaust upgrades make a difference?
You bet they do! Brian at TBIchips did some dyno testing before and after exhaust modifications with his "Black Magic" and "Blue Whale" projects. The conclusion is the factory setup is very restrictive: http://www.tbichips.com/blackmagic.htm. He pulled another 40 rwhp and 50 rwft-lbs by changing to a 2-1/2" y-pipe. From the text, it sounds like he was using shorty headers and a 3" Magnaflow cat in both dyno runs. The results are mainly from the y-pipe change, although I'm sure some revised PROM tuning contributed as well. Installing headers and a catback exhaust is not enough. You need to change everything!!


Do I need a catalytic converter? Will removing it make more power?
This is somewhat of a loaded question. We all know that catalytic converters are designed to reduce noxious gases that harm our ozone and contribute to global warming. Their fault lies in the fact that they can restrict exhaust airflow and therefore can limit hp. Some people remove their catalytic converter in the quest for more power. Is this the right thing to do? Well let me provide some objective evidence and you can make the decision yourself. A recent article in Sport Truck magazine tested the airflow characteristics of their high flow catalytic converters against stock GM, Ford, and Dodge units. Here’s where auto math becomes important. As mentioned earlier, most people over estimate the CFM requirements of their engine. CFM requirements are based on 3 factors: max engine RPM, intake manifold design, and volumetric efficiency (VE) of their engine. VE? What the heck is VE? Probably the most important factor influencing CFM engine requirements. To estimate your CFM requirements, go to this link: http://www.wallaceracing.com/intakecfm.php. Don’t all assume you have a performance engine. If you haven’t changed heads or cam on your TBI engine, VE at 4500-4700 RPM is only 67%. On a 350 TBI engine, CFM requirement is 383-473 CFM. Shocking I know!! If you have a hydraulic roller camshafts, performance heads and other performance goodies, you can choose a VE between 90-100%, but I bet there is <5% of the TBI crowd out there with that engine combination.

Back to the Sport Truck article, their 3” cat is rated at 360 cfm at 1.5inHg (quoted 422 cfm at 28” H2O) and their 2.5” cat is rated at 307 cfm at 1.5inHg (quoted 360 cfm at 28” H2O). This was surprising and I now know why catalytic converter manufacturers don’t cite their airflow characteristics. No one would buy them!! This is just a misinterpretation of the kind of airflow needed for an exhaust system. Let’s take our TBI engine above with performance exhaust – needing 383-473 CFM of air. Will a single 3” cat suffice? – Sure. Will it affect hp – a little bit, but limits it only by 2-4% or about 4-8 hp. Most people wouldn’t even be able to tell the difference. Let’s say now you’ve got an all out performance 350 with the works, hydraulic roller cam, long tubes, the best performance heads money can buy (95% VE – it is rarely 100% at max RPM!!), shifting at 5700 RPM (computer-limited). You’ll need a lot of air - 658 to 823 cfm and dual 3” catalytic converters (2 x 360 CFM = 720 CFM). Most engines are not that potent though. My engine, for example, with Trick Flow heads, Comp hydraulic camshaft, shifting at 5500 RPM has a VE of 83%. My engine needs 555 to 693 cfm. Dual 2.5” cats are more than enough not to limit hp. However, TBI engines only come with a single 3” cat and it is certainly not high flow. Removing the cat on a 2-into-1 exhaust system will improve power on a heavily modified engine – there’s no question. So depending on how you feel about saving our environment versus the additional expense of 2 catalytic converters and a custom exhaust, only you can make that decision. All I can say is TBI engines with stock heads and cam do not need to remove the stock catalytic converter, unless it is plugged or faulty (or the ancient pellet-type). There is no significant change in power with or without a high-flow catalytic converter. Vortec 350 engines already come with 2 catalytic converters from the factory that is more than enough to meet your performance upgrade potential.


What is a smog pump (on pre-93 trucks) and can I remove it?
Your smog pump (AIR pump) is simply what it sounds like. It is a pump that sends air to your catalytic converter via a little round tube. This helps complete the combustion of residual exhaust gases in your catalytic converter along with quickly heating up your cat during cold starts. Replace the catalytic converter with a modern unit and the AIR system becomes redundant. It is located on the lower side of your accessory bracket right underneath the AC compressor on the passenger side. It has an upper and lower bolt that attaches it to the bracket. These bolts can be removed and your smog pump will come right out. Here is an article on smog pump removal: http://www.thirdgen.org/serpentine


I have a lot of performance components already on my 305 engine, but I want more power. What should I do?
Well, any performance upgrade that you can do on a 350 engine can also be done on a 305 engine. If you want more than that, then add a supercharger or buy a 350 long block or 383 short block with aftermarket heads and swap over the parts you want. 350 engines are so plentiful that IMO, there is no excuse for not having one for the serious performance-minded individual.

[Devs93]

I like the 454SS, but I have a small block in my truck. Would you recommend a 454 engine swap in place of my engine?
Well, any engine swap is possible. There is no doubt the 454 engine is super cool and you can swap it into your truck, but because of the extra torque, you’ll need to upgrade the transmission, preferably to the 4L80E or Turbo 400. The upgraded 4L65E found in performance trucks/cars may also be used, but right now they are relatively new and difficult to find in the wrecking yard. A new transmission would be pretty expensive, but like I said, anything is possible. Another option is to buy a World Products assembled small block short block. They make these up to 454 cid (http://www.worldcastings.com/prods_pages/101202.htm). I think the “most wanted” of all the big block swaps is the 572 GM Performance Parts engine. Man, that engine would be so cool in an OBS truck. If you can afford that engine, then you can afford the swap.

Personally, I think doing a LS1 swap is very affordable right now. There are enough donor vehicles in the wrecking yard from crashed Vettes, Camaros, and Firebirds to make this an awesome engine swap project. Jimmy P is currently installing one on his 1989 Silverado project: http://www.fullsizechevy.com/forums/...d.php?t=144018. Another modern engine swap would be to use the 5.3L out of the NBS trucks.


Are there any nitrous systems designed for my TBI or Vortec truck?
Yup. Nitrous Works, Nitrous Oxide Systems (NOS), and Venom Performance all make nitrous oxide systems for 88-95 TBI-powered trucks. For Vortec-powered 96-98 trucks, NOS and Venom have systems available. Visit their respective websites for more information and where to buy. You can add up to 125 hp with these kits. Nitrous kits on trucks get a bad rap from the ricer market, but they can safely add power for not too much money. Kits are priced between $600-800 and can be easily installed yourself. It provides the same power as a supercharger, but at a fraction of the cost. When used properly, a good nitrous system is a welcome addition to any truck engine. The problem is you can only use it at WOT and you have to keep refilling the nitrous bottles.


Where can I find TBI-engine related performance parts for my truck?

Performance Chips:
Wester’s Garage - http://westers_garage.eidnet.org/Index2.htm
Wait4Me - http://www.wait4meperformance.com/
TBI Chips - http://www.tbichips.com/

Larger Throttle bodies:
CFMTech - http://www.cfm-tech.com/index.htm
XtremeFI - http://www.xtremefi.com/
TurboCity – http://www.turbocity.com/default.php?cPath=16

TBI injectors:
TurboCity – http://www.turbocity.com/default.php?cPath=16


What are performance chips or performance tunes and how do they work?
Performance chips are essentially a memory chip that contains a set of instructions that tells your computer (and your truck engine) how to respond to incoming sensor data. Performance tunes differ in that the set of instructions are contained on flashable memory housed inside the computer. Therefore, there is no chip to replace. Chips are available for both the TBI and Vortec Engines. Jet Performance, for instance, makes performance chips for Vortec engines. Other performance chipmakers are out there as well, including Wester’s Garage, Wait4Me, TBI Chips, (Ed Wright) Fast Chips, etc. They can vary in price from under $100 to over $500. Burning your own chips can save you some money or at least allow you to fine tune your engine as you continue to upgrade your engine.



What is chip burning and is it necessary?
Chip burning is simply making your own custom PROMS. You will find that the biggest gains on these engines will come from burning your own chips. The stock chip is very weak and can barely support the factory set-up. Anytime you mod your truck you should look into burning a new chip to maximize its potential. You can get away with the stock chip with basic bolt-ons, but once you add a major upgrade (i.e. new camshaft) chip burning is a must. Alternatively, you can have a performance tuner make one for you, but it will be difficult to get your engine dialed in properly since the chip is made using info on your engine combination, but it is not YOUR engine without any feedback to see how well the tune is working. The solution: datalogging. There is free software available that you can install on a laptop computer and use a special connector to plug the laptop into your cars diagnostic (ALDL) port. Driving the truck while this software is running will collect performance-related data about your engine. These data will tell you what your engine is doing with respect to timing, air:fuel ratio, etc. at respective engine RPM. You can save this data and send it to a chipmaker that will burn you a chip based on the info you sent them. Retest with the datalogging software and finetune the chip again. This strategy will essentially accomplish the same thing as if you were burning the chip yourself. You can find this program from the following link.
Link to data log software
Link: Good starting post for TBI prom tuning


Is my TBI or Vortec speed limited?
Yes, the ECMs have a fuel shut-off circuit once the vehicle reaches the maximum limited speed. Any chipmaker or aftermarket chip/tuner will remove the governor circuit to allow higher speeds. There is no RPM limiter, but max RPM on Vortec engines seems to be 5800 RPM. This is written into the computer code. Some people are trying to develop ways to get around this.


How can I learn how to burn my own chips for my TBI or Vortec engine?
Lots of good resources here/lots to read and way too much to cover:
http://www.fullsizechevy.com/forums/...ad.php?t=45225
http://www.thirdgen.org/techboard/tb...free-tune.html
http://www.thirdgen.org/techboard/di...uide-book.html
http://www.fullsizechevy.com/forums/...d.php?t=126937
http://www.fullsizechevy.com/forums/...d.php?t=139132


What is a torque converter and how does it work?
The torque converter is an amazing piece of automotive engineering that connects the output of the engine to the input shaft of the transmission. It is a fluid-coupling device that also acts as a torque multiplier during initial acceleration. Torque converters are rated in terms of stall speed. Stall speed refers the RPM that a given torque converter (impeller) has to spin in order for it to overcome a given amount of load and begin moving the turbine. In other words, it refers to how fast (RPM) the torque converter must spin to generate enough fluid force on the turbine to overcome the resting inertia of the vehicle at wide open throttle. Most torque converter are rated using a reference load of 230 ft-lbs at 2500 RPM. Engines producing more than 230 ft-lbs at 2500 RPM will give you more than advertised stall speed. The opposite is true for engine with less than 230 ft-lbs at 2500 RPM. The increase or decrease in advertised stall speed is only 100-200 RPMs.


How do I choose the right converter for my application?
Choosing the right torque converter is similar to choosing the right camshaft. It can be difficult and it is easy to get bogged down in technical information. The main factor is related to your camshaft choice, since this affects the powerband of the engine. A good rule of thumb is for advertised cam durations up to 260 degrees, a 2000 or 2400 stall converter is a good choice. Advertised cam durations up to 272 degrees, a 2400 or 3000 stall converter is a good choice. Advertised cam durations over 280 degrees, a 3000 to 3600 stall converter is a must.


What are the drivability concerns of a higher stall torque converter?
Proper torque converter selection is the key. You will not have any drivability problems if the torque converter is matched properly to your application. Mismatched components are where problems come in. For instance, if you have an engine that needs a 3000 RPM stall and you install a 2200 (2000 to 2500 RPM) stall converter, it will normally not even provide a 2000 RPM stall, but act very similar to the stock converter you just replaced. How come? Because the engine needs to operate in its optimum RPM range and since the stock torque converter is below that range, it is not getting enough load from the crankshaft side to operate as designed. In other words, the low-RPM torque is much lower on this engine and therefore reduces the advertised stall speed of the converter to under 2000 RPM, similar to the stock unit (around 1600-1800 RPM). Symptoms include engine stalling when in gear while stopped, low stall speed, hesitation when at going to WOT, and bogging of the engine when leaving from stop under WOT. Likewise, too high a stall speed is not good either. Symptoms include high “revs” to pull away from a stop, “marshmallow” accelerator feel when driving at part throttle, transmission and possibly engine overheating, and a pronounced engine rev when nailing the throttle from a cruising speed.


How do I determine the stall speed of my torque converter?
You should be able to footbrake stall the converter to its rated stall speed. If your torque converter has a 2400RPM stall speed, you should be able to footbrake stall the converter to about 2400 RPM.


So when should I upgrade my torque converter?
IMO, not until you’ve upgraded your camshaft. A 2500 RPM stall torque converter installed on a stock TBI engine is a major mismatch. A 3000 RPM stall converter on a stock TBI engine is just plain ridiculous, and you’ve just lost the majority of your engine’s powerband.

[Devs93]

What are some ways to improve automatic transmission performance?
There are two commonly found 4-speed automatic transmissions: 4L60/700R4 or 4L60E. GM rated these transmissions up to 370 lbs-ft of torque. The heavy-duty 4L80E had a much higher torque capacity rating and was used in 1991 and later GM vehicles, but its use was limited to 454SS OBS trucks only. If you want to really improve the torque capacity of your transmission, you need to rebuild it using a performance rebuild kit that include performance bands and clutch packs from companies like TCI automotive (Pro Super kit) and Jet Performance. This will improve your transmission’s torque capacity up to 470-500 lbs/ft or enough to support over 450 hp. Some high performance heavy duty kits will even support up to 650 hp. Whole transmissions can be also be purchased. Monster Transmission and Performance (http://www.eatmyshift.com/) has 2 levels of upgraded 700R4 and 4L60E transmissions available starting at $1895, no core charge, and free shipping.

There are also simple ways to improve your transmission’s shifting performance and increase the life of the transmission bands by installing a transmission shift kit and installing larger servos from Sonnax (or Jet Performance). A popular upgrade is to install the Corvette (or even larger billet) servo that activates the 2-4 band assembly to guard against slippage while in 2nd gear. It will also help to quicken the 1-2 shift. There is also a 4th gear servo that can be installed that helps to firm up the 3-4 shift and hold the shift band tighter to prevent wear. A shift kit will provide stronger, quicker shifts through out the transmission bands. Either of these upgrades can be perform alone or in conjunction with one another. However, these upgrades will not improve the torque capacity of the transmission, but they will help to reduce wear (slippage) of the transmission bands and may prolong the life of your transmission.

If you have a 4L60E transmission, B&M also makes a product called the Shift Improver Plus+ that splices onto two wires leading from your ECM to the transmission. It has a rocker switch that has two settings on it: firm and extra firm. It serves to electronically increase the line pressure to hold the transmission bands and quicken shifts (similar in function to the TV cable on 700R4 transmissions). I’ve used one on my truck and it does work. This would be a good option for those that occasionally tow or want performance shifts, but not all the time.


What about rear end upgrades? Any good?
We’re talking rear end gears here. This discussion goes hand-in-hand with tire size, because with many truck owners are installing larger 20” or 22” wheels, and it is not unheard of now to have tires that are between 29-32” and much taller than the factory-supplied tires. Take my factory tire for example. It was a 235/75R15 or a 29” tall tire. I’m running a 265/50R20 tire or a 30.5” tall tire and my truck has a 3.42:1 rear end. The addition of these tires to my truck would be equivalent to a similar truck with the stock 29” tires and a 3.25:1 ratio rear end. In order to restore the performance that I had with the stock tires, I would theoretically need a 3.60:1 rear end. Since one isn’t made, the closest one would be a 3.73:1. For 33” tires, I’d theoretically need a 3.90:1 rear end. A good rear end ratio calculator can be found here: http://www.idavette.net/tech/ratioc.htm.


What about rear end differentials? What kinds are there? Do I need one?
Most trucks these days come with mechanically locking differentials, although there are both 2WD and 4WD trucks that have open differentials. Find the RPO codes on your truck (usually in the glovebox) and then check here: http://www.fullsizechevy.com/forums/...d.php?t=164851. The mechanically locking differential is a speed sensitive design that reacts to wheel slip by sensing when one wheel is spinning substantially faster than the other. So most of the time it works as a regular open differential, but as soon as wheel slip happens, going forward or reverse, the locker immediately kicks in. Note axle lockup can only occur at speeds below 20 mph. A simple design and it works well. For some reason, it gets knocked down in favor of the limited-slip differential. GM uses the Eaton G80 mechanical locking differential: http://www.traction.eaton.com/prod2.htm. A better design is available with the Eaton E-locker, which is essentially a mechanical locking differential where the driver has complete control of when and what gets locked.

Another design is the limited-slip differential (http://www.traction.eaton.com/prod3.htm). It uses input torque rather then wheel slip to activate the locker. A common misconception is a limited slip differential provides traction to both wheels all the time. With normal or light throttle applications on dry pavement, only the drive wheel receives torque (or power) - just like an open differential. Detroit Locker makes a clutchless design with no clutch packs to wear out called the Detroit TruTrac (http://www.detroitlocker.com/DT.htm). A great design and should be standard for all limited-slip differentials.

Another new product is the Detroit Electrac (http://www.detroitlocker.com/DE.htm), combining the utility of the TruTrac limited-slip differential with electronic user activation of a full locker controlled by a switch mounted on the dash. The ultimate combination and the best of both worlds.

[Devs93]

Do you need one and which one? Well, in most cases, no. But there are times where a limited-slip or mechanical locking differential is extremely useful, especially in a truck. Winter traction is a good example, particularly with 2WD trucks. While the limited-slip differential is an excellent way to control traction in street rods, light duty/street performance pickups and all types of tarmac running racecars, it isn't the best solution for the serious off-road vehicle. Why? Because it's input torque, not wheel slip that determines when power is transferred to the other wheel. So for winter roads, the boat ramp, and the back-woods, two-track, gotta-get-over-the-mountain types, choose the mechanical locking differential. IMO, either of these two is better than the open differential design.


Will an MSD or equivalent ignition box improve the power and performance of my truck?
IMO, a MSD ignition box will not outperform a well-tuned and maintained stock HEI setup. I think they have their applications with superchargers and nitrous systems, but not on a mildly modded 350 engine. And it’s debatable whether or not it improves fuel economy with more complete combustion. Does it start faster or easier in winter? I don’t believe so – that’s a myth. Quicker throttle response? Again – a well-tuned HEI distributor works just as well – no difference in throttle response. So why use one? I can think of a couple reasons: 1) RPM limiter capability, 2) some have the capability to adjust your timing/retard without having to play with the distributor, 3) may make up for a poor tuned HEI system, bad/faulty wires, etc. – not a great reason, but it will make your ignition user friendly and resistant to the common faults of poor maintenance, 4) more consistent ignition and higher speak energy when above 6000 RPM. IMO save your money for performance upgrades that are proven to make more power. The stock ignition can easily support 400-450 hp and operate flawlessly to 6000 RPM.


What about power or underdrive pulleys? Do they make more power and how do they work?
I have March Power Pulleys – IMO you won't notice any difference in power. They are designed to slow the fan speed at higher engine RPMs, so that's where your benefit will be. Unfortunately, TBI's only rev to about 4500-4700 RPM, so I don't feel they are worth it, particularly if you have a clutch fan setup. With the clutch fan engaged, they probably improve power (see next question), but I wouldn't buy them again and get electric fans instead. They can also reduce the amperage of your alternator at idle despite the smaller alternator pulley. This is particularly important at night with your lights/fog lights on, stereo pumping, A/C or heater on full blast, and you’re at the stop light with your brakes on. Oh yeah, you know what I’m talking about.


What about electric fans? Do they make more power and how do they work?
I wouldn’t expect performance miracles from an electric fan. They do improve power, but not in the way that you’d think. I’d called them more of a power retainer than a power adder. Here’s how they work. Installing an electric fan on your engine removes the parasitic action of the motor turning the fan to facilitate air flow across the radiator. Normally, a clutch fan helps to reduce to the fan speed when the engine does not need maximum cooling from your engine-driven fan. Removing this fan improves power, but like a 2-3% hp improvement versus a clutch fan. OK so how can these electric fan manufacturers claim a 20+hp improvement? Well it does happen, but on a HOT engine with the clutch ENGAGED. Yup, that’s right – they are also including the hp that you would normally lose due to the engaged fan. So e-fans really do work.



What about suspension upgrades? How can I make my truck handle better?
The easiest way is to replace your rubber suspension mount bushings with polyurethane bushings. At a minimum, you should replace your front sway bar mounts and sway bar end links. Make sure you use lots of grease before installing them or they will squeak. Energy suspension also sells sway bar mounts with greasable zerks. Next upgrade would be to add a rear sway bar available from companies like Hotchkis, Belltech, or Hellwig. I installed the Hellwig rear sway bar on my truck. It works well and improved the cornering capability considerably. I would recommend getting the axle mounts tack welded in place (any muffler shop will do it), because they will not hold with the U-clamp design. Another option is using sway control bars from Summit or other auto parts stores (http://www.autopn.com/autoparts/swaycontrol/index.html). They are cheaper than adding a rear sway bar. Of course, you can also install a drop kit, particularly one with drop springs and drop shocks. Lower center of gravity and stiffer springs and shocks will definitely improve your handling, but your ride quality may suffer. Too harsh of ride? Use spindles or drop LCAs instead and you can retain your stock front springs. There are also rear shock extenders that will allow you to use your stock length shocks. Another option is bagging your truck for better handling and ride quality.


OK, I’ve got ALL the right performance parts, heads, cam, tranny upgrades. Is there something I’m missing?
Could be. I’d say the most commonly overlooked areas that have a huge impact on performance is fuel supply and computer tuning. “Yeah, but I’ve got a performance chip, an AFPR, and larger injectors so I’m covered.” You may think so, but in most cases your truck is not meeting its potential. How many of you guys datalog to make sure your performance components are working at their maximum potential? How many of you guys install a fuel pressure gauge when you install your AFPR? You’re not alone – in fact, a majority of people don’t and yet it is the easiest way to both improve your engine’s power and fuel economy!! What’s that, you say, better fuel economy? Oh yeah, baby!!

Most people do not understand how much fuel they really need. With ANY performance upgrade, you may need to make changes in the amount of fuel delivered and WHEN it is delivered for your truck to run tip-top. Many will buy an AFPR and play with the pressure settings, but they fail to purchase a fuel gauge!! Please read my tutorial of properly matching fuel to your performance upgrades: http://www.fullsizechevy.com/forums/...d.php?t=200226. In order to refine the fuel deliver for the best power and fuel economy, you have to be able to adjust the computer settings. This is why doing your own chip burning is so important. Please refer to the chip burning section in this thread for ways to either do it yourself or empower yourself with “datalogging” so that a chip/tune specialist can properly make a chip/tune for your engine.

Another method for fine tuning your engine is to adjust your fuel mixture via the O2 sensor and a digital volt meter. Keep in mind that the ECM controls fuel tables as well, so if you’ve changed heads/cam or injectors, but haven’t changed your chip to recalibrate your fuel tables– this is not going to work. However, if you’ve done mild mods or re-calibrated your ECM for your engine mods, this is a good way to fine tune the air:fuel mixture for optimal performance. The article is here: http://www.thirdgen.org/o2tuning.

If you’ve spent major dollars on performance upgrades, you owe it to yourself to properly tune the combination that you have. Guaranteed this is the single best way to make power. Assuming you have the right parts is like throwing money (and hp) away and defeats the purpose of why you are upgrading your engine in the first place.