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Old 10-31-2012, 09:25 AM   #3
Devs93
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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.
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