Cjshutts

I used to belong to a Grand National club, and they used to turn up the fuel pressure to 60-75 psi, then if needed, they would install larger injectors. Some of the cars had chips, but for an additional 100 hp I think you could crank up the fuel pressure and maybe go with bigger injectors.

Also, are you going to to go rotory (roots style) of centrifugal?

Just curious, this months Hot Rod has some new supercharger kits in it from Paxton.

PaulW

1. Use a rising rate fuel pressure regulator and stock ECU. The ECU doesn't know that the car is being boosted, but if you get a rising rate fuel pressure regulator, it adds more fuel with the boost....during normal vacuum operations, it doesn't add any fuel.

The ECU changes things based on O2 sensors and knock sensors still. You adjust the regulator so that it sees a proper mixture by monitoring with vag-com.

<img src="http://www.cartech.net/images/fmu2020.jpg">

Have not done fuel flow tests, but it appears that new injectors will be required....but this can pass more fuel through the injector.

2. Basically do the same as above, but reprogram the ECU.....since I really don't know anything about reflashing a chip....I have two books on order, so maybe I can learn.

I have a chip now socketed on my ECU.....so I guess I could reflash a new chip and install it or just work with somebody like PowerChips to do it for me.

And I will use a centifugal blower, won't change low end power really at all, but will drastically change high end power, Rotex has a really neat unit that has a thermal efficiency of 76%, a roots blower is closer to 55%, so it adds a lot of heat.

pw

Cjshutts

varied by the injector pulse width duration, so I would think that with higher fuel pressure under low boost conditions, the ECU would automatically adjust based on the O2 sensor feedback and keep the injector open for a shorter amount of time. If this is true, you may just need to get an fixed, adjustable fuel pressure regulator.

PaulW

1. The stock ECU map has a pulse duration for a given throttle position, engine RPM, etc. It fine tunes with the 02 sensor. The car would run severly lean with no changes in fuel pressure with boost or ECU mapping changes.....this would mean big trouble and things would overheat and blow up! Or if you put more fuel in because of a higher pressuure fuel regulator, it would run way too rich less than 3K RPM, where you run the car 95% of the time.

2. You really can't exceed an 85% duty cycle on an injector.....it can only flow so much fuel. To get an extra 100 HP on a 300 HP machine, you need an extra 33% fuel. Very doubtful that our stock injectors would flow that, even under higher fuel pressure. And looking at the few kits that exist for Audis, they all include new injectors. Fuel flow calculations and testing are in my near future. I will be able to make conclusions at that time.

3. The rising rate fuel pressure regulator does not change the fuel pressure until you have boost. It actually piggy backs on the stock fuel pressure regulator which maintains a given pressure above manifold pressure (which changes with engine load). Once there is boost, it adds fuel (by raising fuel rail pressure) to maintain the problem fuel/air mixture using the given ECU map injector duty cycle.

Once boosted, you'd like to maintain about a 13:1 air fuel ratio to get power, cool the chamber and stay away from detonation which is the death of all supercharged engines.

And what I have written is just my recent knowledge, so it might not be 100% correct (well, I'm sure of that), but it's general practice.

pw

GDJT Allroad^2

You got it!

mclarenm8d

... but I believe the S4 guys are using Split Second controllers and the asundery other competitors in that category. Split Second has a pretty cool product PDF on their website. Opinions vary on who is the best for a given product type and application.

As far as an application on a VAG 4.2 ??? One might have to follow along the path of work done on a Motronic MB or BMW V8.

I'm convinced that a 4.2 can "burn through" fuel delivery through aggressive Lemmiwinks tweaks of spark advance at relatively low RPM's (~3200), no matter what fuel correction factors are applied. One can get a 4.2 to pull like a turbodiesel down low but then it will ping like a rattlesnake as it crosses into program max advance. This is an issue more serious than simply pre-ignition, it burns through its fuel delivery.

Just reinforcing the importance of getting the fuel calculations correct :-).