LaserK04

97 1.8T with K04 (non-DBW, obviously)
GIAC with 310cc injectors and 3 bar regulator.

I don't have a wideband 02. I know it's really the only right way to do this, but....

This setup worked well with the stock intercooler. Was seeing approx 15-16 psi tapering to 10-11 up top. 02 voltage was in the 0.875 range, falling to 0.86 way up top (over 6500 revs). From what I understnad, a safe yet not overly rich mixture, based on that voltage.

I recently added a RaceTec FMIC. Instantly, I was making 18-20 psi falling to 13-14 at redline. MUCH more than pre-FMIC because of reduced pressure drop. Now, the non-DBW has no ability to measure boost pressure in the manifold, and to my knowledge boost regulation is done by caclulations off the MAF sensor. This poses a problem, because the car has no idea it's getting more "actual" boost as result of the reduced pressure drop, hence it runs leaner. This now has 02 voltage in the 0.83-0.82 range falling to near 0.80 up top. I assume this is way too lean, so I am going easy on the car.

A few questions for those of you who have experimented more than I have:

By increasing fuel pressure (perhaps by going back to the stock 4 bar regulator or tweaking an adjustable one) will this enrichen wide open throttle fueling across the board, or will it make the car overly rich at part throttle? I've heard rumors that over a certain boost level (12 psi IIRC), all the bosch regualtors, be it 3 bar or 5 bar, generate the same fuel pressure.

Do I need to swap injectors yet again to perhaps a 330cc? Is there a method to calculate how much larger an injector i should try?

What is the target 02 voltage I should shoot for on a car used for a lot of open track events and DE's?

Any and all help, or experiences are appreciated. If you need more info let me know.

DAP@EPL

The FMIC has INCREASED pressure drop over the stock IC. Because of this the car has to run higher boost to get the same airflow (MAF).

-Dave Pramanik

LaserK04

No. This is a MUCH freer flowing core than the stock IC.

Big Nodge

when i went from 3bar to 4bar with the 310cc injectors, the difference was as you guessed most notable at partial throttle based on the fuel trims in block 32. However, it did shift the WOT O2v curve from block 31 up a bit. So it definately had an effect on WOT fueling. But, it sounds like you need more of difference than the 4bar will provide. You could always try it out though, I'm sure you could handle the swap since you showed me how to do it

Oh, how do you think your chip would perform with an Evo FMIC, which will have a slight pressure drop, as opposed to the racetec?

Audi2ptzero

When you changed to a FMIC you pretty much changed the temps of the air charge and a colder air charge is going to have a much denser air. Now the maf is still getting the same reading and the motor is giving the same about of fuel, but since there is more air to burn your air/fuel ratio is changing and causing the car to run leaner. The only thing you can pretty much do for this is to maybe step up to a 3.5 bar fuel pressure or an adjustable one that will allow you to fine tune the car.

Audi2ptzero

while the hotter the air gets the higher the pressure becomes. But as we all know, colder air makes more power. If you use colder air to make more power, you end up increasing the air flow on the compressor side which sucks in more air past the maf. The down side is that when you lower the air temps the car starts to run leaner because the air to fuel ratio changes.

LaserK04

Tried the 4 bar, and 02 voltage is back up to the .86-.85 range. So far no ill effects and part throttle still feels fine.

Picked up an adjustable regulator as well, just need to get a better gauge to tune it in. My guess is my ideal pressure will be a hair over 4 bar. Time to get the wideband on it.....

FASTandSILVER

"The down side is that when you lower the air temps the car starts to run leaner because the air to fuel ratio changes."

The ECU compensates the Intake Temperature changes using the IAT sensor into intake manifold.

Audi2ptzero

Because even the 02 sensor stops being used at WOT, which makes me think that the IAT sensor also stops being used at WOT.

LaserK04

I see less boost on a really cold day, sometimes as much as 2-3 psi across the rev band. The argument can be made that the MAF reading denser air pulls the boost back, but my MAF maxxes out at 4800 rpm, so above that, it has to be getting feedback from somewhere, or it'd give me the same boost all the time.

Just my opinion.