[s-cars] Fuel Pressure Test Results

CaptMagu at aol.com CaptMagu at aol.com
Tue Jul 27 09:09:54 EDT 2004

Dave , Ned and all

I thought I would respond to Dave's off and online queries online for wider 
dissimenation and of course flaming. First off, thanks for your findings Ned. 
And thanks Dave for your energy in this matter. I know its probably fueled by 
your desire for an answer to your problem but you are definately a driven man!

Here in the rarified air of Evahboost and Denver, most of us don't have 
fuel/detonation issues. That changed for me when I ventured down to sea level with 
the Happersized wundercar last year for the ACNA Nationals. First of all, I 
couldn't run full boost on my old software because I was getting premature MAF 
cut because of the denser air. I had to pull the boost back to 22 lbs. Even so, 
when I had the car on the dyno to baseline my fuel pressure at sea level, I 
noticed a disturbing trend in the air/fuel ratio and fuel pressure. After 6000 
rpms the AFR would climb beyond 12.0 towards 13.0 and the fuel pressure would 
drop from 88 psi down to about 80psi(I did and do have a fuel pressure gauge 
under the hood). The dyno tech stated that many of the 1.8 liter Audis that he 
had dynoed required a replumbing of their fuel lines to get to horsepower 
levels beyond 350 hp. He said that my AFRs were very similar to the 1.8s and some 
of the other cars he dynos. His suggestion was to replumb with larger lines 
and get a high flow fuel pump. I never did get any detonation but I do closely 
monitor boost, AFR, and EGT.

To review, when I got back to Evahboost, I had several discussions with Dave 
Jones at ASW about how we might remedy this issue. His solution was to borrow 
what they had done with their European Car Challenge 1.8 and S4 cars. We 
incorporated a fuel reservoir under the hood that is fed by the stock pump, the 044 
Bosch Motorsport high flow pump, and larger fuel lines from the reservoir to 
the fuel rail. This approach does not require the very time consuming and 
therefore expensive replumbing of all the fuel lines from the tank forward. At the 
time of these mods I knew I was going with larger injectors, new 
software(custom dyno tuned), to eventually feed a new turbo(GT 35R) with tubular exhaust 

These are my findings and solutions, now let's look at Dave's issues. First 
of all, the stock fuel pump was never designed to handle RS2 power levels. That 
said, your pumps are probably well within their design criteria. I think that 
some of your recent voltage findings and thoughts might prove fruitful. I 
would try this first. If it doesn't work, I'd go with the 044 pump. I'd also get 
a wideband AFR gauge for monitoring and analysis.

Hap, talkin dahkine fuelflow in Evahboost, Maguire

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