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Have a question for any A1 guys out there, what do you run for fuel pressure? do you stick with factory specs or do you shim it to try and up the pressure a couple bars?
Is it worth looking into raising it or do you not gain anything by this?
TIA
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Boosting fuel pressure does not really do anything from what i can tell, lap times ect. we normally run at about 78 lbs, and that is stock, im pretty sure, we tried running it at 90 lbs, but to no advantage.
Derek
I suspect the question is really "will increasing fuel pressure richen the mixture?" And the answer in a Bosch CIS system is no. If the system is working properly.
The fuel flow rate is determined by the differential pressure valves in the fuel distributor, and these valves always provide a 1.5 psi drop across the inlet pipe to the fuel injectors (in the fuel distribution unit). The Bosch engineers did this on purpose to maintain a constant fuel delivery in the presence of fuel pressure fluctuations from the pump. Even the pressure accumulator cannot damp out all of the pressure spikes.
If you want to richen the mixture, you need to figure out a way to increase the "slit opening" in the fuel distributor for a given airflow. The way to do that is to increase the duty cycle on the full throttle enrichment (FTE) switch or by decreasing the control pressure to the fuel distributor. This is what I, and many others do, to richen the mixture.
On my GP car, I have a system that will adjust the control pressure and can vary it from 30psi to 50 psi at will. This allows me to adjust the EGT from <1200F to >1400F at the twist of a knob while I'm driving.
You can also modify your control pressure regulator by either shimming the warmup strip or by knocking its mounting stud further into the housing (.010"-.015" ought to richen it up enough for you).
If you'd like to learn more how to adjust the CIS and CIS-E systems, I can be reached at [email protected]. I've played with the fuel system a lot, and am learning more and more as I develop the CIS for my prod car.
Mark Coffin
#14 GP VW Scirocco
#44 ITC VW Rabbit
Thanks for the replies, I did buy the plans from you Mark on the adjustable control pressure, so I am installing that now.
I was just curious if there was anything to gain by upping the fuel pressure as a whole.
Still learning this CIS stuff as well, in that never ending search for a edge here or there.
As Dr. Mark said, you can "play" with the Control Pressure to richen the air/fuel mixture. On my CIS system, I leave the System Pressure close to the factory values, and vary the Control Pressure for the ratio of the fuel to air. Regards, Ryan.
Boosting the fuel pressure is only helpful for forced induction, and even then it must be in combination with control pressure mods (e.g., increased control pressure except under boost). A better idea for IT might actually be to reduce system fuel pressure in order to be able to run a lower control pressure for the same mixture strength, and thus reduce the downward force that the incoming air must overcome at the fuel distributor plate. Unfortunately, this leads to other problems...