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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
When the throttle plate is slammed closed the CBV opens to keep the turbo from being damaged and to help keep it from stalling. When this valve opens it relieves air from the between the turbo in the intake valves.

Where it bleeds it to is back to the pipe that comes from the metering area and before the turbo suction side.

If any excess air is bled our of the system after it goes through the metering plate the motor will get to much fuel!

There is another valve on the C2T and other turbos that allows some air to escape around the throttle plate when the car decelerates. The is partially for emissions but also helps keep the turbo from stalling.

Work I and another did on our turbos resulted in the head that IA is using for more fuel. He took our head builder and ran with it. I did not pursue that strategy because there are some problems with how it changes the rate of fuel delivery. Basically that mod delivers more fuel every where along the curve. You can get it set right at idle and it will be to rich at cruse. Get it right at curse and it will be lean at idle. Yes, it dose deliver more fuel. At first we disconnected the boost circuit on the WUR because it ran to rich on boost to. It was my idea to add an rpm switch to limit the boost enrichment cycle. All that dose is add to the lag issue.

I had a programmable system that would have allowed me to tune around these issues. Now with the programmable WUR these issues should be controllable. The new programmable WUR uses a stepper motor. My system bled off pressure around the stock WUR of which I disabled the boost enrichment cycle. I no longer needed this because I had total control over my Control Pressure.

Again, half the secrets to taking the lag our of a CIS turbo is in reducing the back pressure after the turbo and getting the metering plate out of the way.


My changes in how the CBV worked was icing on the cake.
Old 12-05-2008, 04:20 PM
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