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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
In case anyone wants to try is I set my Compressor Bypass Valve (what Porsche called it with the C2 Turbo) so it was open all the time with cruse and idle. This would keep the turbo spinning faster than with it closed and created a usable reserve. It was set so when I went from a manifold vac condition like at cruse and idle, it quickly closed. This gave me faster boost response.

Typically the CBV only opens upon closing the throttle at higher RPMs. This can not be done with the factory Bosch unit. To work it must have a larger surface area on the piston in the upper chamber (with the vac boost line attached) than the valve area. This way when the boost pressure builds in the upper chamber it can push the valve closed against the boost pressure off the inter-cooler.

I used one that looked like the Forge unit but it had adjustable spring tension in the upper chamber. I played with the spring tension using a hand operated vac pump to tune it.

It worked quite well for me years ago. I also had a frequency valve plumed around the WUR run by a controller that was was mappable as to rpm and manifold pressure. This allowed me to quickly reduce control pressure with acceleration to get the metering plate moving much faster. It also helped cure the lean surge typical with CIS and let me tune the air fuel ratio at all rpm points.

I had great throttle response between the two systems.
Old 02-26-2009, 06:46 PM
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