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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
With a CIS car we do not want to vent any air from the area after the air metering assembly.

Any air vented between shifts needs to be looped around the turbo to keep the AFR's in line.

If we do vent to atmosphere the fuel head will keep supplying fuel as if all the air being used by the motor. Thus, one will end up with a lot of fuel being dumped down the intake during de-accel.

I suspect some CIS turbo race cars may have done this as an anti-lag strategy as it can turn the turbos hot side into a little jet turbine as the fuel hits the red hot area. Not good for turbo life on a street-able car.

I am rusty on this thread but an instant 2 psi sounds with a 5k shift sounds very low to me.

On my C2 Turbo my boost gage stayed pegged between sport shift. I also pulled instant .2 bar off idle and instant .5 bar off cruse.

I believe the stock 930 dump system can work well if in good working condition. I believe many are in need of service.

I have seen evidence in some of the tuner articles over the years that a couple of the well known old school tuners have actually modified them to stay open at idle and cruse only close on acceleration like I did my C2T style BOV. This allows the turbo to spin up at idle or on curse creating a reserve so to speak. Then the valve would only close with acceleration allowing for much faster boost onset. If I had a 930 that was still using the stock BOV, I would figure out how to do this. (I would also convert my WUR to vac-sensing to get the metering plate moving quicker.)

I like having a throtle bypass valve (de-accel valve). It provides some surge protection like the BOV dose. If the BOV fails it be the only thing to save one from blowing off a hose or O ring in the area after the turbo or worse yet, snaping a turbo shaft in half. Further, it helps keep the boost up between shifts. It should not restrain a motor from coming back to idle quickly.

Last edited by 911st; 11-05-2009 at 02:53 PM..
Old 11-05-2009, 02:51 PM
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