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Old 09-09-2003, 09:38 PM
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Join Date: Nov 1999
Location: Brisbane, Australia, Q
Cobra Make, Engine: Contemporary CCX3117 427FE
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Mike - sorry for the delay in replying. I've been minding my sister's house (zoo), and they don't have a computer.....

How can I cope under such adversity?!?

I can't remember exactly how the Procharger was set up on Garrett's car, but I think he had the serpentine belt.... In that case, while it would be nice to have even the smallest Bosch blow-off valve, it isn't absolutely necessary. Any pressurised air that hits the closed throttle and rebounds back towards the blower needs to be vented to prevent spiking the blower and potentially damaging the impeller and bearings. With moderate boost and a serpentine belt, the belt will simply slip on deceleration. This means that the impeller doesn't cop much abuse.

Now - the function of a blow-off valve is purely to dump the pressurised air under closed throttle. This is all they do. They simply get a signal from the manifold, and as soon as there's vacuum in the manifold, it draws the valve / piston inside the blow-off open. Boost control is done via a wastegate in a turbo application, or you can do some tricky boost control via Motec, Autronic and other good ECUs with a blower.

Garretts car - is it running MAP or MAF? If MAF, you'll have to see if it's mounted before or after the blower. Generally, they're mounted before. In this case, the ECU has used the Mass Air value to determine fuel injector pulse. If you vent that pressurised air on deceleration, the ECU will still inject LOTS of fuel because the MAF "read" a lot of air going past. You would have to run a hose from the BOV to somewhere between the MAF and blower so that the air is recirculated. A happy by-product of this is that you don't get the racer "WHOOOOSH" when you back off. My car isn't all that noticeable when you back off, but Scott should have his car in Fast and Furious 3 !!!!! He came up along side my friend's SS Impala and boosted it then backed off - the blow-off valve nearly scared the sh!t out of me.....

With more boost, I would definitely fit a BOV. Almost without exception, they will all work OK. It's a personal preference thing as to whether he would want the billet look, anodised look, or cast alloy

With blowers, you want the BOV pretty close to the blower. If he has an intercooler, definitely between the blower and intercooler. Turbos are the other way around....

Jeez - it would have been quicker for me to just pick up the phone and call you rather than type all this out!
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