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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
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Originally Posted by cole930 View Post
There is not a type of BOV that is made to operate that way. 911st simply re-plumbed a 964 style BOV to operate that way. Keith is a great resource of information on 930's and I'm sure he would be glad to tell you how he did it.

O'l Cole,

Mr. Flintsone here (aka Mr. Gimpy). I can't resist...let me prime the thought pump.

Take a "modern" piston-style (not diaphram) BOV as many of us use. With the vacuum line attached to the intake manifold post-TB, and swapping out the stock 14 lb. spring with something in the 2 lb. range, and given that the intake manifold will produce something like 200 millibars of vacuum when at steady no-load cruise, that's just enough vacuum to overcome the spring tension and open the valve...allowing the turbo to freewheel. Now, stomp in the throttle and the vacuum pretty much goes away with the throttle plate wide open, and the 2 lb spring closes the piston. And as boost begins to build, that vacuum line to the intake manifold now becomes pressurized, adding to the spring tenson on top of the piston to keep it closed until you take your foot off and the vacuum spikes back up to open the valve and vent the boost pressure that is residing in the IC/pre-throttle body intake.

All theory of course, and since my BOV is buried beyond easy access I'm not inclined to pull the spring out and stuff in a 2 lb. spring to test this. But hey....could actually work.
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 03-25-2010, 02:24 PM
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