Thread: BOV orientation
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billjam billjam is offline
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Location: Perth, Western Australia
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Originally Posted by mark houghton View Post
With this understanding, one need only determine how soft the spring needs to be. BJ: As soft as possible. My BOV came with a stiff spring to hold against about 1.0 bar, and shims to make it even stiffer if wanted....because most people depend on the spring tension only to keep it closed. Theoretically, the spring tension in the above configuration would need to be only slightly less (inversely) as the amount of vacuum available from the throttle body at steady state that small amount of vaccum can overcome the tension and open the valve.

Just thought I would spend the evening rambling. Does anyone know how many inches of mercury vacuum is generated in closed throttle plate situations vs. partially open steady cruise throttle positions? Or does anyone think this is all bogus and not worth the effort of fine-tuning?
I recently modified my BOV after following the thread you referred to.
I set it up with as little spring pressure as possible so that the slightest vacuum on the top side of piston would keep the valve open. When driving, I couldn't tell the difference between having more or less spring pressure or having the valve upright or horizontal!
Post 28 in that thread is what it all boils down to ... these little 20mm BOVs can't pass enough air to make a noticeable difference IMHO. I can fart more powerfully

As far as vaccum readings are concerned, the red line is what I usually see at light throttle cruise and the green line is throttle closed on over-run.

1988 Carrera - 3.6 engine (with ITBs, COPs, MS3X) and a whole set of turbo body panels waiting in the attic.
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Memories: '68 912, '72 911T, '80 911SC, '84 911, '85 930, '86 930, '87 911
Old 12-07-2009, 09:01 PM
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