Lag after BPV Change?
11-11-2004, 05:14 PM
#13
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why would a lighter spring act faster? The stronger spring i have now
works faster than the lighter ones. I figure the stronger the spring, the faster it will be able to close when it loses the vacuum holding it open.
11-13-2004, 10:11 PM
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Reclusive speaks. . .
Think of the BPV spring as a safety valve, much like the wastegate, except without the N75K (that's for you, Tom). :`)
Certainly, the spring helps to close the BPV; a stiffer spring certainly works against manifold vacuum striving to open the valve, and the stiffer the spring, the faster it closes (time between vacuum and boost). Arguably, if you have a BIG turbo, lag (difference between vacuum and boost) welcomes the BPV's ability to close quickly despite the absence of vacuum (stiff spring) in order to build boost as quickly as possible.
I think the real discussion should focus on the volume of boost recirculated by the BPV. My Dahlback "super dump" is very fast acting (ear dyno) and has 1.5" I.D. orifices. I'll throw it on the MityVac to see what kind of vacuum is necessary to open it (some indication of spring "pressure").
Certainly, the spring helps to close the BPV; a stiffer spring certainly works against manifold vacuum striving to open the valve, and the stiffer the spring, the faster it closes (time between vacuum and boost). Arguably, if you have a BIG turbo, lag (difference between vacuum and boost) welcomes the BPV's ability to close quickly despite the absence of vacuum (stiff spring) in order to build boost as quickly as possible.
I think the real discussion should focus on the volume of boost recirculated by the BPV. My Dahlback "super dump" is very fast acting (ear dyno) and has 1.5" I.D. orifices. I'll throw it on the MityVac to see what kind of vacuum is necessary to open it (some indication of spring "pressure").
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