Stopping Your BOV From Leaking - A How To

[benl1981]

Does the R33 GTR BOV have this Bleed hole. If it doesnt I might replace with one of those, so I get the response plus the BOV functioning properly if this is indeed an issue.

[Yeedogga]

I had a hole-blocked & squashed stock BOV on my R33 and it was a pain in the arse. Boost did come on nicely and it did flutter a bit on low RPM let off but it was so jerky in throttle transition i had to take it off and replace it with another stocker.

If anyone wants it to play with PM me its yours.

Edited September 29, 2009 by Yeedogga

[karma_syke]

So whats the final verdict on this? we shouldn't do it because if you do the valve only opens partly? does the boost performance outweigh this con? any proof in the boost performance?

[89CAL]

If you think of it as an externally piloted relief valve (if you've done hydraulics this will make sense) then it shouldn't matter if that port is blocked off. There is going to be say 10psi acting on the valve from the bottom (IC pipe boost) and 10psi acting on the top (from manifold to topof BOV) and spring tension at top as well

So the way I see it the vacuum line is the external pilot and when you close the throttle body you will have a negative pressure on the top of the BOV and 10psi at the bottom overcoming spring tension

The little hole shouldn't theoretically make much of a difference to this aspect (the BOV acting as a relief valve when throttle body is closed) at all. Really all that little hole is Doing is drawing air back to the intake which is always under vacuum, which I guess could help raise the valve by adding a negative pressure between the valve seat and internals of the BOV (if that makes sense) perhaps this just speeds up response in the quick moment between positive and negative manifold pressures. Drawings would make this easier lol

Edited February 25, 2011 by 89CAL

[karma_syke]

i can't remember, does the plumb back enter before or after the compressor?

if its after then the pressure in the plumb back pipe would be the same as the boost pressure, and therefore it wouldn't be 'leaking' air at all, just simply acting as an equalizers, and when the throttle plate closes that column of rushing air bounces off it, hits the diaphragm of the bov, overcomes the spring tension, thus opening and giving that pressure wave an alternate route. (other than directly back through the intercooler and back at the turbo compressor)

if the plumb back pipe feeds in before the compressor, then i would imagine there could possibly be a significant boost leak because there would be a large vacuum created before the turbo compressor and it would be effectively sucking the air from the bov pipeline, this low pressure created in the bov plumb back pipeline coupled with the high boost pressure in the crossover bar would accentuate the 'leak' (its not really a leak cuz it goes straight back into the turbo again).

thus the air is constantly doing a giant loop an your losing turbo efficiency.

whether or not the 'leak' is really significant or not i have no idea, i suppose it would be good if we saw a dyno chart, where the suggested mod is the only variable.

edit: imagine a mythbusters style for cars where they check shit like this out, i'd watch it.

Edited February 25, 2011 by karma_syke

[89CAL]

bov return enters in the intake pipe (rubber ribbed hose on standard skyline setup)

This vacuum acts to pull the valve up but also pull it down (in the chamber I'm not sure if theres any effective area on the top side of the valve that it can effectivly pull down)

If this is the case then both pressures would basically cancel each other out, depending on surface area etc.

If not then I guess the spring is in place to compensate this, the small hole I dont think would leak enough pressure through to make a difference for this