*More consice explanation of above*
BOV on cold pipe = less lag between shifts. How much less lag is debatable.

 

Only downfall to this is A) the blow off valve does NOT and will NOT regulate boost pressure, it simply relieves it. The air on the bottom side isnt forcing it open, it gets sucked open by dropping the throttle or a combination of both. B) Im not a math major or anything but if you boosting at 12psi and drop the throttle, what pressures are now within the piping trying to blow stuff apart? 2x's 3 x's the original 12. This pressure is created all the way back down your pipes, through your intercooler, back to the blow off valve, no? Just trying to logically think this through.

 

Well when you drop the throttle and are at full boost (spooled), the engine is taking in less air, and the compressor is still putting out the same amount. Wouldnt it make sense to have the BOV release the pressure as close to the compressor as possible? Or am I thinking of a wastegate? I guess I'm not really sure of the difference in the workings of the two.

To me, I always thought a wastegate opened when there was too much boost ("regulating" the pressure) and still on the throttle, and the BOV was there for when you shifted and the engine suddenly didnt need all that air because the throttle was closed.

... Now that I think about it, cold side would make more sense because it is closer to the throttle butterfly, making it a faster release, and allowing the turbo to stay spooled for when you got back on the gas. I guess I kind of answered my own question there didn't I hehe.

 

Just to complete your answer, Jinx, the wastegate does regulate the boost pressure. But, it does so by letting exhaust gas go around the turbo instead of through through it. The wastegate happens completely on the exhaust side, while the bov is strictly on the fresh air side.

To hit Tnathe's math problem... The bov has a spring that holds it closed with a force of around 8psi worth (assumption, approx). When you're boosting 12psi (or 20 or whatever) the valve sees 12psi on the bottom, but also 12psi on the top because of the vacuum hose to the intake manifold. So, with those pressures equal, the bov is held closed by the force of the spring. When you close the throttle, the intake manifold hits vacuum of around -10 psig. So now, you have 12psi pushing up against bov, 8psi worth of spring pushing back, and now 10psi of vacuum pulling against it. 12+10 is greater than 8, so the bov opens. It will close again once the manifold is boosted again, or the pressure equation equalizes.

 

epstein.. s14 is like that bc that is where the stock bov location is on a s14 motor.. just like why it is in he drivers fender on a s13 kit. greddy for some crazy reason thinks that you will reuse your stock recirc valve... and that is their factory location... but your explenation about air flow direction is very good... but I say fuck bov's... just run a port shrouded turbo and problem solved that is the way tim ran punisher until i got a chance to put in a flange. 0 surge even under 27 psi on a gt35r..

martin
xat

 

what is this "port shrouded turbo" you speak of. Never heard of such a thing. I LOVE the sound compressor surge, too bad its not good for Mr. turbo or I would be running it with nothing to vent pressure.

 

mines on the cold side, it works perfect

 

http://www.atpturbo.com/Merchant2/gr...30R-225225.jpg

Slits around the copmressor wheel.

 

This is the way it was explained to me by a friend. You want to put the bov on the hot side close to the throttle body. The reason is as the pressure goes through the fmic it lowers slightly and then as it hits the other side the pressure will increase and as soon as you let off the gas the throttle will have the most pressure at that point so the bov will release it immediately which reduce the strain on the turbo..

 

throttle body on hotside i think u mean cold