Ok, I have been searching for awhile though the site for info on this and there is really a bunch of scattered information on this subject. I am hoping this will be a sticky for those with questions on this and this will have all the info in one place. Personally I have always used the BOV on the hot/pressure pipe but I have been hearing those that have used a BOV on the cold/ boost pipe. Since I have not had any experience with this particular set up would someone please list the pro's and cons, advantages and disadvantages, the different types of BOV's-which ones would be best on which side and perhaps get this to be a sticky for quick reference. Because I have not done it on the cold pipe before I am unsure what exactly I can tell my customers on this issue. Thank you all for the help and the information that will be given.
Modified by ChristianKustomz at 1:23 AM 9/7/2009
BOV placement HOT or COLD
Re: BOV placement HOT or COLD (ChristianKustomz)
put it on the hot side, as close to the turbo as possible. also run the vacuum line from the bov directly to the throttle body- if you T it off to something else, response is diminished. Use the correct size line too.
Reasoning: Your bypass valve is supposed to bypass unwanted pressure in the plumbing. If the bypass is on the cold side, then all of the high pressure from the turbo to the bypass has to flow through the intercooler to get out, which means it the venting will be slower, more gradual, not as sharp and not as quick. People will say this "keeps the air moving in the right direction"- however, air is always flowing into the engine, even at idle or after you let off and the throttle body shuts, the engine still breathes. The purpose of the bypass isnt to keep the engine breathing its to prevent COMPRESSOR SURGE. By placing the bov on the hot side:
the turbo gets a fast-as-possible response for relief of compressor surge
the release is more sharp, and faster, which on a maf car, is a large benefit (Due to the way the ECU cuts fuel) you will note that cars with bovs on the cold side, even a ssqv, will tend to backfire under light throttle conditions... because the ecu cuts the fuel but idle falls low enough for it to come back in with the bov still hanging open... and POP!
Air density at constant temp is related to pressure. whether the plumbing releases pressure on the cold side or hot side doesnt make a difference- the turbo still has to re-compress the column of air when you step on the gas. the air doesn't "keep moving" any more or less whichever side its on- the engine is always breathing, and unless you are shifting with the throttle body open, the column is going to lose its increased pressure ratio.
oh, i still put some bov on the cold side, just for looks though. they looks cool right there by the throttle body. And they are quieter, more subtle. And the vacuum line is shorter, which means it opens even easier. Yes it backfires unnecessarily and yes the compressor surges slightly more than it should but... LOL it still serves its purpose.
Reasoning: Your bypass valve is supposed to bypass unwanted pressure in the plumbing. If the bypass is on the cold side, then all of the high pressure from the turbo to the bypass has to flow through the intercooler to get out, which means it the venting will be slower, more gradual, not as sharp and not as quick. People will say this "keeps the air moving in the right direction"- however, air is always flowing into the engine, even at idle or after you let off and the throttle body shuts, the engine still breathes. The purpose of the bypass isnt to keep the engine breathing its to prevent COMPRESSOR SURGE. By placing the bov on the hot side:
the turbo gets a fast-as-possible response for relief of compressor surge
the release is more sharp, and faster, which on a maf car, is a large benefit (Due to the way the ECU cuts fuel) you will note that cars with bovs on the cold side, even a ssqv, will tend to backfire under light throttle conditions... because the ecu cuts the fuel but idle falls low enough for it to come back in with the bov still hanging open... and POP!
Air density at constant temp is related to pressure. whether the plumbing releases pressure on the cold side or hot side doesnt make a difference- the turbo still has to re-compress the column of air when you step on the gas. the air doesn't "keep moving" any more or less whichever side its on- the engine is always breathing, and unless you are shifting with the throttle body open, the column is going to lose its increased pressure ratio.
oh, i still put some bov on the cold side, just for looks though. they looks cool right there by the throttle body. And they are quieter, more subtle. And the vacuum line is shorter, which means it opens even easier. Yes it backfires unnecessarily and yes the compressor surges slightly more than it should but... LOL it still serves its purpose.
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the converted
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Re: BOV placement HOT or COLD (kingtal0n)
It actually doesn't make a difference where you put the BOV. What it is trying to do is prevent a pressure wave from reverberating back to the turbo, so if your putting it near the throttle body, it won't get a chance to start, where as if you put it back near the turbo on the hot pipe, your just releasing it off to atmosphere before it travels all the way back.
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ChristianKustomz
Re: BOV placement HOT or COLD (the converted)
Awesome job! Thanks a load. This was a great post. Hopefully this can get stickied so it can be accessible for eveyone. Plus I learned a thing or two also. Thanks again