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Blow off or Bypass Valves?

Old 06-09-2007, 09:17 PM
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Blow off or Bypass Valves?

I was wondering what the difference is between a Blow Off valve and a Bypass valve? Does one give better performance than the other, or whats the deal?
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Old 07-05-2007, 12:54 AM
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virtually a bypass valve is a vacuum-actuated valve that releases pressure in the intake and recirculates it back to the end of the intake where there is no preasure. think of it as a recirculating pressure valve that realeases the pressure when your foot is off the throtle.

a blow off valve is the same thing and same idea, but instead the pressure is dumped into the atmosphere, thus causing the blow off sound that you hear. some cars, such as subarus and vw's don't need blow off valves on the stock turbo setup because atmospheric dump causes the cars to run rich as screws with the MAF sensors. Most noobs and ricers get BOV's for their stock turbo setups when they don't make enough pressure to be needing it. those idiots just liket he pSHHHHHHh sound.

most cars with turbo charged engines have stock bypass valves.
for the most part, bypass valves are popular in the after market scene. most of the pressurized release valves are all atmospheric dumps aka BOV's.

but at the end oft he day, you don't need a BOV unless you are running higher than stock boost levels or if you are turboing an NA car and have no choice but aftermarket.


i would be of more help if i knew what you drove.

hope this helps though.

Last edited by 2007scooby; 07-05-2007 at 01:00 AM.
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Old 08-07-2007, 05:32 PM
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Hey man thanks it does help quite abit but im not quite old enough to drive yet so i dont have a car, but one more question. So if your running low PSI you only need a Bypass Valve but you need a Blow off valve when your running high PSI so your Turbo doesnt blow up right??
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Old 10-25-2007, 06:38 PM
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Chris as an FYI usually engine failures don't necessarily mean the turbos "blow up."

With the G35/350Z's VQ35 engine, it starts out life as a normally aspirated engine. Guys who want to be a bit more on the safe (and have the money) side will drop their compression ratios (low compression pistons), enrichen the air:fuel ratio (upgrade fuel injectors, fuel pump, computer), change out to forged internals (connecting rods), and studs.

Engine failures that I've heard about in the VQ's after force feeding them usually are blown head gaskets, broken rods, an occasional hole in the block, fried pistons depending on the particular FI application. The turbo(s) may fail due to lack of oil or oil running too hot to sufficiently cool them. While rebuilding a turbo sucks, IMHO it's more about protecting your engine than the turbos.
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Old 10-24-2008, 05:04 PM
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They are both essentially the same thing. The major difference I believe, is that aftermarket valves are made for higher boost pressures (and for turbocharged-initially normally aspirated cars) like 2007scooby has already mentioned. But they do the same thing: take redirected air from the charge pipe (intercooler pipe) that would be flowing backwards and releases it elsewhere, atmosphere or intake system.

Turbos will not blow up but they will get damaged if the returning airflow (that's redirected from the throttle body) interferes with the initial direction of the airflow coming out of the turbo. So what a blow off valve will do is either dump it out into the atmosphere "blowing off" OR recirculate it back into the intake by the way of some tubing that will NOT interfere with the directional flow coming out of the turbo. Hope I didn't confuse you.
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