Hi,

Sorry for the ignorance, but I was talking to a friend with a WRX and he was telling me he didn't want to install a blow off valve on his car because he wanted to retain the pressure of the turbo. He didn't say it that way exactly but that's the best way I could put it, he just said that he'd rather not have one.

Can a blow-off valve ever hurt the perforance of a turbo/sc engine?

thanks

 

High boost + no BOV = damaged mafs and compressor blades.

 

plus if the BOV isnt on properly you can lose PSI

 

besides, that's half the fun, that pshhh sound... i opened up the greddy bov last night and good lord, that thing doesnt stop pshhhhing when im goin down the highway

 

Actually not have a BOV on a boosted car will hurt performance and is damaging your compresor wheels. The whole point of the BOV is to release all the pressure(pssshhh)that has built up from the turbo(or s/c)after you let of the throttle quickly to shift gears.

It is possible to have a boosted car w/out a BOV but then you're gonna have to ease off the throttle very slowly after WOT each time you shift gears. So forget about racing w/out the bov.

 

realistically a by pass valve is better. It redirects air back into the intake stream. In a way Blow off valves is a showoff mod. a bypass valve is better then a blow off valve. Sometimes the BOV will cause probs on cars with Mass air flow sensors. oh well.....

 

Isnt there a way to redirect the air from a bov back into the intake stream?

 

Thanks for all of the replies. There was this really old Mitsu Galant VR-4, it looked like it was falling apart. But as it passed by, it did a show off "pshh" sound. Even if it may not always indicate a fast car, it sounds cool nonetheless.

 

I've read on the 240 board that HKS SSQVs will blow out of the car under high boost..

 

Do your BOV's open in between normal driving shifts?
Mine doesn't until after 3K rpm's. I kinda feel that it should open earlier but 5th gens stall. Is it damaging my SC by not opening at low rpm's (no boost)?
to answer the original post... unless your BOV is open under WOT, you're not losing performance.

 

yes just put a tube on it back to the intake like mine.


The only way it's gonna hurt your perfomance numbers is if you got it open while your boosting, and at that point it's just your fault.

 

the bov only opens under load, when letting off the gas/shifting, meaning when it actually builds pressure. It's only going to make noise after 3k rpm because that's only when boost is being produced..

 

Ok, so I have my Greddy Type-S set to its loosest setting without the car stalling so that I can pretty much make sure it releasing pressure even under the lowest throttle, I really can't afford messing up my compressor blades. From under the hood, the BOV functions like it should, during idle it vents a little bit of air and under throttle it closes and then reopens when let off. From my boost gauge I consistently see about 10 psi at redline with my 3.33" pulley. Would recirculating the air back into the air or tightening the BOV so that it doesn't vent any air at idle be better at the track? I doubt the BOV tightening would help, but maybe one of you guys might know.

-Ben

 

what do you mean blow out of the car?

 

BLows off the pipe and thru the hood..

 

That sounds like it needs to be installed better.

 

the BOV wont blow off the pipe unless it was installed improperly. Its held in by a steel snap ring. You'd need ALOT of boost to do that.

 

What he was probably referring to was blow-off vs bypass valve. A blow off valve vents to atmosphere, thats why you hear the sound, and it can make MAF readings inaccurate. The maf reads a certain amoutn of air coming in, and in turn gives a certain amount of fuel, but SOME of that air gets blown off into atmosphere, meaning there is less air going into the cylinder, meaning a lower AFR, making the car run a little richer. A bypass valve vents the air right back into the intake tract, so the MAF reading isn't out of whack. But you don't get the nice sound.

 

Some cars come setup with the bypass valve from the factory. The Audi S4 is designed this way.

 

I took my blow off valve, and made a piece that goes from that back into the intake, and guess what...You still here it.

 

A well designed system will always have a bypass of some type whether it is bypass valve or BOV. This is to reduce backpressure when the TB closes which slows down the turbo and can damage it. BOV's are like turbomax said more showy. The HKS SSQBOV does have an optional attachment that allows you to attach a hose to feedback to the intake side to avoid the super rich condition that happens on MAF systems. In any case turbo systems SHOULD have a valve ... even if it is a plastic one that is provided on some cars.

 

The WRX comes with a recirculating BOV (same thing as by-pass valve?) that helps keep the turbo spooled. So, yes, by adding an aftermarket atmospheric BOV he could end up hurting his performance.

 

MOst of it not all factory cars will come with a bypass valve vs a blow off valve. thats why i said a blow off valve is more a showoff thing, but i still like it...heeh