blow-off valves

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what are the loudest and the best blow-off valves?

posted by  silvia_star


posted by  CarEXPERT

My stomac actually hurts now from laughing at that.

posted by  DodgeRida67

back on topic..GReddy and TurboXS probly have the loudest..Hks isnt too loud but there pretty pricey

posted by  Eclipse_2004

really? can i buy your butthole to put in as my blow-off valve? :laughing: how much do you want for it? :laughing: ill give you a nickel for it :fu:

posted by  silvia_star

well, i am not really sure about the prices of Blow off valves...but i would recommend HKS...they sound so mean on my friends' EVO and Silvia. Pretty loud!

posted by  nissanTFsx

yea,... i am thinking of getting a HKS BOV on my EVO too... :thumbs:

posted by  newuser03


I dont mind if i get flamed for this, but please include an answer in you flaming.

Im a student right now, i just finished learning about audio, thanks to thunderbird. Now im starting to get more involved under the hood, so could someone please explain to me the whole blow off valve and its parts, or at least point me to a site that will help me. I'm trying to learn about manifold, headers, exhaust, and all that jazz. thanks

posted by  Stem

The blow off valve is basically generally with a turbocharger and you should know that a turbo gets the air from the atmoshphere and compresses it to a pressure that is more than the atomosphere and gives it to your engine. So a turbo does this by spinning the turbine and sucking in air and compressing it when you give it throttle. But when you give it throttle and imedietly let off the gas, the throttle plates on th throttle body closes very fast but the turbo is still spinning from it momentum so the pressurelized air is still coming up the intake piping but Remember that the throttle plates are closed so the air will be forced back to the turbo and can damage the turbines so there is a blow off valve that is on the intake piping near the throttle plates so when the pressurelized air bounces off the plates, the blow off valve opens and let the pressurelized air out so it wont go back to the turbo. Thats basically it

posted by  CarEXPERT

im actually gonna give carexpert some credit for not doing a bad job at all at the explanation......... but a few corrections.

1) the BOV doesn't need to be next to the throttle, just somewhere along the way from the turbo to the throttle. location is optional (can even have 2 if u feel confused).

2) in very simple words, BOV's just get rid of excess air in the intake route in order to prevent backspin (reverse spin, which causes distortion and heavy stress = VERY bad) on the turbo.

3) superchargers can also equip BOV's (usually referred to as bypasses on superchargers, but they do the same, and are mostly optional for certain reasons).

posted by  Inygknok

Why thank you very much i completely understand. Thanks for not flaming me too.

Also, if you have a turbo, but with no BOV, will it.... 'kill' the turbo, or at least damage it? Also whats the intercooler for? :mrgreen:

posted by  Stem

Someone correct me of I'm wrong. But no, you shouldn't use a turbo w/out a blow off valve. I can imagine the compressor surge would be pretty harsh on the turbo, thus shortening the life of it by a great deal. Compressor surge can also happen w/a blow off valve depending on how much it is tigthened.

An intercooler is just what it sounds like. In laymans terms, it cools the air that your car is takin' in. Most turbo cars are intercooled, but the location varies (side mount - like on 300zx's, front mount - like on srt4's, and top mount - like on STi's).

Also not w/regards to your blow off valve, that some (depending on the car) must be able to be recirculated.

posted by  SpdRcrChk

You can also go here and read the job of the Intercooler:

posted by  car_crazy89

You'd be wrong on a couple of points. The internet has a lot of folklore.

You don't need a blow off valve if setup properly. The blow off valve prevents stall flutter.

Yes recirculating valves enable the ECU to keep track of the fueling and unlike blow off valves do not leak crank case fumes to atmosphere.

posted by  Wally

Then, I must say I've yet to see any high performance setups (factory, aftermarket, multi-million dollar racing, aircraft, or otherwise) that were done "properly".

Recirculating BOV's are necessary on certain fuel injection systems for the purpose of the ECU tracking the air. But, depending upon the type of fuel injection system and the location of the sensors, a recirculating BOV may not be necessary at all (an intake manifold "speed-density" based system for instance).

posted by  Bino

I have a feeling that what you're referring to as stall flutter, is the same thing as compressor surge. IIRC it's caused by pressure not being released and thus air is sent back into the turbo and causing the wheel to stall or spin in the opposite direction. It's the sound that's often mistaken for a blow off valve .... the "ch-ch-ch-ch" sound. And from what I understand, compressor surge shortens the life of a turbo. Even cars that come turbocharged from factory use some type of blow off valve (for example: SRT4's, and Eclipses), whether recirculated or atmospheric. Whether a blow off valve needs to be recirculated or not depends on the car. From what I understand, those cars that require a BOV to be recirculated are those that use a MAF sensor as opposed to a MAP sensor. Please note, that....I'm not saying it can't be done sans a BOV, but I would say that it would be safer/wiser to use one

As far as the Original question is concerned....

I agree w/what someone posted before. I believe that the HKS SSQ and the Greddy Type S blow off valves are known to be quite loud. WHen looking for a blow off valve, preferring something loud over something more efficient, however, would not be the road I'd choose. I'd probably look for which BOV is not known to leak, or cause compressor surge. I've had a greddy type S and I currently have a blitz DD. But to be quite frank, I'd rather have an HKS Racing BOV, or a Greddy Type R, Greddy Type RS or a Tial.

Silvia Star you might want to try doing a search online to learn how these items work. I strongly recommend

posted by  SpdRcrChk

All this talk about turbos is making me want a car with one...god I miss my 1988 Chrysler LeBaron :oops:

posted by  FordFromHell351

I dont know much about this topic (havent really done any tuner stuff) but my friend has a 1995 Honda Accord with a B16 VTECH transplant and he uses a Greddy BOV w/a Greddy stage 1 turbo kit.

posted by  FordFromHell351's Vtec not vtech, no H. ;)

I'm sure the greddy BOV your friend uses is a type S. They're notorious for being a little loud, as are the HKS SSQ. Tell you what though, loud or not they do the job.

posted by  SpdRcrChk

no, i just want to know which one is the loudest and best. people say greddy is gay. people say hks is the best and loudest but im not so sure.

posted by  silvia_star

Some people would say blow off valves are gay, no matter what the brand. :wink2:

posted by  Wally

If they prevent my $600 turbo from reversing its turbine at 130,000 rpm... I can live with that badge... :wink2:

posted by  Bino

Somehow i don't think the turbine nor the compressor impellor is going to reverse when the throttle plate snaps shut. All that's going tp happen is the boundary layer on the impellor blades is going to collapse from the sharp increase in static pressure and pumping cease. On top of this the exhaust flow will be be zip because the volumetric efficiency will be zip, so very little turbine contribution.

posted by  Wally

I can't believe u people are still arguing this.


Anyway.....loudest and best, go w/greddy and hks. the greddy type R blow off valve and the type RS are probably the best in their line up and the type S is probably the loudest. HKS SSQ is very loud too, but by far not the best in their line up. The HKS RACING BOV is probably the best.

Who cares if it's loud? You should care more about it's functionality.

posted by  SpdRcrChk

I'm not arguing, just giving some fact in a sea of fiction.

Besides BOVs are so passe. The hip happening thing is screamer pipes. :smoke: :wink2:

posted by  Wally

Isn't that the point of a forum?

I thought you couldn't believe it was still being argued, and then you try and say "do this". So now that you've said this should everyone stop arguing? You're presenting an opinion which may or may not be the same as other people's. These other people then have a right of reply ... hence a forum discussion.

Who's arguing now? The question was asked which was the best/loudest. Now you're saying that the question is wrong?... sounds like sparking argument to me.

I'm sorry if I've got this wrong, but it just annoys me when you say you can't believe it's being argued, and then throw a contradictory opinion in. Does that mean that you're allowed to put your opinion in, but others aren't?

posted by  windsonian

Well... given that they're connected... I'm entitled to agree that one will not happen w/o the other.

Every article I've read for the justified use of a BOV states that the spike in pressure from closing the throttle will rapidly decelerate and in many times stop the impellor/turbine rotation. The forces on the center shaft are huge due to the rapid deceleration of the turbine can cause excess center-bearing wear or possible shaft failure.

I find your logic very difficult to believe when racing teams that depend heavily upon the transient response of their turbocharger system continue to use BOV's. It would be very beneficial to not vent all of that previously compressed air to the atomsphere. If you can avoid venting the already compressed air... the system will spool much quicker once on the throttle... and yet the rallye cars and drag racers still use them religiously.

And... I'd love to drive a car with a vent-to-atmosphere waste-gate (screamer pipe)... Perhaps I'll have to try it sometime...

posted by  Bino

For every "raceteam" that uses a BOV, I'm sure you'll more that don't.

As far as rapid decelleration of the impellor, I'd be be interested if you would point me to a legit site that argues that the impellor will stop due to a reversion wave? I'd like to ask them about it for my own edification.

IMHO a bypass valve serves two noteable purposes:

it indeed lowers the transient pressure;

but it also allows continued flow to take place so that the boundary layer on the blade contours does not collapse. It is not the impellor that stalls (it is already winding down because the exhaust flow has dropped), it is the air flow that stalls. And when a mixed flow fan stops pumping it needs very little power to keep it spinning, becuase it isn't doing any work to speak of.

When you look at a compressor map you will note the stall region on the left and the choke area on the right. The stall referred to is where the surge takes place, not where a mechanical siezure occurs.
If you do some more reading you will also notice some of the performance engines use an expandable joiner on the boost pipe to absorb some of the spike.

A bypass valve also has a minor benefit in allowing lower enthalpy air to be introduced into the compressor than if it was all outside air.

I should also add that for the static pressure to rise as it does, the velocity pressure must drop. Because the velocity pressure drops the flow also drops, so any reverse flow will be substantially reduced, just ask Bernoulli.

posted by  Wally

Well, if nothing else this thread will get my books out of moth balls. Bernoulli and I have been quite well acquainted... but we haven't chatted in a while. I'll have to look him up again when I have a minute.

posted by  Bino

HKS super sequential blow off iz the nicest ive ever seen so far.. screw GReddy lolz

posted by  4g63

Does anybody know anything about turbonetics blow-off valves, specifically the new "raptor"?

posted by  Accord_Man

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