BOV Mounting: Hot Pipe Vs. Cold Pipe

[Driftless240]

'ello Ka-T's. I myself, plan on going Ka-T. I am going to piece my own "Kit" together. I also plan on making a custom FMIC; buy core, fabricate piping.

I have seen Blow off Valves Mounted on both the Hot Pipe and the Cold Pipe. Why would one post a BOV to the Cold vs. Hot or Hot vs. Cold. A majority that I have seen have mounted it to the Tubro Side of the piping, I was planning on doing the same, but just wanted to see why people would mount it on the other. Thanks for the help in advance.

Also I would like your opinion on Blow Off Valve:

~HKS Super Sequential~Greddy Type S (Purple One)

A BOV is a BOV to most but If I am going to be hearing it when I drive, I would I like to enjoy the sound of it. I cant decide which to go with because I enjoy both alotm just wanted to get your opinions while I was here speeking of BOV's. Thanx.

[S13FX]

Quote »Ideally the BOV should be after the intercooler and before the throttle body. The DSM cars have the perfect setup. Less stress on the BOV because it's sitting after the intercooler and away from the hot charged air of the turbo. Being closer to the throttle body will result in quicker throttle repsonse and less of a chance of compressor surge and thus less stress on the turbo itself.[/quote]When your throttle body slams shut a pressure wave is created right there and it travels backward through the system, then smacks into the turbo (surge).Putting the BOV right by the throttle body (where the pressure wave is created) is the most effective place.

I have my Bov on the first pipe running from the Intercooler on the cold side.

[Driftless240]

Thanks Mikie...

[jmhalder]

if you plan on going blow thru, i would mount it on the hot side... pull through, i would mount it on the cold side...

[daconkiftador]

Ive always heard/seen people running it on the hotpipe with no problems what so ever.. once my car is put back together thats where il be putting it.

[98240]

I run my bov off the hotpipe on the first pipe off the turbo. I have had no problems at all. I also had it on the hotpipe right by the intercooler. I was also running the blow thru setup.

[GEO]

umm.... if you mount it on the cold side.. what about all the air in the pipes after the bov.. like in the intercooler and on the hotside? Isn't it much better to release all the pressure off right after the turbo so ALL the excess air after the throttle bottle has shut can exit.

[myRed240]

I've got mine mounted on the hot side right after the turbo. I did this because I thought it would be better to release the air closest to the turbo and also to release the hotter air rather than air already cooled by the IC.

-Alex

[Chris@AMS]

That is the same way that I have done it. I am interested to hear everyones opinions and other facts however...

[Edub1]

When your throttle body slams shut a pressure wave is created right there and it travels backward through the system, then smacks into the turbo (surge).Putting the BOV right by the throttle body (where the pressure wave is created) is the most effective place.

I have my Bov on the first pipe running from the Intercooler on the cold side.

This is correct and I think it is how most manufactrers have it. The intake charge has mass and velocity as well as pressure. A hot pipe BOV can only vent pressure that has backtracked through the system and is about to surge or is surging the turbo. A cold pipe BOV will allow the turbo to naturally expell the moving charge just as if it is going through the motor. Think of a train switching tracks as opposed to having to back up.

[PapaSmurf2k3]

My Friend's WRX has the BOV mounted right after the turbo, and he's got a huge perrin FMIC. Because the BOV is mounted right next to the turbo, and signal is coming from intake manifold pressure, while spooling up to High PSI, the BOV kicks on sometimes, because its reading different pressures between pipe pressure and manifold pressure, possibly because of the pressure drop across the FMIC (im not really positive on that, thats just my best guess) I run mine on my cold pipe (blow through MAF) and dont have that problem. I vote cold pipe.

[SeanC]

i am sure you can argue this to death, along with the option of not havin a BOV which a lot o people do. if you are trying to minimize compressor surge and it works on both sides of the intercooler, then it does not really matter. i have mine on the hot pipe right before the transition to the lower pipe, mine is recirculated to the intake pipe before the turbo after the maf. when mine releases it sounds like a whip cracking. turbo xs r-34 BTW.

[hayaimoto]

Well BOV's are designed to "protect surging" to the turbocharger as well. Which in this case makes since to have it near the turbo unit, but most people mount it on the cold side becuase there is a larger amount of air mass and pressure flowing through the intake chamber. (plus it make more noise as well). Most people in Japan dont believe in BOV's as mush as we do here in the states, if the wastegate is properly sized there's nothing to worry about.

[hannibal]

Ive gone back and forth with this in my mind. I'm officially sticking with cold side now. Like S13FX said, when the throttle closes, the pressure build up starts at the TB and travels back thru the IC to the compressor outlet. So venting this pressure at the earliest point (closer to the TB) seems to be better.

[Fenvy]

how about 1 bov on cold side and 1 on the hot side? BAM!

[Swedish Mike]

Ive gone back and forth with this in my mind. I'm officially sticking with cold side now. Like S13FX said, when the throttle closes, the pressure build up starts at the TB and travels back thru the IC to the compressor outlet. So venting this pressure at the earliest point (closer to the TB) seems to be better.

This is the exact reason for mounting it close to TB, you don´t want the air to change flow direction. If you mount it at the hot side it need to change direction all the time.And cold side vs hot side doesn´t matter, the air will pass the IC and get cold anyway.

I heard this from an old rally engine tech many years ago and followed it since.Both ways will work but he measured thottle response time and wanted the air to flow in one direction.Some race cars even use IC´s made to flow in one direction.

Ok, shoot me....

[C-Kwik]

Turbo surge is not a function of a pressure wave. It has to do with the fact that there is almost zero airflow at any boost level. If you look at any turbo compressor map, zero airflow at any boost level will put you on the bad side of the surge line. This is all yhou need to prevent from occurring. Putting a BOV on either side of the IC, so long as it's functioning properly, will divert enough airflow to prevent surge. My own preference, particularly with an open vented BOV, would be to mount it on the hot side to reduce the amount of heat reaching the IC. For a recirculated system, there may be limitations in placement based on space, but I'd probably still have a preference for the hot side.

[WDRacing]

The best place for a BOV is as close as possible to the TB for the exact reasons already stated.

[boznuttz]

I'd like to see how many people have their BOV on the cold pipe near the throttle body with only an SAFC. On a pull or blow through setup, I wonder which had its drawbacks. I was really considering the hotside so i could run a blow through setup to avoid stalling issues. So anyone running an SAFC, please chime in as well please.

[Edub1]

I know the stock WRX has it on the cold side of the intercooler.

[WDRacing]

The Skyline also places it as close to the TB as possible. All of the Skylines...GTR included have them on the cold pipe.

[KATwo40]

Yet the SR has it on the SMIC...far far away from the TB.

I run a Greddy Type R (freakin' fire hydrant lookin' piece of crap) on the hot pipe, right at the FMIC. I still get a little bit of unloaded surge (no chirpy, just sounds like a typewriter), but I point my finger at the large compressor (T3/T04E), not the BOV placement.

Oh yeah, I run a blow-through MAF.

[Edub1]

I have a DSM BOV on the cold pipe. Sometimes it sounded like a high ptiched turkey. I can tell it was opening though cuz my AF would drop into the 10s.