BOV flutter with a BIG turbo
 

I know there are about 1,000 BOV flutter threads, trust me I've searched them all and still don't have an answer to my question. Please read below...

On my car I'm running the stock MAF/ECU with a GT35r. Originally when I installed the turbo I was using the JDM MR valve. I had no problems holding boost upto 24psi and there was no indication of BOV flutter. The only problem I experienced was a slight bucking on the highway in 5th gear with light throttle inputs.

Recently I upgraded my UICP from stock to a Buschur unit (awesome piece BTW) w/ a 1g style BOV flange, so the JDM MR BOV was replaced with a Forge BOV. The Forge came with 4 different springs and 2 shims.

I installed the new pipes & BOV with the softest spring, did a boost leak test and went for a quick test drive. The sound of the BOV is awesome but with the softest spring I was getting serious fluttering @ WOT in 3rd gear and higher. Whats happeing is I smash the gas at say 2k and around 4k I start to hear the BOV open and close, the boost needle bounces and it sounds like compressor surge... yeah its BOV flutter.

I called Forge and asked what they would recomend for my setup. The guy I spoke to suggested I used the yellow spring which is rated between 13-23psi and no shim to start off. This helped a little bit but I'm still getting flutter @ 4k but its in 4th gear now instead of 3rd like with the softer spring. So I went a head and tried all four of their springs with & w/o shims and nothing seems to work to eliminate the flutter.

has anyone experienced a similiar problem?

Man, that sounds like straight up compressor surge and not "bov flutter" to me. Think about it, how is the BOV going to "flutter" open and closed when it sees both the equivalent manifold pressure as well as the spring pressure. BOVs can have an effect on compressor surge as you can run soft springs and basically set them up to leak which obviously might allow just enough extra flow to prevent the surge.

Not only that but the situation you described is about as textbook as it comes for generating surge on a 35R. I still think that a proper surge ported compressor housing and not the bullet style will be your permanent fix. I can load the hell out of my car in 5th and as the boost comes up around 15 psi I can hear the compressor wheel start to surge a bit, but the ports do their job and there's no evidence of the surge at all other than a bit of sound (even still its not loud and you have to listen closely to hear what I'm describing).

I don't think its compressor surge for a couple of reasons. First and most importantly is that the sensation only started after I switched to the Forge BOV from the stock JDM MR unit. When I was running the stock JDM MR valve I got zero flutter at any RPM and only experienced compressor surge in 5th gear. Secondly is the fact that the sensation got better when I increased the stiffness of the spring. It went from happening in 3rd @ 4k to only happening in 4th and 5th @ 4k.

I don't understand WHY the BOV isn't staying shut when, like you mentioned, it is getting pressure on both sides. I'm using the stock BOV signal line as a reference and there is nothing else 'T' off it.

I just switch my tune back to the stock map and the car is still doing the same thing. So I'm 100% positive its not the tune. That makes me even more sure its not compressor surge either because the turbo was spooling slow as crap, yet it still happened @ 4k in 4th gear.

Does your turbo have a ported shroud? From the description it sounds exactly like compressor surge; at what RPM does the surging/fluttering stop?

the compressor cover I have has the bullet style ports, not the large slits like the garrett units.

I really don't think it compressor surge though, someone send me their garret style compressor cover to try out please, lol.

Dude, it IS compressor surge. There is no denying it. Well, you can deny it, but that won't change the fact that it IS compressor surge. The pressure pulses make the BOV open and close rapidly. Changing springs WILL have an effect on compressor surge, but no matter how many different setups you try, it may always be there.

As already stated, some people run the BOV soft to the point of leaking to get around surge. That is whole reason the "single spring mod" on the Greddy Type-S was so popular - basically is was set up so soft that it leaked, stopping the BOV flutter/compressor surge. . .

My suggestion - alter your driving style or get the other type of ported housing . . .

Good luck with it, I know from experience how frustrating it can be :(

EVOlutionary

So after all the **** I went through to get a bullet ported shroud my 35R will surge like that? Why do some people have this issue and others don't? My 2G DSM had it and I hated it but I learned to work around it. so basically the bullet ported shroud is ****?

Update.... After replacing the stock Intake with a Dejon Tools 4" intake to 3" for the MAF my car now surges slightly in 4th gear if you load it just right.... There is really no bucking as it is not that bad but there is the sound of a fluttering right before the turbo produces full boost. The odd thing is it didn't do it with the OEM intake pipe but with the bigger one it does. To anyone that has a 35R with a stock Intake pipe take that ***** off now and replace it ASAP spool is improved dramatically. I was told that a 35R won't really surge at 21-23psi more like 28+ but mine is surging at around 21psi..... The surging is noticable only if you listen for it really but it is there.