BOV Flutter
 

I got a question, what causes BOV flutter between two different turbos. I used to have a Mitsubishi T25 turbo setup with a Turbo XS BOV. This setup didn't flutter at all. When I changed to a T3 setup, my BOV flutters like a mofo. Even though I try to install it with a lighter spring it still flutters. What causes this?

less boost to help the diaphragm or piston at a given rpm maybe?

I think he means flutter at idle.

I think he means flutter on lift, or the BOV is lagging to open.

No flutter at idle. With my current T3 it flutters everytime when I shift. When I had my old mitsu T25, it would never flutter.

I'm assuming that since the T3 is like 30 million times larger than the T25, it spools a lot less at lower rpms causing the flutter (less boost at a given lower rpm). The BOV's lightest setting might still be to heavy during light boost. Therefore, the only way that I might fix this is to find a lighter spring, but might cause other problems such as leaking during idle. Please correct me if I'm wrong.

yes, and I have the same problem with my TurboXS. Flutters at low boost/low rpm doesnt at higher rpm.

Its all about how fast vacuum builds to pull the valve open.

I already cut off 3 coils and it did help a little, doesn't flutter as much. Frackin BOV, I'm gonna try cut the spring more to make it smaller. See if that helps.

Ok, cut off as much coils that I could from the spring before it started to leak at idle. Installed some washers to prevent it from leaking at idle. BOV now doesn't flutter on low boost. Only on high boost does it flutter. Makes me think the BOV that I have is undersized for my application. Damn sucks.

Only 1 way to solve this flutter..... turn up the boost and hit full boost all the time ;)

Ha ha, I don't really feel like damaging my turbo since the BOV flutters on high boost. I noticed that with the T3 turbo set up the BOV isn't as loud as the T25. I really like it quiet like this. I may change my BOV to something different such as the knockoff greddy's since people here are running it without the flutter.

How much does yours flutter?

Is it like a long lasting flutter or is it like a second of flutter and then it releases normally?

have you tried dismantling ur valve and just making sure it isnt binding?

Bailey twin piston dump valves are designed to stop flutter at tick over I think.

On high boost, the BOV flutters for a good 2 seconds then I don't hear anything after that (like BOV valve is closed, but I know its not). Noticed that sometimes on low boost it flutters for about a second then opens regular. I've taken the BOV apart many times, oiled it and made sure there was no binding. It operates smooth. I just purchased one of those Greddy knockoffs on ebay and see if that relieves the problem. Seems like the BOV ports are a lot larger on the Greddy than the turbo xs, plus, it was only $35 with everything I need to install it. Can't beat that!!

By 'flutter' you mean air coming back out of the turbo? i.e. turkey-sound from the turbo when you close the throttle? If it's going for seconds, then it's not just the momentum of the turbo.

I've noticed on my FM BOV that it gets dirty, cleaning it helps.

BTW, cutting a spring *raises* it's spring rate. If you're shortening it, that's a winning battle, but cutting it and adding washers makes it stiffer.

Sometimes I worry about mine opening under boost though. :-) I've got it pretty light and I really have few issues with it - if I want it to blow off I lift quick, and if I don't I lift slow.

How are you going to install it in place of urs?

LInk me to the auction, I may want to get one as well.

AbeFM:

Correct, cutting the spring does make it stiffer but in my case for some reason it works better. Maybe because its stiffer, it resists the surging better? If the spring is softer, it could possibly intensify the surge acting like a rubberband? Although a softer spring would probably open easier under vaccum from the manifold behind the throttle body and boost pressure inside the intercooler piping. It does open ever so slightly at idle, but it makes a whole lot less turkey gobble (flutter) and can hear a soft wooshing noise now. Still sucks though cause the flutter is still there. I want to get rid of it completely. It may sound pretty cool, but in the end I know it is detrimental to my turbo.

Well, this BOV is brand new and isn't dirty at all. Maybe I just have to somehow break it in and wear the spring down allowing it to sag.



Sam:

this is the one I am going to purchase:

http://cgi.ebay.com/ebaymotors/Turbo...spagenameZWDVW

This one is a cast one:

http://cgi.ebay.com/ebaymotors/Bov-B...spagenameZWDVW

Noticed that there are a couple different types of type S BOV's some are cast with CNC'd parts, others are completely CNC'd. I opted to purchase the completely CNC'd. You can also find them with mild steel bungs, SS bungs, or just full pipes with the bung welded on. Right now I have the Turbo XS weld on bung welded to the intercooler pipe. The Ebay Type S weld on bung appears to be a little larger than the turbo xs one so I'll just cut it out and weld the new one on. Simple. Hope this shit works.

I see the second one has a weld on bung like the turbo xs, but I Just dont see how the greddy bov is supposed to mate to it if it uses its own proprietary flange.

I was thinking of getting another valve but without having to remove my welded in bung, just throw a coupler on it with some tbolt clamps.

I was looking for a BOV with the largest opening possible. The Greddy Type S looks big enough at about 34mm.

1> The TurboXS RFL is notorious for flutter, because it does not have the attached vacuum line that the S does to pull it shut. Its a hell of a BOV for sound, but for functionality, use something with that vacuum port like the S has.

2> I have experience with both the ebay S and the real S BOVs. I did not run the ebay S long enough to really test whether or not it was the cause of my vacuum issues, but I can say that I am far more impressed with the real S BOV as far as vacuum and sound.

hey supersuk, heres a question for you.

How many shims are you using in your TurboXS? I went from four to two, and its cracked 1mm at idle. Flutters for half a second in low rpms.

Either way, let me know how that knockoff works for you. If it works well then I will pick one up also.

When you guys are describing flutter are you talking about compressor surge (gobble gobble)?

I think it's time for a sounds clip.

just buy a real bov :p,,

both me a friend had flutter, and we both switched to real bov's

i got the turbo smart series 2, and he got that stupid hks one

but they work great. i vta with a afm still in place with no stalling issues, no hiccups, and no flutter or surge

I'm 99% sure they are talking about flutter.. aka.. blow off.. then flutter as the valve attempts to close. Pretty common on the XS

+1. I'm still not sure what they are talking about, though I think it's it.


Also, in the 80's, 90's, I had lots of friends with no BOV at all, tons of surge (gobble) on every shift, and there was no broken turbos that I saw.

If it's at idle, here's what you do to fix it: Turn up your stereo. Seriously, it's not like you're slamming a high speed turbo to a sudden stop.

If it's happening as you flick-shift from 3rd to fourth at 18 psi and full revs, then you should do something about it.

And if it's open at idle, see if air is coming out. Otherwise, it's sucking in. And your blinging K&N "filtercharger" is doing nothing while you suck in road debris through your BOV. :-)

flutter and blow off are different things.

Let's try "Surge" (i.e. the gobble gobble sound of the turbo stalling, dumping pressure OUT the air filter) and "vent" where air comes *out* of the port in the side of the blow off valve.

And this is why I want a sound clip :)

I know exactly what surge is..and I was defining the sound in sequence. The flutter generally occurs after the initial "vent out of the port of the side of the blow off valve". I would strongly disagree with surge if the damn thing is leaking at idle.

I was looking for a sound to demonstrate, but i found this and though I would show. Before Abe jumps on my case as me calling this flutter.. I'm not... Here the fluttering is occurring before the actual purge. Plus the term they use is just funny.

I have the TurboXS and it doesnt flutter the way you describe, it surges for half a second at low rpm but thats it.

Awesome, not only is that a good find, it also warms my heart to see a WRX all dolled up, pulling boost then failing to gain on a raised SUV. :-P

I imagine that place has some tips on curing the problem. Perhaps moving it closer to the throttle body helps. As I said, a quick lift always helps me. Bigger line to the BOV might be good, but yeah, some BOV's are just crap, too.

(Not trying to get on anyone's case, somehow I read that earlier statement to mean those were the same thing)

Mines is the BOV flutter, it sounds exactly like how the wrx bov does but without the dump at the end, well most of the time. Well, the flutter on mines is a lot faster and lasts for about 2 seconds. I'm sure because of the flutter there are pressure waves still going to the compressor trying to stall it, but not as bad.

I'm gonna try that ebay Type S as a lot of my friends have had success with these. If that doesn't work, all i'm out is only $36 so no big deal. I can prolly just sell this one and get either the real thing or some other BOV that fits.

Oh, and I know how real bad compressor surge sounds like. My friends ghetto turbocharged 240 has no BOV and he likes to boost it to 15psi. That thing sounds like you're trying to kill a turkey, I crack up all the time I hear it. He thinks its cool so just keeps it that way.

Yeah - I wonder if the vacuum signal is getting to your BOV? It's supposed to actively open when manifold vacuum pulls on it.

In my mind to get rid of the flutter, a softer spring should be employed? I get this flutter at low RPM occasionally.

If that were the case he'd get gobble gobble.

At first, I had no washers in my BOV. When I put washers in, it wouldn't even open at all until I hit like 7-8 psi. Once I cut the spring it started to open at around 4 psi. Then I cut the spring again and started to open at around 2 psi, but started to leak at idle. It was sucking in air. So in order to fix that I put in 2 washers. Now it blows off better and doesn't leak at idle, although the flutter is still present. Its more so during high boost runs of 8+ psi. I also noticed that when I lift off quick it does the flutter more so than when I lift off slow. If I lift off slow then it does a nice but soft dump with no flutter.

I wanted to try that at first, but didn't know where about to get a softer spring. I wouldn't mind trying a softer spring. I guess I should try looking for one. Anyone got any suggestions?

Something is weird there... Lifting fast just means you actually have more air that NEEDS blowing off, and I think that's exposing your problem. My guess is either the hole is too small (but unlikely, since there's no much air at idle).

Having the spring not even touching, which sounds like what you're doing, will help it open easier, but open less under real pressure. This probably hurts the function of the BOV when it actually matters, but not so much in traffic.

That's the distinction I think. While lots of very hard surge is bad for the turbo, the truth is, a little bit won't hurt it. The real purpose of a BOV is to keep you from having to spool up the turbo again after a shift. It's not for longevity, though it helps there, it's a performance mod.

My buddie's dodge I was talking about, he had to respool after every shift. That meant a second or more of off-boost after every shift, slowing things down alot. After a hard shift in my miata, I'm at full boost in a fraction of a second. MUCH BETTER, and all thanks to the BOV.

For that, you want it to open far, and wide, but not to open too early (idle, etc). So a weak spring with some preload, even if it makes it surge in stop and go, is probably the way to go, if you have to pick.

The spring in my bov is about twice as long as the bov itself even after I cut coils off. The washers in the bov help to effectively increase amount of vaccum needed to open it during idle.

Think of the turbo XS BOV as a cylinder with a piston in the middle. One side is hooked up to the intercooler pipes while the other side hooked up to the intake manifold with a spring on that side. When the engine revs up and builds boost and you let off the throttle, the pressure differential between either side of the throttle plate should be what opens the BOV. The vacuum from the intake manifold pulls the piston while the boost pressure inside the intercooler pipes push the piston open. While under boost, the pressure from the intake manifold and the spring push on the piston while the pressure from the intercooler pipes also push on the piston. I think that the reason the BOV flutters is because the spring in the BOV is not matched to your system. Its like a shock that doesn't damp enough and has to much rebound.

The only way I think to make this thing work better would prolly be a softer spring or maybe a shorter spring with the same spring rate. Instead of wanting to trial and error, i opted the easy way out and just bought a new one. Ha Ha

You're fucked. Flutter is a part of life with most BOVs. Just WOT all the time and get nice poowshes and be happier or like the purr like a kitty noise your badass turbo miata makes. Chicks will like your car even more. The end. The video had a synapse BOV. It was an add for their BOV. It's sphecial.

My car doesn't surge, almost never. It's the 'old style' FM BOV.

BTW, if you've got hardly any spring in there, what happens when you do this:

Light boost, or easing off the throttle. Pressure in the manifold, say, 4 psi. In the IC piping, 14 psi, across the throttle plates there's a drop of 10 psi. Your BOV will open.

Now your turbo is pissing air out of the lines. Doesn't that tick you off? (Ok, I don't think it really matters)

If you can make that condition happen, which is highly unlikely. At light throttle, your car will not make that much boost anyways unless you have a tiny little turbo. I don't think you can have that kind of pressure differential on either side of the throttle body unless you make the throttle body pretty small and it just opens up into a huge manifold (like enormous!!). Only vacuum and boost. It also won't matter if you're easing off the throttle. Am I making any sense?

If your BOV flutters then you've got issues. It shouldn't flutter when properly working.

i use to get flutter at partial throttle around 0-5psi...its annoying

Yeah, It gets on my nerves cause I feel like I'm doin damage. Don't know if I am or not though. Seems like the BOV works a little better now. Not getting as much flutter, but its still there. So Greddy knockoff here we come. I'll post an update once I get this done, maybe in the next couple weeks. Car is in the process of getting many things done.

I had the HKS SSQV for a couple years and always ran it with the line hooked up. Somehow one day the vac line came off and I had the gobble. I figured out what it was and fixed it, but I pulled it a couple times after that to show some friends.

I've heard both sides. Some say its super horrible for turbos. Other guys have said they never heard of any problems with surge before. Alot of videos I see from Japan demonstrate the no BOV surge. I've never heard the late BOV flutter like that before.....that definitely sounds off. :td: Either way I prefer to run a BOV.

Vash-

Again, the biggest reason to run a BOV is so you don't have to respool after a shift. When you stop the compressor,you have to spin it up to get boost.

I could swear mine's blowin in the recirc port all the time - it's slow to spool sometimes, and noisey, othertimes it's fine.