BOV flutter/(surge?) under high boost, perfect at low boost...

[EricGRIT09]

Hey everyone, I've been working on tuning my car and things have been getting better and better. Thanks to everyone on this site for that.

One problem I'm having now (even after searching and trying to figure this out on my own) is that my BOV is releasing pressure beautifully at 0-5 psi, but any time I boost over 10PSI I get what sounds like compressor surge. This doesn't make sense to me because if it is releasing at low boost levels, it should actually release even better at higher boost levels right? My current boost is 18psi, and it will flutter/surge if I let off the throttle quickly. If I close the throttle plate slowly at 18psi, it will blow off better. I have adjusted the adjustment screw both ways (greddy rs), and it seems to only affect the lower boost levels, but always flutters/surges at high boost levels.

P.S. I understand the difference between a bov flutter and compressor surge, and I'm hoping its just a flutter because it definitely opens at low boost levels. To me, though, it seems weird because my bov has always blown off fine at higher levels, but I have been adjusting many things, though not directly related to the BOV. My vacuum is at -22 at idle, and is fine when I let off the throttle also.

Thanks again!

[GVR4592]

Where do you have the vacuum line connected?

[EricGRIT09]

straight to the throttle body... brand new hose, but same location as the stock line

[GVR4592]

Try moving it to the intake manifold.

[Eastwood95]

You probably already have it hooked up to the intake manifold if you reused the stock line location. I would keep trying the adjustment screw, although it sounds like your getting a push/pull reaction. Do you have your BOV tee'd into your MBC?

[EricGRIT09]

nope, direct line to the throttle body, shortest route possible... no kinks, and holds vacuum just fine...

very strange :/

[blazebolt]

I had the same problem on my RS until I did the single spring mod. Took out that spring and no more compressor surge.

http://www.evomoto.com/tech_info.php?tPath=1&tech_id=7

[Clay]

Also check for vacuum in the line going to the bov. The previous owner of my GST used a plastic vacuum T which broke apart and blocked the "port" inside the intake manifold. I verified the blockage by attempting to push air into the "port" with an air compressor. Solved my problem by dislodging the plastic fitting with a metal coat hanger.

Apologize to 'eclipsetech' for using/modifying his engine photo. The red highlight is the line I'm talking about. Sorry for the confusion with the term "port".

[GVR4592]

I don't know about 2g's but on 1g's there's only port on the throttle body that has vacuum. Just switch it to the intake manifold to eliminate the possibility that the vacuum source is the issue, then we can move onto other things.

[Turboeagletalon]

no u should be useing the stock port on the intake manifold directly behind number three injector

[EricGRIT09]

yeah thats the thing, the vacuum is fine in the tube (as far as my finger can tell), and its weird that it blows off at low, but seems to have trouble at high boost.... i dunno maybe the diaphragm is messed up somehow?

[blazebolt]

Try the single spring mod. I'm almost positive that is your issue. It is a requirement on EVO's with RS BOV's and it worked for me on my 95GSX and others as well.

[Turboeagletalon]

it makes sense you would think that is would make the valve more responcive, but does mhaveing ut make it's abuility to holp boost delinish, but being a spring short

[blazebolt]

^^ Spell check and grammar please.

From what I understood from what you are saying, you are correct that it would make the BOV more responsive. You will have trouble holding higher boost with just one spring in there, so you should do a boost leak test after you perform this mod. I do not know how much boost the one spring can hold. I'm currently boosting 18psi with no leaks and no surge.

[daren_p]

When I ran the Greddy Type RS it did the same thing the way it came adjusted from the factory. It was flutter & not surge though, if its surge you should be able to tell as its alot more violent & the car will sorta buck. What I did to get the valve to blow off correctly is basically adjust the springs to have the least amount of tension. Just back the adjuster bolt out until you fell no spring tension on it, then just screw it back in till it just touches the springs. This may work for you, if not you may have to remove the smaller weaker spring, like was said. While you at it make sure you have sealent on the pressure port fitting & on the adjusting bolt.

It sounds like you've got a direct line, so make sure its to the intake mani & that the vacuum is of a good/proper size.

[EricGRIT09]

Yeah i'm assuming its flutter also, because it shifts just fine and no bucking at all at the higher boost levels. Nothing i would ever consider remotely violent I'll try adjusting it to the weakest level, and if that doesn't work i will take out the spring once i get back to my garage.

Thanks guys! (btw... properly tuned 18-20psi feels nice... im liking this daily driver )

[johnfsmith]

I've had the same problem and tried adjusting it and never could get working. I saw this thread and removed the smaller spring and it's finally working. Thanks!