Wankel7

For some reason when gently accelerating (breaking in a new engine) the BOV makes this weird fluttering noise...I have no idea how to describe it...but it happens when you are just gently accelerating thru the gears. When you let off the gas to shift.

I have it hooked up to a vacuum source but I dont get it.

It is a HKS SSBOV.

James

1987RX7guy

iTrader: (3)

hmm that's wierd i'd like to know too

RotaryEvolution

iTrader: (30)

what kind of mods do you have?

with a BNR and big front mount i'm pretty sure it is normal.

just because there is no positive manifold pressure doesn't mean the compressor isn't producing boost.

turbo-polak

ive been trying to figure out what the sound is for a while now... i personally love it.. .hah

a couple people say its the wastegate flapping, and other people say its the BOV, and others say its the boost pushing back on the turbo, trying to spin it backwards...

RX_AV8TR

I can only think that you're talking about the compressor surge sound when the BOV does not open, I'm betting that you don't hear the fluttering when you hear the hisss of the BOV opening up.

That's normal, you can reduce the tension on the BOV to reduce the flutter, well, in case that's what you're hearing, I think that's what it is.

RotaryEvolution

iTrader: (30)

it is a compressor surge, a very slight one as the BOV vents very slightly after mild boosting.

(shouldn't hurt anything, mine does this also)

CyborgRyu

iTrader: (8)

https://www.rx7club.com/single-turbo-rx-7s-23/how-fix-compressor-surge-444838/

I'm having the same problem. I fixed my vaccuum lines and such, I can only hear my BOV after hard boosting.


I tried taking the BOV apart, but how do you get the spring/washer out? Is there a trick?

RotaryEvolution

iTrader: (30)

the SSQV does not like the stock top mount intercooler, it will suge under light boosting until you free up the intercooler flow.

CyborgRyu

iTrader: (8)

https://www.rx7club.com/showthread.php?t=435084

Karack, here are my mods. Do you know why I can't hold boost or why it flutters?

RotaryEvolution

iTrader: (30)

the wastegate actuator return spring is probably too loose, the BNR turbo should have an adjustable wastegate actuator rod on it so you can manually tighten it, try shortening the rod length and see if it helps.

that or you have a leak in one of the IC pipes/hoses or a vacuum leak somewhere which is losing boost under pressure.

Wankel7

You guys are right on the compressor surge.

If you rev it from idle with your hand over the TID you can feel air being blown back out of the TID when it decels. However, the BOV valve does blow air out.

So, what does that adjustment screw do on the HKS SSBOV?

I would love to fix it because it is rather annoying.

James

Wankel7

Oh , I have the Greddy V spec FMIC....and my BOV is about one foot downstream of the turbo.

James

MARTIN

Exactly...

CyborgRyu

iTrader: (8)

Did you fix the flutter??

Any other guys with a BNR turbo experianced this problem before?

Ever since I redid my vaccuum lines, I can only hit 8psi, but now I don't drop at all. Its a some what plus...

Wankel7

Huh, my problem and your problem are two entirly different things.

My issue has nothing to do with the wastegate....

Seems like yours does.

James

ilike2eatricers

I have the same problem as you wankel7. Greddy fmic, hybrid, and greddy type S about 1-2 feet from the turbo. Under very little boost it would surge. I adjusted the spring on the bov to get rid of the surge but now have the problem with the bov opening slightly under no boost making a sqeak sound and also when getting off throttle the bov stays open much longer. Any tighter and I get compressor surge (fluttering sound). I'd rather run slightly richer inbetween shifts than getting surge. I've never had the problem until I put on the fmic, I think it's because so much more volume of air is left in the pipes making it difficult for the bov to vent all of it after low boost levels while at high boost levels causing it to stick open longer since it's forced to open wider. Not sure if that makes sense but it does to me.

Wankel7

Maybe putting the BOV after the intercooler would calm this problem down?

James

ilike2eatricers

Possibly I've seen BOVs mounted on either side of intercooler pipes. I think there was a thread with a debate about location, maybe I can find it.

NZConvertible

Just to be clear, the BOV isn't making the fluttering noise, the turbo is. The BOV is not relieving enough pressure to prevent air being pushed backwards though the compressor, and this air makes a fluttering sound due to the spinning compressor blades. Since you're breaking in the engine I assume you're keeping the revs down. Because of that there isn't enough manifold vacuum being generated to open the BOV sufficiently to prevent a bit of surge. You should adjust the amount of vac needed to open the BOV so that it's just closed at idle, but opens at vac lower than that. Personally I wouldn't get too worried about it unless it does it at higher revs and loads.

RotaryEvolution

iTrader: (30)

are you 100% sure about that NZ?

it sounds like the BOV is opening a hair to me but not enough to relieve enough pressure causing the surge.

the SSQV is not adjustable to open at different vacuum levels so that is out of the question.

i wouldn't be worried about it either, i don't worry about the compressor surge much unless it happens when the turbo is really being pushed.

1987RX7guy

iTrader: (3)

I was with wankel7 when we "confirmed" it was compressor surge. I did happen to mention that wanke7's original "vac" source was the wrong kind of nipple and we switched it to another one, after that I put my hand on the face of the BOV(where it would discharge air when it actuates) and I grabbed the throttle and rev'd from the engine bay, no BOV actuation. I asked wankel7 to do the same while I reved from the cabin, same result.....wankel7 then removed his filter and we tried it again, air was forced out of the TID. It IS compressor surge. No air or noise is discharged from the BOV that is even similar to the flutter(gobble gobble) noise. I agree with NZ that the BOV needs to be made more sensative so that it opens even below 0 PSI.

Santiago

RotaryEvolution

iTrader: (30)

then it would be open at idle when there is manifold vacuum present, you mean it should be more sensitive to anything over 20in/hg.

ilike2eatricers

Sooo somewhat on topic...

Has anybody flowtested all the vac sources to see which one pulls/pushes the most air? Where is everybody sourcing their vacuum from for the BOVs?

I'm using the top nipple on the front of the UIM, straight line with no tee offs. Havent really tried any other ones yet since I'm lazy.

RotaryEvolution

iTrader: (30)

i sourced it from the stock location, figured the factory knew best. the BOV actuation is still based on the same principle as the stock one.

ilike2eatricers

Do you have an FMIC karack? I think with the stock TMIC location wouldnt matter much. I figure the main problem is all the extra volume in air compressed into the pipes for the FMIC while the TMIC has a very short route.