http://media.putfile.com/bov90

About 4 seconds into the clip you will hear a "foom" sound while the BOV releases air. I drove the car around and noticed that when I shift at 2500rpm I will hear the "foom" sound. Boost is ok and the car pulls the way it should. Any ideas. I am running a stock SC kit with stock pulley.

 

Sounds like alittle bit of the air is not being released out of the BOV and is going back through the Blower unit. If you cover the outlet of your BOV and rev your engine a tad bit, youll hear the sounds im explaining...its kinda like a surge woohhhhh..almost like a deep howel

Its looks like its functioning correctly, and opening the correct amount.

-matt

 

My car makes the same exact noise, but i think it's a little more obvious on mine.
I do have the older Blitz BOV though. It gets kinda annoying on the freeway when cruising around 2-3k rpm.

 

I thought long and hard about this, and eventually came up with an explanation. With turbos you hit max psi boost as soon as the turbo spools up, but with the SCer, you only see max boost at the top of the RPM range (6k, lets say). So, anytime you're shifting in the low RPM range, say less than 4k, the blower is only blowing at maybe 3 or 4psi, not enough air pressure to push the BOV open, but enough air to go out the other direction.

I know the BOV is vacumn operated, but there still needs to be enough air pressure to push the spring/diaphram up to let the air out. This would certainly explain why I get the "foom" sound anytime I shift below 3500. If I shift at 4k or above, it blows off perfectly.

 

The same happens with me. I notice if I shift above 3500 I don't hear the "foom" sound as much or not even at all. Is this just the case with the Blitz DD?

 

I have a Blitz SS (old school horn design).

 

I got that old school bov aswell. It is just the air going back through the blower like you said. You can always loosen it up enough to where it won't do that as bad. All up to you.

 

This is normal with a supercharger... we are making boost with pretty much any rpm (amount obviously varies with rpm) so when you release the gas (vacuum) there will be some boost leaked out. In fact, I have my Blitz DD set so it bleeds this boost at idle. Turbos requires some "gas" to spool up and make boost. This is the exact reason I would not put one of those "tweety bird" BOV cuz it would be annoying as heck on our vortech kits.

BTW you obviously have a V1..... LOL.

 

Looks like he has a V2 plate

 

Didn't notice with all those angry crickets...

 

I replaced the spring in mine to reduce the pressure a little bit so the BOV will open quicker and not produce compressor surge as easily. Mine is quiet all the time and I don't get any boost leak, but I'm only running 6psi too.

 

Yup, I have a V2 plate.

 

Okay a little update on this.

The problem was that the spring inside the BOV is far too stiff for our cars running lower levels of boost. Between 2000-3500rpm, we're only making maybe 2 or 3 psi at most, which isn't enough pressure to push open the blow off valve, which means the air has to go back out the opposite way it came back through the blower. The stock Blitz spring is for cars running 12-16 psi of boost (made for turbos). They do make a replacement spring, but it's even stiffer for cars running 16+ psi.

After searching far and wide for a softer replacement spring, I finally just bought a generic spring from the local hardware store that was softer than the stock Blitz spring. This afternoon, I opened up the BOV, replaced the spring, went for a drive and...

NO MORE "foom" COMPRESSOR SURGE! Yup, none. I might have to play around with the preload adjustment screw a little more because I'm only getting 7psi max boost now (I was getting 8 before), but atleast it doesn't make that god awful "foom" noise anymore. Now I can shift at any RPM I want

 

hmm - from listening to the clip it sounds like compressor surge - i wonder if you are making enough boost to kick open the bov -

 

Wow...Deja Vu.

http://69.57.150.24/showthread.php?t...V+spring+surge

 

I was thinking of switching BOVs, now i wouldnt even know what to get. i was looking to go the ssqv route and get rid of the blitz dd....i have an automatic so im not releasing air at low rpms unless i let off the gas early. so compressor surge or "foom" is not as constant a problem on my car, as opposed to you 5spd guys. with that said, should i switch to ssqv? or stick wit blitz, and possibly modify spring for blitz? (not a big fan of losing a full psi of boost though) thanks, dont mean to hijack either....

 

I would NOT use the SSQV because of what I was saying.
The SSQV in no way allows the release of air when not coming off boost.

WHich means when cruising on the freeway at 3000 RPM for example (like in the auto) - you will be surging your compressor pretty bad.

 

Thanks ian...so the Blitz gets the best review, functionality-wise i take it. Aside from the mondo BOV guys are using. the leaky greddy type s, and tight ssqv are out the window i guess...

 

Any reviews on the new greddy RS?

 

Yeah - I LOVE the look and sound of the SSQV - but functionally speaking it doesn't do the job.

 

Tell me about it

Have you heard of the greddy RS? The blitz just sounds so bland and generic to me.

 

What BOV really does the job good then ??

Lets no air at idle, and opens up and lets enough air out after boost. I have hearing surge every time i shift...really annoying

Everything I read about the SSQV, it explains the double action diaphram. sounds really promising but you say its bad


-matt

 

when I let off of the gas at cruising speeds w/ my SSQV the pressure vents. I can make my car surge pretty hard when cruising in first gear between 2.5-3 grand. The car is not boosting in either sitiuation.

 

I really want the SSQV, lol, tell me its functionality is better than ian and i thought please, lol.

 

For Turbo the SSQV is great since it will never release any air at idle. However for a Centrifugal SC this is terrible since it is always pushing a significant amount of air while a turbo is barely spinning at idle and cruising loads.