Weird sound from Blitz DD BOV. (Clip inside)
10-16-2005, 09:03 PM
#1
Weird sound from Blitz DD BOV. (Clip inside)
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.
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.
10-16-2005, 09:26 PM
#2
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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
Its looks like its functioning correctly, and opening the correct amount.
-matt
10-17-2005, 12:06 AM
#4
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.
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.
10-17-2005, 12:24 AM
#5
Originally Posted by ewuzh
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.
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.
10-17-2005, 01:04 AM
#6
Originally Posted by blarg
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?
10-17-2005, 05:23 PM
#8
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.
BTW you obviously have a V1..... LOL.
10-18-2005, 07:13 AM
#11
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.
12-28-2005, 01:17 AM
#13
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 
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
01-07-2006, 10:29 PM
#15
01-17-2006, 11:09 AM
#16
Senior Member
Join Date: May 2005
Posts: 158
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....
01-17-2006, 02:44 PM
#17
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.
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.
01-18-2006, 10:06 AM
#18
Senior Member
Join Date: May 2005
Posts: 158
Originally Posted by iansw
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.
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...
01-18-2006, 10:39 AM
#22
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Location: Northern Jersey
Posts: 10,166
Originally Posted by iansw
Yeah - I LOVE the look and sound of the SSQV - but functionally speaking it doesn't do the job.
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
01-18-2006, 11:02 AM
#23
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.
01-18-2006, 01:23 PM
#25
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.
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