Car geeks, help me out.

  • We are currently upgrading MFK. thanks! -neo
Pop off valves are a safety feature rather than a preformance inhancement and they only work on turbochargers or centrifical type superchargers. (for the most part...on turbos they reduce boost on deceleration.) A roots blower is bolted directly to the manifold with no real effective way to reduce pressure.

Superchargers are designed to provide boost at all times and at all engine speeds so I fail to see how releasing that manifold pressure in "OH WOW MR' cool dude" bursts has any sort of preformance increase.

When we use 8 and 10-71 blowers on large displacement big blocks we install a small pressure relief valve to bleed off manifold pressure when the engines shut down but like i said this is a safety feature to prevent a possible explosion.
 
Wolf3101;1199738; said:
Pop off valves are a safety feature rather than a preformance inhancement and they only work on turbochargers or centrifical type superchargers. (for the most part...on turbos they reduce boost on deceleration.) A roots blower is bolted directly to the manifold with no real effective way to reduce pressure.

Superchargers are designed to provide boost at all times and at all engine speeds so I fail to see how releasing that manifold pressure in "OH WOW MR' cool dude" bursts has any sort of preformance increase.

When we use 8 and 10-71 blowers on large displacement big blocks we install a small pressure relief valve to bleed off manifold pressure when the engines shut down but like i said this is a safety feature to prevent a possible explosion.
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The car has a boost bleed valve solely for the purpose of keeping the engine from being under too much pressure. Originally, they didn't test the engine beyond 12 psi and programmed the computer to let off anything above 12. Since then they have tested it up to 17, and newer models will not bleed boost. I bypassed the boost bleed off on my car.

Secondly, I thought blow off valves were meant to prevent back pressure on a turbo to keep it spooled, thus preventing boost loss on shifts. What floors me is where in the hell would you put a blowoff valve on an engine with a roots type supercharger, even if you only wanted the noise? This guy is advertising it for the Cobalt SS and Ion Redline, which have Rots SC, and the Saab 9-3 which is turbo. I think he screwed up thinking all LSJ engines were supercharged.
 
ewurm;1199758; said:
Secondly, I thought blow off valves were meant to prevent back pressure on a turbo to keep it spooled, thus preventing boost loss on shifts. What floors me is where in the hell would you put a blowoff valve on an engine with a roots type supercharger, even if you only wanted the noise? This guy is advertising it for the Cobalt SS and Ion Redline, which have Rots SC, and the Saab 9-3 which is turbo. I think he screwed up thinking all LSJ engines were supercharged.
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You're partially right.. that is one of the reasons for a BOV, but the other more important IMO is for somewhere for the air to go when the throttle plate closes and so it doesn't send the air back into the turbo in the other direction..

Here's a photo I found of what I assume is the supercharger on your car.. If your bypass valve is that little black valve it looks like it's built right into the supercharger housing. So short of finding a special peice made to switch in for the old one I don't think there is an upgrade you can do with a generic peice. I don't have an answer on how to adjust it to not bleed til over 17lbs, but if I see something I'll let you know.

9c71_1.jpg
 
cichlaguapote;1200270; said:
You're partially right.. that is one of the reasons for a BOV, but the other more important IMO is for somewhere for the air to go when the throttle plate closes and so it doesn't send the air back into the turbo in the other direction..

Here's a photo I found of what I assume is the supercharger on your car.. If your bypass valve is that little black valve it looks like it's built right into the supercharger housing. So short of finding a special peice made to switch in for the old one I don't think there is an upgrade you can do with a generic peice. I don't have an answer on how to adjust it to not bleed til over 17lbs, but if I see something I'll let you know.
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yeah i was gonna mention this, but you beat me to it, but not as an opinion rather a neccistity IME.
 
My whole point was that a Blowoff Valve will not work on a roots style Supercharger. It would work on a centrifugal SC, but he is selling this item for MY car. I pointed this out. He gave me a link to the wikipedia listing for blowoff valves, which says what I just said.
 
ewurm;1202205; said:
My whole point was that a Blowoff Valve will not work on a roots style Supercharger. It would work on a centrifugal SC, but he is selling this item for MY car. I pointed this out. He gave me a link to the wikipedia listing for blowoff valves, which says what I just said.
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Sorry Wurm.. Didn't know your intent, but thought after re-reading it that it was your intent just to verify he's wrong not for interest in it. And yeah you're right he's wrong and just trying to get exposure to make a buck.
 
yea BOV on a roots type blower just won't work the way they're intended to work.

You don't need to worry about keeping your blower spooled because it's belt driven.
 
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