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Old 10-06-2001, 12:58 AM   #1
astrocreep
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Default What does a blow-off valve

I guess the title is pretty self-explaining. Any info would help. All i know is that it is apart of the intake manifold i guess?
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Old 10-06-2001, 03:24 AM   #2
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A blow-off valve vents excess pressure from the intake tract to prevent it from damaging the turbo. The surge of air associated with the throttle snapping shut when you shift would normally force a lot of air back onto the compressor blades.


Ben

Last edited by bsquare; 10-06-2001 at 06:22 AM.
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Old 10-06-2001, 03:42 AM   #3
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amen to that brother
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Old 10-06-2001, 04:57 AM   #4
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perfect explanation
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Old 10-06-2001, 01:19 PM   #5
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Hey it all makes sense now, the meaning of life, why they give you 8 hot dog buns when hot dogs are sold in packs of 10. Seriously though thanks for the info much thanks
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Old 10-07-2001, 03:31 AM   #6
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The best explanation of wastegates and blow off valves Iíve seen in print has to be in the July 2001 SCC issue as a part of the Suck, Squish, Bang, Blow articles. Grab a copy of that if you can, it explains wastegates too
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Old 10-07-2001, 04:15 PM   #7
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what's the downside to blowoff valves??? i heard they can also do the opposite and hurt your turbo. whats the chance of that happening
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Old 10-07-2001, 04:28 PM   #8
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Quote:
Originally posted by Penguinking
what's the downside to blowoff valves??? i heard they can also do the opposite and hurt your turbo. whats the chance of that happening
They can only hurt your turbo if they dont work. Like if they are stuck or you have the wrong spring in the valve. A really stiff spring will let more pressure build before the valve pops open.
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Old 10-07-2001, 08:25 PM   #9
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Is blow off valve the same as a by pass valve? What's the difference?
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Old 10-07-2001, 10:20 PM   #10
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subies-

theoretically yes but work in different ways depending upon the system.

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Old 10-07-2001, 10:35 PM   #11
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A blow-off valve is not capable of damaging your turbo unless it fails at the wrong time (meaning when it is needed and you are running a ton of boost). There can be problems with atmospheric venting BOVs and certain air flow sensors which get confused by the sudden change in pressure, but this doesn't really hurt anything. Recirculating valves (which pump the air back into the intake tract on the other side of the turbo) will not cause this problem. Also, recirculating valves make a lot less noise (a very good thing since I find loud BOVs really annoying).

I'm not sure what you mean by a bypass valve, but if it is a pop off valve, the idea is to act as a backup for a wastegate which is not working correctly. If the wastegate fails to open or can't vent enough exhaust, the turbos will make excess boost (called creeping or spiking). A pop off valve is generally a purely mechanical device (meaning no solenoid), which vents excess pressure in the intake tract. So, while a BOC only vents when there is the surge associated with the throttle closing, the POV will vent, no matter what, once the pressure hits a certain level. For example, if you are running 10 psi and your engine will die a horrible death if you get to 14psi, you could run a POV with a spring set to 27psi (14.7psi atmospheric + 12.3psi of boost) to vent if the boost ever crept or spiked over 12.3psi.


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Old 10-08-2001, 12:34 AM   #12
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bypass valves are used in factory supercharged setup...perform the same function just designed in little bit of a different way.

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Old 10-08-2001, 07:05 PM   #13
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I've heard the term "bypass valve" used synonymously with "blow off valve", especially in systems where the valve in question is plumbed back to the intake (i.e., not vented to atmosphere). I think either is acceptable in polite conversation, though one or the other might be more strictly correct.
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Old 01-16-2006, 11:42 PM   #14
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Old 01-18-2006, 05:38 PM   #15
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??

Peaty man, with all the BOV threads, why did you bump a 4.5 y/o thread?
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Old 01-18-2006, 05:48 PM   #16
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At least I posted some info and not another question
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