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Location:
Sydney
Registered:
July 2002
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Centrifugal supercharger BOV
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Wed, 09 April 2003 01:09
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OK, I know the principals behind putting a BOV on a turbo car as there is still boost going in when the throttle closes and ends up slamming against the closed throttle butterfly and with repeated use can damage it.
With a positive displacement supercharger (roots type, or one from a 4AGZE/1GGZE) there isn't as much of a need as there is no more boost because the amount of boost is directly proportional to revs.
What about a centrifugal supercharger? They have a design similar to a turbo, so I'm not sure if it would boost when the throttle is closed, as it would be run on bearings, not directly on the crank speed.
My question is:
Would an engine with a centrifugal supercharger benefit from having a BOV??
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Location:
Brisbane
Registered:
May 2002
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Re: Centrifugal supercharger BOV
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Wed, 09 April 2003 01:14
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Uh, all superchargers (including centrifugal types) are run directly from the crank, and they all "run on bearings" as well.
I have heard of people running BOV's in blow-through centrifugal setups, but I'm not sure if this is beneficial or if it's just for the rice factor.
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Location:
Sydney
Registered:
July 2002
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Re: Centrifugal supercharger BOV
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Wed, 09 April 2003 01:24
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Positive (or is it negative?) displacement superchargers fully enclose the air and force through x amount each revolution. Centrifugal ones have to spool up like a turbo to produce boost.
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I supported Toymods
Location:
Perth
Registered:
May 2002
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Location:
Sydney
Registered:
July 2002
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Re: Centrifugal supercharger BOV
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Wed, 09 April 2003 02:43
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Thats what I was thinking.
I've got a really nice HKS BOV that I pulled off my 7M, if I can fit a centrifugal supercharger in with the 1U I'll put the BOV back on.
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Location:
Brisbane
Registered:
May 2002
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Re: Centrifugal supercharger BOV
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Wed, 09 April 2003 08:34
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A centrifugal supercharger does not spool up anything like a turbo; the revs of the compressor are directly proportional to the engine revs. Yes they develop boost as an exponential function of rpm, but that's not the same as saying they "spool up".
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Centrifugal supercharger BOV
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Wed, 09 April 2003 11:39
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This is simple stuff! With any kind of mechanically driven blower, whether you need a BOV(damn I hate that term!) depends on whether the blower is mounted before or after the throttle. If the throttle comes first, there's no way in hell you can use one - obvious and simple. I've seen wallies try and put them on 4AGZEs and wonder why the hell they don't work.
BUT if the blower comes BEFORE the throttle, you MUST have something, ESPECIALLY if it's a positive displacement type - this is because after the throttle shuts, the engine is still driving the blower, and it will build up enormous pressure in the inlet pipework, if you're lucky blowing off a hose or less lucky bending the throttle (with the appropriate results!)
Simple - a throttle before the blower (such as 4AGZE) cuts off the air, therefore there's no air to vent (otherwise the engine would still be going hard!).
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