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Blow off valve work on supercharger?


premo-s12

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so im doing a custom install w/an eaton M90 on my 87' SE 200sx/s12 (vg30e) . i have the complete unit sitting, i have all my adapter plates, brackets, etc, etc made, but i have one last thing to do...thats the bypass valve. now its gonna be a complete pain in the ass to plumb and i was wondering if its kosher to run a BOV on a blower? sorry, this might be a dumb question, but im a turbo guy and blowers are fairly new to me. anyhow, i have a BOV sitting on the shelf and this would WAY simplifiy my install. would it just be constantly making a 'blowing off' sound as the engine would be turning the blower? could i just put the TB after the blower? any info would be greatly appreciated!! thanks in advance

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so im doing a custom install w/an eaton M90 on my 87' SE 200sx/s12 (vg30e) . i have the complete unit sitting, i have all my adapter plates, brackets, etc, etc made, but i have one last thing to do...thats the bypass valve. now its gonna be a complete pain in the ass to plumb and i was wondering if its kosher to run a BOV on a blower? sorry, this might be a dumb question, but im a turbo guy and blowers are fairly new to me. anyhow, i have a BOV sitting on the shelf and this would WAY simplifiy my install. would it just be constantly making a 'blowing off' sound as the engine would be turning the blower? could i just put the TB after the blower? any info would be greatly appreciated!! thanks in advance

 

Yes, it will work,you mount it the same way you would on a turbo application.:icon46:

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Guest Jason84NA-T

You don't really need one for a roots type blower because there's no compressor surge to deal with.

 

I thought most M90's already have a sort of bypass valve and actuator built on to the housing... at least mine does.

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it does have a bypass, but it'd be ALOT easy to plumb in a BOV then that bypass..

 

there will be a surge of vacuum or build of pressure of some sort depending on weather the TB is before or after teh blower the second i close teh throttle plate..hence there being a bypass valve. im just curious if its cool to run a BOV

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I'd use a recirculation valve because releasing metered air will cause air/fuel ratio problems. On top of that, you'll need to be able to adjust the spring a bit to where the valve will be constantly open under vacuum.

 

I believe the biggest reason they use a recirculation valve is to simply increase efficiency under part throttle/vacuum. Spooling characteristics won't change at all due to it being spun directly by the engine, unless the valve stays open then you'll see some issues.

 

I though most Eaton setups had an internal bypass setup... basically to where all recirculation is done internally where no plumbing is needed. Is this one not the case?

 

On the throttle body, I believe for the positive displacement s/c's to run properly, the throttle body should be before the s/c (i.e. throttle body, supercharger, manifold/engine)

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Everything depends on where you place your throttle body. If you put the TB before the S/C like most are factory designed then there is no need for a BOV. The internal bypass mechanism that mounts to the side of the SC will control the boost by "sealing" the chamber when you go off vacuum (hard on the gas) and open when you go under vacuum (cruise and idle). This will work perfect with the MAF as well. If the TB is located after the supercharger then you have to have a BOV between the 2 in order to vent the pressure when the throttle plate slams shut (letting off of the gas). If not this pressure will back up into the SC because it has no place to go (even though the SC bypass is now open and thus not making more boost) and apparently they really don't like that! The tradeoff is the fact that the closer the TB is to the intake the better for throttle response.

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