Blow Off Valve Question

premo-s12

Registered User
so im doing a custom install w/an eaton M90 on a car thats NOT a t-bird. i got 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 ~~~ 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? any info would be greatly appreciated!! thanks in advance
 
Wont work. Blow of valves are usually used in applications where the intake before the throttle is compressed (Centrifugal superchargers). A roots type blower like the M90 is directly tied to the speed the crankshaft runs at. What motor is this going to be mounted to? There was a guy that had his 5.0 supercharged with an m90, kept blowing off his IC lines and others. He didn't know why.............he never installed a bypass valve.
 
Really depends on how you have the blower plumbed. Throttle body before or after blower, MAF before or after blower ?

David
 
throttle body will be mounted before the blower as will the MAF. coming off the charger its running to the cooler then straight to my intake plenum via an adapter plate i made (where my old TB was). perhaps i should put the TB after the blower? and left my MAF before?

here's some basic info on my car

is an 87' 200sx/s12 SE (not to be confused w/the crappy sentra). it shares the same drivetrain as a 300zx (3.0L V6 vg30e), same rear subframe, larger brakes and a 280zx front end...but its HEAPS lighter then a 300zx ;)

anyhow, any input would be awesome!
 
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More than likely it would be something like this:
s/c-valve-throttle body-maf - I think this may also result in a very loud blower.
I don't think the stock s/c maf is real good for a blow through configuration.
Mike
 
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All you need to do is place the BOV between the blower outlet and the manifold inlet. Problem is that everytime the BOV opens it will be venting metered air to atmosphere causing a temporary rich condition. It would work much better if you used a bypass valve tying the inlet and outlet of the blower together when the motor is in vacuum.

David
 
David Neibert said:
Problem is that everytime the BOV opens it will be venting metered air to atmosphere causing a temporary rich condition.

well, wouldnt that be the case with all turbo engines running BOV's then?
 
Is the BOV located on the intake before the MAF on turbo cars? If so, then the air vented wouldn't be metered air and thus would cause a rich condition. I think for your applictation, it would work best if the supercharger is set up the way it is on the Sc, with the bypass valve.
 
its located after on turbo applications, just before the throttle body. i know id be better off to run the bypass but its gonna be a REAL pain in the a** the way things are goin..
 
Why not just go turbo or centrifugal? Putting a roots blower on an EFI car is no walk in the park.
 
ever look under the hood of an S12 w/a VG30E?? the engine hardly fits in there as it is. actually, minus this bit with the bypass/bov situation its been a cake install.. still waiting on some hardware from mc mastercarr and a belt tho..
 
premo-s12 said:
well, wouldnt that be the case with all turbo engines running BOV's then?

My turbo SC had a blow thru MAF (after turbo) and the BOV was located before the MAF. I've now converted to a 3 bar MAP sensor so it doesn't matter where the BOV is located. Some people using turbos with a draw thru MAF do vent to atmosphere and some use a recirculating bypass valve.

David
 
I know of alot of BOV's that actually come with a little nipple, that you can run a vacuum tube back into the inlet instead of venting to atmosphere.

You dont get the super loud PSSSHHHHHHHH but the sound is there.

BTW, whining is way cooler than pshhhhing
 
is there any reason that you can't use a blow through MAF with a supercharger?
I would say, use a blow through MAF, and put the BOV between supercharger outlet and MAF. Then you wouldn't loose any metered air, and you wouldn't need to worry about going rich at all
 
xThunderbirdSCx said:
You dont get the super loud PSSSHHHHHHHH but the sound is there.
BTW, whining is way cooler than pshhhhing
lol. i dont care about the coolness factor of a BOV as the blower in its entirety will be petruding from a whole in my hood! LOL

91supacoop said:
is there any reason that you can't use a blow through MAF with a supercharger?
I would say, use a blow through MAF, and put the BOV between supercharger outlet and MAF. Then you wouldn't loose any metered air, and you wouldn't need to worry about going rich at all
thats what i was getting at. i think ill plan on using a bypass till i get it mounted and it turns out to be a real pain in the a** ill re-route my stuff for a BOV.

im still waiting on my hardware from mc master carr to mount this thiing. arg, taking AGES!! i guess ill find out once i actually get it physically mounted what will be easiest, which will hopefully be sometime in the next day or two.

thanks for all the input and advice guys, been a real help! ill post some more pics when i get it mounted and go from there i guess.

here's the place ive been documenting the progress at if you're interested:
click me
 
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Is it going to be street legal with the blower sticking out of the hood that way? It's going to be very hard to see around, from the looks of it.
 
naw, it shouldnt be to bad really. its just the angles that make it look bad. the engine actually sits pretty low. only time will tell i guess
 
bov

put the blow off before the maf and you want have a problem just make sure that it is a blow through maf. just set it up like a centrifugal. s/c to bov to maf to throttle body. just put a filter on the inlet of the s/c. this way none of the air is metered before it blows off and it will be easier to tune.
 
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