Blow off valve on a Supercharger??

[Damo323]

Hey guys, was just wondering if you can put a blow off valve on a supercharged car? seen a couple of vids on youtube but they are on american pickups and it doesnt sound right.

Anyone got one on their car?? thats if you can. :hmm:

If so.... any recomendations?

Thanks.

:thumbsup:

[docwyte]

You can, but since the car runs a MAF, it'll run like crap since you're venting metered air to the atmosphere. You have to run a bypass valve that vents the air back in to the intake.

So you don't get the sound, which I assume is what you're after...

[Damo323]

Yeah you got it in one, ha ha, would love to have that sound. Take it its a no then..... :cry:

When you say it wouldnt run right, do you mean it will just run a bit lumpy n hardly do anything, or do you mean it will mess up performance and so on?

Cheers.

[docwyte]

It'll run rich. Don't do it.

[SteveX82]

It'll run rich. Don't do it.

No.

At a first theoretical glance, one might think that the car would run a bit rich for a fraction of a second when lifting off the throttle after a WOT run (for the reason docwyte covered). However, the engine won't fire the injectors or plugs when the throttle is closed and the engine is spinning above a certain RPM (likely in the 1400-1800rpm range). Consequentially, any atomized fuel that is traveling through your intake to combust with the air that you've just vented to atmosphere will simply pass through the engine and out your exhaust without incident.

The valve will be completely closed the other 99.9% of the time (idle, WOT, light acceleration, cruise, coast-down), and will therefore have no effect on how the car runs in daily driving.

FWIW, I vented my blowoff valve to atmosphere on a closed air metering system turbo car for years (with a VAM instead of a MAF, but they are effectively the same in relation to this topic). There was no discernible difference in driveability or wideband readings when running with or without the valve hooked up.

[Damo323]

Thanks Steve, thats a great help. :thumbsup:

Now i understand a lot more!!

Is there any certain blow off valve you would go for or are they all vertually the same?

Cheers.

[Activ3]

No.

At a first theoretical glance, one might think that the car would run a bit rich for a fraction of a second when lifting off the throttle after a WOT run (for the reason docwyte covered). However, the engine won't fire the injectors or plugs when the throttle is closed and the engine is spinning above a certain RPM (likely in the 1400-1800rpm range). Consequentially, any atomized fuel that is traveling through your intake to combust with the air that you've just vented to atmosphere will simply pass through the engine and out your exhaust without incident.

The valve will be completely closed the other 99.9% of the time (idle, WOT, light acceleration, cruise, coast-down), and will therefore have no effect on how the car runs in daily driving.

FWIW, I vented my blowoff valve to atmosphere on a closed air metering system turbo car for years (with a VAM instead of a MAF, but they are effectively the same in relation to this topic). There was no discernible difference in driveability or wideband readings when running with or without the valve hooked up.


The valve is opened partially during part throttle and idle with a supercharged car. Venting to atmosphere will most definitely alter driveability negatively on a supercharged car. I wouldn't recommend doing it.