club.liberty.asn.au

Ok I’m trying to sort out a few things prior to my car going onto the dyno very soon. One of which is trying to understand the operation of the dump valve.

Please correct me or tell me why it operates in the way does.

I totally understand that when you lift off the throttle the pressure in the inlet tract is released thereby preventing the turbine from stalling and adding shock loading back onto the shaft.

What I don’t understand is why the dump valve is open when the inlet tract is under negative pressure and it only closes when there is a positive pressure in the system?

Especially from a supercharger perspective where boost is being added continually as the revs rise, surely it is better to maintain this pressure until the throttle is released?
Under the very limited testing I can do at present due to keeping the revs sensible when I set the dump valve to open at idle the engine makes 2.5psi less at my imposed rev limit than it does when I set the valve to be closed at idle!

Maybe these type of dump valves are good for turbo installs rather than supercharged but even the supplier of the sc suggested using a Forge Motorsports supersize dump valve, and as far as I can ascertain that also works in the sameway?

Please enlighten me.

The BOV should only open briefly after you let off the throttle.

The wastegate would operate as required to maintain a boost level.

Not sure why yours is acting strange.

Mcmtv2 has good videos about this . Search for "go fast Brett on youtube".

Thanks only covers turbocharged application.

A bov or dump valve doesn't serve the same purpose on a supercharged car as it does on a turbo car.

In a supercharged car, a dump valve is used to regulate boost on idle generally. Ie, when your engine is idling its still spinning the charger which is creating boost against a closed throttle plate. If this has no where to go, you can see how it will be a problem.

Thus you will see it mostly open, and since it should be recirculated to your intake pre supercharger, should not create a boost or vacuum leak / or shouldmt have a negative effect on the supercharger system, even when on boost

Hope this makes sense

Mick

dr20t wrote:A bov or dump valve doesn't serve the same purpose on a supercharged car as it does on a turbo car.

In a supercharged car, a dump valve is used to regulate boost on idle generally. Ie, when your engine is idling its still spinning the charger which is creating boost against a closed throttle plate. If this has no where to go, you can see how it will be a problem.

Thus you will see it mostly open, and since it should be recirculated to your intake pre supercharger, should not create a boost or vacuum leak / or shouldmt have a negative effect on the supercharger system, even when on boost

Hope this makes sense

Mick

Thanks Mick it does make sense, my only observation about this is that unless on WOT there is still only a couple of psi at most in the inlet tract. I will be checking the functionality of my bov as I'm not 100% it works in the way it's meant to. Otherwise I wouldn't have been able to observe such a pressure difference between 2 settings.

On one of the GFB videos they talk about the Bob being closed and only opening when you lift of the throttle.

Thanks again.

Right i have checked out the BOV and it works as Mick described, the only thing I am unable to test is what psi it can with stand before being opened by the rising pressure in the inlet tract .