Blow off valve (dump valve) questions

I'm planning my first turbo installation, and I need a little help with the blow off valve. Forgive me if these sound like dumb questions...

1. Do you have to fit a blow off valve? With an internal wastegate in the turbo, is it still common practice to have a blow off valve as well?

2. Does it matter where its located, or is anywhere between the intercooler and the throttle body OK?

3. I'm hoping to use quad throttle bodies mounted directly to the head. This gives no take-off point for inlet manifold vacuum. If a blow off valve is supposed to take a signal from the inlet vacuum, where can I route the pipe? I'm guessing that it can simply go to atmosphere?

Any help from you knowledgeable folk would be appreciated.

you dont have to use a dump valve, it could go either side of the intercooler and yes it needs connecting to the engine side of the throttle bodies, that way when you shut the throttle teh vacuum in the inlet manifold will help open the dump valve and when under boost the pressure will help keep it closed

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Originally Posted by Graham

you dont have to use a dump valve, it could go either side of the intercooler and yes it needs connecting to the engine side of the throttle bodies, that way when you shut the throttle teh vacuum in the inlet manifold will help open the dump valve and when under boost the pressure will help keep it closed

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Getting a vacuum line to the engine side of the throttle body butterflies is going to be tricky, but if I don't actually need a blow off valve, that would be problem solved! Cheers:thumb:

you only really benefit when using a lot of boost if that helps, i ran my race car with and without, and to TBH couldnt tell any difference

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Originally Posted by Graham

you only really benefit when using a lot of boost if that helps, i ran my race car with and without, and to TBH couldnt tell any difference

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I'm not likely to go above 1 bar / 15 psi max.

then in my opinion at least, its not needed, and one less potential source of boost/vacuum leaks

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Originally Posted by beeRS

I'm not likely to go above 1 bar / 15 psi max.

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Sorry to disagree with Graham but slam the throttles shut at high rpm and that's enough boost to stall the compressor / bend blades - see it with less boost and a U/S BOV. Also set up right it'll work off boost while vac is available as a priority valve. Surely taping a 1/8NPT nipple into an inlet tract ain't gonna be that difficult?

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Originally Posted by katana

Sorry to disagree with Graham but slam the throttles shut at high rpm and that's enough boost to stall the compressor / bend blades - see it with less boost and a U/S BOV. Also set up right it'll work off boost while vac is available as a priority valve. Surely taping a 1/8NPT nipple into an inlet tract ain't gonna be that difficult?

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perhaps, but i raced turbos for years without and never had a fail

I have thought about this but not for a BOV. I thought about making a sandwich plate which sits between the ITB's and head and tap each runner for an vacuum feed. There is a company on ebay that make flanges etc in alloy so could easily done. This is of course all theory so far , Or use a manifold and dcoe style ITB's then you can tap the manifold.

Good ideas guys. I spoke to the guys at AT Power today

https://s25.postimg.org/tdjp9whbz/ca...5d98078_1.pngw


The good news is that they have blind holes in each of the 4 runners. They are already tapped 3/8"BSP - you just have to drill them through. I was surprised because the throttle butterflies look so close to the mounting surface.

Just to be safe, I'll fit a dump valve.