dump / BOV's
 

Has anyone heard of running a turbo charged engine with out a dump valve or BOV?

Reason: I was recently told by my local scooby tuner that it is poossible they had done it to a few impreza's and evo's... even the bosses 350bhp classic impreza... BUT he couldnt go in to any details at that time cos they were short staffed and they had to get an engine out asap, so i'm sceptical.

chris

the basic thing that a dump or Blow Of Valve does is to get rid of the inlet charged (boost) that is present between the compressor and the butterfly/ies.
it works only when u suddenly close the throttle, cos then the butterflies will close resulting in a higher pressure on this part of the plumbing that results in slowing down the turbo. Basic rule of physics: everything that goes in has to come out. since it cant come out it will not get in, in the first place.

IMO running without a BOV will result in increased turbo lag. i would "justify" not using one if your turbo is really small, that stays in boost or really close when u shut the throttle. but what is the point of running a really small turbo? u will get poor performance due to extremely high temps .dont forget that the engine is basically an air pump...

Chris

It will only cause increased lag between shifts, though this is where you don't want lag. Also not running a blow-off valve will shorten the life of the compressor. The pressure wave that propagates when the TB is closed and after being on full boost makes its way back to the turbo and can cause compressor surge. The main thing though is keeping the pressure wave away from the turbo so it stays spooled for the next shift. Now I'm not sure about carburated turbo setups. I know diesels don't need a BOV because there is no throttle body. Turboed automatic cars and drag racers who speed shift also don't need them because the throttle doesn't close during shifts.

Mike