You can't really issue a blanket statement that you should run a larger plenum. That's like saying a larger exhaust will give you more power. Much like a larger exhaust, a plenum that is too large will decrease the velocity of air and yield lower hp. I don't believe he will need a larger plenum to yield the results he wants.

No you are right that he will not NEED a larger plenum, but being a common fact that forced induction motors should have approx 75% engine capacity in the plenum, tapered off to avoid barrelling at the ends (note: TB is located in centre of plenum..very messy air flow) (resonance plays no part with forced induction), the manifold is currently OFF the car, and theres been oh so much custom work, it would be a wise step, especially since the single turbo setup will mean a 'top endish' dyno curve. Its just something I would do if I were going that far. And yes a larger diameter exhaust is always positive with forced induction as %0 backpressure is as efficeint as the turbo can get.

So they want you to think. Road Race car maybe, low boost street car I would not worry. I dont have a BOV on my 18psi race car.

You don't need one on a race car or at least not one for short races, drag races, but you do need one on the street for compressor longevity, better mileage, and better driveability. A pressure activated pop off valve serves better for drag racing applications. On low boost application a BOV is not necessarily needed but your engine will operate better with one. However, if your blower is too small and can't make up for that release in air pressue quick enough then no BOV should be added.

I've run with and without and have seen first hand how much hotter the engine gets with no BOV even at lower boost levels. The gas mileage also goes to hell, without the BOV, because the blower is always trying to compress the air and can't free spin as it can with the BOV. Your car can operate under vacuum conditions, BOV present, and not cause drag on your engine unecessarily and you will get better mileage, better driveability, longer compressor life, and ........

..........just about every factory produced vehicle came out with a blow-off valve (actually, the proper term would be compressor by-pass valve). Just that they came with recircualting ones that dont vent to the atmosphere, hence a very very silent "pshhh".

Bosch made most of these. They are black, and take compressed air and re-route it to the intake pipe post filter normally (in MAF sensored cars) or pre filter in MAP sensored cars. They are a factory item in: Saab turbos, 911 turbos, Nissan RB20/25/30/26, CA18/ ET15, among zillions of others. Two of these from a wreckers will set you back $30. They work, are stealthy, and cheap.
You'd be nuts not to put a decent BOV on that new hybrid. You dont have to go the gay noisy ones (frankly, they draw to much attention and make you look a ricer), there are some fantastic stealth versions out there.

The race car aforementioned is fitted with either a pop off valve, or uses an external wastegate mod to vent the compressed air when throttle plate is closed. What kind of race car is it anyway? Sounds like a V8TT sprintcar.

Compressor surge sucks.

Hey!!!!


I have a Forge BOV and it sounds nice.