does a turbo car 'need' a bov?
 

I was curious if it really did anything besides make a cool noise. I mean, yes i have one, the apexi dual chamber. For a long time i was just curious if one was even needed. If that be for reliability or for performance.

your thoughts/inputs?


-Marshall

It does make a cool noise, but that not its purpose. When you are under heavy acceleration and the turbine is pumping air into the throttle body/intake whatever, the little "butterfly" valve is open, letting this air flow through. Then when you get off the gas quickly, the little butterfly valve closes immediatly, but the turbine is still spinning, and thus pushing air, but the air has nowhere to go now. So the BOV does 2 things....

1. Reduces manifold pressure (i think)
2. (the main reason)... when this butterfly closes, the air still being forced at it bounces back and slow the turbine, so when you get back on the throttle in the next gear, the turbine isnt caught up to where it sould be and not making optimum power. The BOV filters all this air that has nowhere to go into the atmosphere, so the turbine stays spinning and it right there when you get of the throttle in the next gear. Sorry if that was vague.

Not a turbo expert as you can see... correct any mistakes.

If the valve is closed the forced air has no where to go and is consequently forced back on the turbines causinga lot of stress. This would eventualy lead to catastrofic turbo problems.

there's a big discussion on it here
http://ausrotary.dntinternet.com/for...&highlight=bov

a BOV is not needed for turbochargers to function, but knowing what we all know now, they are definitely recommended for the sake of reliability.

spec Rx-7 22 covered the important thing in #1. it relieves manifold pressure which would eventually lead to what Xteq said ... turbine stress. there have been several cases where the turbo shaft has physcially broken as a direct result of this "stress".

Just think of how long it would take for the engine to pull a vacume and rev down without a pressure dump. You would redline every time you shifted.

stops back pressure from killing your turbo. when you let off the gas the turbine is still spinning, but the boost is closed off from the intake manifold when you let go of the throttle. the air has to go somewhere, and the bov is where it goes. a bov also allows a turbo to keep spooling at higher rpms. if you didnt have a bov, the turbo would slow down dramitacly due to the back pressure, therefore venting the air allows the turbo to keep spinning.

Some sort of BOV is a must on a turbo'd car. One that makes cool noises, is just a cool novelty. Almost all stock BOV's dump the air back into the intake stream, so you can't even hear it.

for a street car yes you need one. some rally cars run extremly small ones and operate in compresser surge to help even out the torque response by keeping some boost.

need bov so the it can recirclelate all the boost air out when in boost. that's when you hear the whooss. so it won't go back to the turbos resulting in DEAD TURBOS...

They are really for reliability

A lot of Turbo Road Race cars do not use BOV...it keeps the air pressurized better for that boost of acceleration when exiting a turn

a lot of the Race Porsches I used to work on had no BOV for that reason....they also used only oil cooled turbos...which they would replace every season

for drag racing you should have a BOV....but for all out road racing you are better off not having one..unless you are really wathing the life of your turbo

short answer NO... read ausrotarys topic its a good read...

Think about that for a minute.

You slam the throttle shut. You have manifold vacuum... period. The engine's revving and it can't get air because the throttle is shut. Just like if the air pressure in the piping leading to the throttle body were 14.7psia (aka 0psig) just like naturally aspirated.

Practically all American turbo cars did not use BOVs. The trend really started with the Japanese when they started using really tiny little turbos for low RPM response, that had to spin super fast to be able to flow enough/create enough pressure ratio (remember, the two are intertwined with a turbocharger) at the top end. That is a *lot* of rotating inertia compared to a bigger turbo running much slower, and the smaller turbos also have smaller bearings to deal with the thrust loads.