Well, it may not make loud noises but I have learned something very interesting about how the bypass valve works on my car.

Instead of operating off the total boost pressure and venting when it goes too high it has a much better method of managing boost pressure at the same time it improves turbo performance.

On my 930 the bypass valve works not just off the boost pressure but also the pressure difference between manifold pressure and boost pressure.

For this reason if the throttle is fairly closed but the turbo is trying to spool up it opens up so the turbo will encounter less resistance and spool up more quickly than it would if the flow was being blocked.

This bypassed flow is also fed back through the intercooler again which improves the thermal efficiency of the intercooler system.

I will post a pic of this strange piece of plumbing as soon as I have a chance.

Ah, the interesting things you can learn when taking your engine apart and looking over technical documentation.

 

u lost me back at manifold pressure

 

ya im lost too. i dont see how boost and manifold pressure are diffrent. other then some pressure drop but i dont see how thats related to spool up time.

and why does it seem that you are talking about the blowoff valve and the waste gate at the same time?

 

A bypass valve is like a blow off valve, but instead of venting boost into the atmosphere it sends it back into the turbo intake (which keeps the air meter from getting screwed up readings).

Manifold pressure and boost pressure are often different since there is a throttle between the turbo and the engine.

For this reason your turbo could be making boost but if your throttle is closed enough there is less pressure (or even a vacuum) in the intake manifold.

In the situations where this occurs my wastegate opens so there is less resistance to the turbo so it can spool to a higher rpm which will come in really handy when the throttle opens up.

The only thing the wastegate does is limit the exhaust gasses to the turbo so it does not overboost.

 

ok you make more sence now, or is it just that ive had sleep now... anyhow it still seems like you are talking about only one part. in the orginal post but really you are talking about two.

 

cool

 

I need a turbo glossary. I always refer to the waste gate as the bypass. I think in terms of exhaust bypassing the turbo and exiting straight out the pipe. I guess what a lot of people call the bypass, I think of as a blowoff valve, since it's function is to prevent excess pressure on the compressor wheel when the throttle blade is closed, therefore it blows off the pressure.

All I know is that it makes a lot of noise when it spools up.