I have been puzzling over this for a while. Can anyone tell us the relationship between the Dawes,bleed hole,and the wastegate. I assumed that the Dawes allowed manifold pressure to the waste gate actuator to open it according to the selected boost required, and that this is controlled by the spring and ball valve. If this is right, I dont understand why a smaller bleed hole allows the turbo to spool more quickly, it feels like the opposite would be true.

Les

 

the bleed hole is after the ball and spring not before so will not have an effect on spool!

 

The bleed does have an effect on spool up because you are converting a pure ball/spring into a hybrid ball/spring and bleed.

A ball spring is an active pneumatic component (effectively closed loop with less influence from RPM/throttle) and the bleed is a passive pneumatic component so more open loop. It is not so simple since the wastegate itself is a closed loop device when connected to a boost source.

A bleed dumbs down the aggressiveness of the control - therefore you get less aggressive bottom end spool up, less part throttle boost, and less boost spiking.

Early spool up is favoured by using a very high wastegate solenoid duty cycle to reduce wastegate creep. A Dawes does a similar thing. A large bleed hole makes it more like a bleed valve. If you make the bleed hole 2.0mm you will have to have the ball spring very slack to actually keep the boost down, and the response will be very soft.

 

Thank you John,I think I see it now. I did not realise the effect of the bleed hole/ball valve combination. I have of course proved it to myself practically as you will have seen in the other thread.
The spool up of the TD05 is still not as fast as the smaller turbos going by the claims others make for boost/rpm figures.

Les

[Edited by Leslie - 7/21/2003 3:51:48 PM]