I would like to get rid of the Hks dump valve on my 1998 impreza type r and wondered what spec/turbo it becomes nessercary to actually need one.
I have had lots of Cosworths and a dump valve was only needed when you used a T4 turbo or similiar which meant only 450bhp+ cars needed them. When the Cosworth sierra came out,in pre sale testing the general view was that they did not like the noise of pressurised intake air hitting the compressor wheel (rally style chirping) when the throttle was closed,so they fitted a recirclating dump valve. The recirclating dump valve removed this noise and was virtually silent but lead to problems of boost leaks when it wore out.
A lot of the top cosworth tuners say that anything under a T4 turbo will not be damaged by not running a dump valve,even the T34 running 30psi is ok from my experience.
What is the general view from the Impreza tuners??? I would imagine any turbo not capable of running over 400bhp will be fine without a dump valve?, especially as the impreza seems to run lower boost levels than similiar Cosworths.

regards mark

 

what turbo do you have at the moment?

the td05 series turbos can supposedly handle no dump valve, the ihi vf series turbos can not (especially the vf2X versions)

 

I have the standard vf23 fitted but will be fitting a td05 16g in the very near future and running around 330-340 bhp

regards mark

 

16g will be ok, vf23 will explode (like mine did )