Lowe said:Couple of things that also need clearing up with this subject.
All this "dump valve stops the turbo from stalling" stuff is pretty much myth. If you run a dump valve of any sort you will experience a loss in throttle response compared to not running one at all.
When you come off the throttle with a dump valve in situe, the charge (compressed air) leaks away, usually to atmosphere. If you have a boost gauge attached you will see a smooth linear, boost drop until the level reaches zero. Depending on the boost being run, the valve in use and how fast it opens, this can take anywhere up to a second or so.
When you don't have a valve in place, the charge hasn't got anywhere to go apart from back through the turbo. But think about it - the turbo is still spinning at about 100,000rpm or so with the air coming IN to the system. The charge in the system is rushing out and the two pretty much cancel each other out, but with the charge leak will "win" since the turbo is starting to slow. If you watch this process on a boost gauge you will see a violent shuddering of the needle which very slowly reduces to zero. This takes a fair bit longer to equalise which is why you get the better response - because at any point when you nail the throttle again, there is already a bigger charge in the system, in turn giving you better response.
Now dump valve manufacturers will have you believe that this is a bad thing. They say it will destroy the turbo - this is NOT the case unless you're running silly boost. R5 GTT's will run 100,000 miles or more on the standard turbo without any difficulty, and they don't have one as standard. Audi only ever introduced them to road cars in the early 80's since customers kept returning cars saying they kept hearing a fluttering sound when changing gear! I ran a GTT at 18/19psi every day as a daily driver for 3 years without any kind of turbo problems. Hell, I've seen people run 30psi or more without a valve and not have any problems. Modern turbos with strong 360degree bearings just don't suffer from this kind of problem any more.
Saying all this though - I ran the Clio Turbo with an SSQ, but purely because I liked the noise. If I ever wanted to do anything serious I'd remove the valve and go without.
http://www.andrewlowe.plus.com/ClioPMTTurbo.mp3
Yes it's chavvy, but I loved the noise that car made when driven in anger.
Every new from factory R5 Turbo I have ever seen had a recirc valve as standarad. I worked in a Renault garage for over 10 years and have never seen a standard R5T without one of these.
I worked at Formula Palmer Audi as well for a while, using the Audi 5cyl 1,8 Turbo engine, and at the start running the standard turbo with no valve of any kind (we took off the standard recirc) we had a spate of a dozen or more turbos blow up due to stall, all running less that 11psi boost. We had to fit hybrid turbo's with forge recirc valves and modified wastegates to actually get the things to be reliable.
