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Discussion Starter · #1 ·
having seen 2 polo g40's running dump valves, can they be fitted to a g60 lump?

and will they do any good? cos the charger is being worked on soon so the engine will be running around 200 bhp at the flywheel.:confused:

637 Posts
'borrowed' this from SMC News, it'll give an idea why dump valves are good for turbos, it'll also show how a turbo differs from a mechanical (driven) supercharger. make your own minds up :D

Bang, bang, chirp, chirp By ½ Clue
Streetly Motor Clubs resident semi-expert here. I know a lot of you spectate on rallies, I also know a lot of you compete on rallies. Well I thought I’d clear up a lot of noises for you and how turbo chargers basically work too!
Well here goes the rough guide to turbo chargers and the noises thy make!:~ A turbo is basically a small turbine that sucks air into the engine allowing it to produce more power, it is spun by the exhaust gases. When there are less gases being pushed through the exhaust ~ for example when engine revs are low ~ then the turbo spins slowly which in turn means it ‘creates’ little extra power, once revs rise there is a noticeable power increase. The wait between lots and little power is known as turbo lag. To help try and counter turbo lag technical wizards have come up with some clever idea cunningly called ALS or an Anti-Lag System. When the throttle pedal is let off ALS alters ignition timing along with fuelling, resulting in fuel rich air making it’s way into to the combustion chambers. Thanks to the altered timing most of the mixture makes its way to the exhaust vales and out into the manifold before igniting. By igniting in the ‘manifold’ area it keeps the turbo spinning freely as the ignition is immediately prior to the turbo itself. This rush of exploding gases compensate for the fact that the actual exhaust gases themselves are lower because the car is no longer on power. Combining ALS with a dump valve helps keep turbo lag to a minimum, a dump valve works very much along the lines as how it sounds ~ it dumps excess air from the turbo out of the manifold when the throttle is in a closed position. This stops the turbo blades from stalling helping to reduce lag.
The final part of the turbo equation is the wastegate. Made famous by the chirping sound it makes (on Fords particularly) this little device keeps turbo and engine life to a maximum by allowing excess exhaust gases to pass through to the atmosphere by the exhaust alone, bypassing the turbo itself. Thus under full power there isn’t a massive build up of exhaust gases through the turbo, hopefully preventing it from destroying itself ~ and possibly the engine along the way! Basically the wastegate is a flap held shut by a spring, when ‘air’ pressure is greater than the pressure the spring exerts it opens and gases escape.
A turbo provides plenty of horsepower and they are an integral part of rallying and there is a massive amount of time, engineering and money invested in them to give more and more power. For example the turbo on Per Eklund’s rallycross SAAB is hand built and designed to expand slightly, the blade tips are estimated to reach mach 2-3 under full power! Scary stuff.
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