TURBO DUMP / BLOW OFF VALVES

We get many people ask for dump/blow off valves as they want to make their car make a noise like a high boost turbo car. Firstly, these valves can only be fitted to turbo cars and cannot be fitted to any normally aspirated car and there is something wrong if they are needed for a supercharged engine. On all standard turbo cars they have what they call a waste gate to stop excess boost pressure, as if they did not, the engine would blow up due to too much pressure. The type of waste gate fitted to standard turbo cars do this by venting the excess exhaust pressure, not boost pressure, to reduce the speed of the turbo and so reduce boost pressure and with this type of system no blow off valve or noise is heard.

The only systems where you have a blow off valve fitted is where for what ever reason the air pressure made by the turbo is in excess of what the engine is programmed to run on and the excess is vented to the atmosphere and so the noise heard. I am quite sure that many people fit them, not to safe guard the engine but just to make the noise to impress friends and to make it do so, loose power. If your engine has a standard turbo set up, the waste gate will regulate the boost pressure and so the only way you can make the dump valve operate is to set it to a pressure below normal, otherwise it would not work, the fact you are operating the dump valve means you are loosing boost pressure the engine normally operates with and so are down on standard power.

With a supercharger the size of the charger should be matched to the engine performance and because superchargers are mechanically driven you know the boost pressure rises fairly uniformly up to a maximum and as are utilising all this boost pressure you do not want to waste any. For those who insist on making "the noise", yes you can fit a supercharger that is far too big and waste all the excess air but it is an expensive way to produce a noise. The only time it maybe worth doing the above is if you wanted maximum boost low down the rpm range and then you would have to have a dump valve as the pressure high up would be too much. Having said this most people want the car to accelerate as quickly as possible from a standing start, what is the point of having massive bhp low down when all it is going to do is cause wheel spin and transmission problems.