A dump valve, or commonly known as a blow-off valve, is a pressure release system in turbocharged engines. It fits between the compressor outlet and the throttle, and it reduces the wear on the turbocharger, as well as the engine, by relieving the damaging effects of the compressor. It allows compressed air to either re-circulate or vent to atmosphere by bypassing the pressurized air on a closed throttle.
In order to install it, the vehicle must have a turbocharger or supercharger. Blow off valve kits are available for many models, such as Audi, Ford, Mitsubishi, Nissan, Subaru, and Volkswagen. Car manufacturers usually fit this for emission purposes, as well as fuel economy and drivability.
Most people who install it aftermarket do so for a boost level that is higher than the standard, for better throttle response, and of course, to make the blow-off hiss or whoosh noise.
There are two specific brands of dump valves. Bailey Motorsport offers a piston design dump valve, which has faster reaction time, increased boost capability, and it can work on cars with airflow meters. They sell either the single piston or twin piston Bailey dump valve if you are a noise lover. If you prefer a more quiet boost, they offer the piston-type recirculating dump valve. The prices range from $83.00 to $118.00, depending upon the style you prefer.
Forge Motorsport offers a variety of dump valves, as well. Forge maintains that their valves are designed and built with the intention of venting 100% of residual charge air to the atmosphere. They carry single piston and dual piston valves, as well as offering a re-circulating valve. Prices start at $138.00.
This can be fitted by several different modes. For example, a hose mount can be used, which makes it easier to replace, if necessary. A pipe mount can also be used by welding the base into position between the compressor outlet and the throttle. Vehicle specific flange adaptors are also available.
Installation of a dump valve is a personal preference. Some people, mainly car enthusiasts, love the hiss and whoosh sound made when the air vents to atmosphere. Others feel that there is no benefit to vehicle performance, and after a while, the noise becomes bothersome. It require a certain amount of maintenance, and this is another sore spot for some who do not care to spend the time under the hood, especially when they notice little performance benefit.
The main goal for installing this is to protect the turbocharger, and to date, it has not been shown to increase power. However, in some car models, an immediate change to the car can be felt, particularly when changing gears, due to the continued spinning of the turbo in closed-throttle conditions, thus enabling a quicker “full boost” to the car.