On the Gen2 Coopers S turbo, built into the turbocharger housing, is a bypass facility. This allows charge air to be recirculated around the turbocharger from the boost side back to the intake side. This recirculation path is opened and closed by means of an electrical connection from the engine management to a solenoid that is mounted on the turbocharger housing. As you accelerate, the turbocharger vanes spin and therefore boost pressure increases (increases air flow to the engine). When you change gear you take your foot of the accelerator momentarily, select the next gear, and accelerate again. As you take your foot off the accelerator the throttle valve to the engine closes. The problem here is that during this process the turbo is still spinning and the boost pressure that it is producing has no where to go. (This is a bit like putting you hand over a hair dryer so the air cannot get out – not recommended!). What happens at this point is the turbo starts to stall, the spinning vanes slow down (incurring high stress) and the boost pressure drops. When you open the throttle valve again by pushing down on the accelerator (driver demanding more power) the turbo has lost its momentum by loss of boost pressure which then causes a pause (lag) until the engine produces the required power once again to spin the turbo. To combat this loss of power and stress on the turbo, a recirculation or diverter valve is used. On the Gen2 Cooper S, when the throttle valve closes, the engine management opens the recirculation route around the turbo. This gives the charge air an alternative route and allows the turbocharger to keep spinning so that when you accelerate again there is no pause (lag). This system works well and is adopted by nearly all vehicle manufacturers on turbocharged petrol engine applications. The only downside to this system is that turbochargers produce heat (the cooler the air, the higher the power gain). By recirculating the hot air back into the intake side of a turbo the temperatures increase. This is where the Forge Blow-off adapter (dump valve) plays its part by replacing the recirculation or diverter valve. By expelling the charge air to atmosphere rather than recirculating it, you do not increase the intake air temperature and you do allow the turbo to keep spinning. The side effect of the blow-off valve, which is unacceptable to most vehicle manufacturers, is the noise of the valve expelling the air (which is why they are not fitted as standard).
Fitting the Forge Blow-off adapter between the existing solenoid and the turbo housing involves removing only 3 bolts.
It should be noted that the engine management also uses this valve to decrease engine power when necessary. An example of this is by the (DSC) Dynamic Stability Control system. Although you would not normally hear this occurring, when a blow-off adapter is fitted you may well hear the air being expelled when the DSC operates (for example - usually when entering a corner too fast).
This adapter will fit all Cooper S and JCW Variants for the R56 N14 engine built between 2006 & 2008