BOV's simply stop the turbo stalling, the idea being that the excess pressure is vented and the turbo can spin freely.

Much better is a closed circuit recirculating system, which circulates the pressure from the downstream side of the turbo and injects it back in before the turbo impellor. These systems actually keep the turbo's spinning much faster than normal BOV's. Course you dont get the noise, but what do you want, performance or show?

In terms of damage, a BOV wont really protect or damage the turbo from anything, it's more than tough enough to withstand the stalling action. Ask a mechanic if he's ever seen a shattered turbo, answer will be no, then ask him how many times he's seen the bearings shot because the oil feeds clogged. Thats what kills turbo's, not the pressure issues.

Rally cars are totally different kettle of fish, they use anti lag systems which you'll never see on any road car, save for the handful of toyota WRC homologatoin GT fours. When the engine revs drop, the turbo begins to stall, as it does in normal cars, what then happens is that fuel is either injected just upstream of the turbo and ignited, giving an explosion which then spins the turbo up to full speed OR they run an extremely rich mixture through the engine as the throttle is shut down. Both systems require an air bypass into the manifold (or you wouldnt be able to ignite the fuel). Thats why when you see a WRC car they always bang and shoot flames from the exhaust on the upshift.

You couldnt do this in a normal exhaust, it would blow it to smithereens, and it's not kind on the turbo either, but then when you've got millions to chuck at a WRC car it doesn't really matter blowing a new turbo every race.

Hope that helps.

 

i always wondered what anti lag really was. no one could ever give me a good answer until now thanks man!