Since my first/last car was a Cobra, I never delt with turbos before and I am learning quickly but learning is learning. I know that the BOV releases the pressure when throttle is released. What is a wastegate?
Thanks in advance!!
Check out "How Stuff Works" for a great primer on turbos:
A BOV (Blow-Off Valve) and a BPV (By-Pass Valve) and a Diverter/Recirculator Valve are for the most part interchangeable terms for a device that relieves excess boost pressure. This device works on the clean air side... before it goes into the engine. Say an engine is happily boosting along with 15psi of pressure being feed into it. What happens when you take your foot off the gas and the throttle slams shut? All that happy flowing boost pressure now cannot get into the engine (throttles closed) and has nowhere to go. This causes a pressure spike on the clean air side which will surge (nearly instantaneous) back to the turbo and cause the turbo compressor (the part of the turbo pressurizing the clean air) to stall or slow down very quickly. So when you go to floor the gas (like say this all happened between a shift) and open the throttle again... now the turbo has to spool backup since it was stalled by the surge to give you your happy boost pressure. This device we're talking about relieves that pressure spike so it doesn't surge back to the turbo and stall it. A BOV will relieve this pressure spike straight into the atmosphere. They're the ones that make all those cool hissing/whooshing noises everyone loves. A BPV or Diverter/Recirculator will relieve this pressure spike but funnel it back into the clean air system where the turbo is sucking it in... instead of venting it into the air. Some BPVs will do both... recycle part of the pressure spike and vent part of it so you get a cool noise.
A Wastegate works on the dirty side... the spent exhaust coming out of your engine. As the exhaust comes out of your engine, it goes into the turbo's turbine housing (see link above for better explanation of turbine/compressor terminology). If there were no wastegate... all the exhaust would always be funneled into the turbine passing over it and spinning it like mad. You wouldn't be able to control boost... it would be an all or nothing thing. With a wastegate, however, when the turbo's boost pressure reaches the desired amount (as determined by the ECU or boost controllers) the wastegate is opened (using boost pressure to overcome a diaphragm internal spring) which opens a different route (a hole) in the turbine housing for the exhaust to flow through instead of passing over the turbine itself. So with exhaust now rushing out the wastegate hole (and out the remaining exhaust post-turbo) there is less exhaust rushing over the turbine to spin it, so the turbine achieves a constant desired rpm level and the boost pressure on the clean air side stabilizes (doesn't max out).
Does this make sense? The How Stuff Works link explains it really well with pictures and all.
Hope this helps.