Whitestriped63 wrote:
My understanding was the BOV recognises boost levels (as close to the throttle body as possible), sends a signal via boost pressure to the wastegate actuator and that in turn opens the wastegate allowing unwanted boost to escape into the exhaust whilst keeping the turbo spooling.
I may have originally confused you buy saying external wastegate rather than externally located wastegate/wastegate actuator.
Check this out for a diagram!!!!!!
http://www.gcg.com.au/Technical%20Data/turbo_sys.jpg
Umm no! A BOV is seperate to a wastegate. The BOV will do what you say above but it is a single and seperate unit. When the throttle shuts the BOV will open to let air out of the tubing between the turbo and throttle body so it isnt forced back through the turbo and out the inlet.
An internal wastegate is located in the rear housing of the turbo. When the boost level is high enough to force open the spring in the actuator the wastegate will open letting boost out and around the rear turbine. This keeps boost at the required level.
An external wastegate is located externally to the turbo. It will usually sit between the turbo and the cylinder head on the manifold. This is referenced to manifold pressure like the internal gate and when the boost level is high enough the spring will compress causing the wastegate to open and let air pass around the turbo doing exactly what the internal gate does.
They do the same thing and the benefits of either are not huge IMO.
You can also run an external gate off the rear housing of the turbo by welding up a port onto the rear cover and running the wastegate off that. You dont see this too often though.