Dump / BOV / Wastegates
- Thread starter ramirez
- Start date
. Will get round to buying an after market recirc eventually.
Argh too much 'manufacturer' marketing BS floating around guys, seriously! 
I'm talking in excess of 30psi/80,000 miles before I'd worry about turbo longevity!
Seriously, a well looked after turbo with a good 360 degree bearing will take a lot more 'none dump valve' abuse than you think!
Oh, and a turbo really doesn't stall that easily. Dump valves don't dump the 'excess' boost to atmostphere, they dump everything in the boost circuit to atmosphere. Because of that, it has to produce all the boost all over again regardless - which causes a loss of throttle response. Unless of course you do a seriously quick gear change (or flatshift) or have a massively long boost circuit...
When you don't have a valve, the only place the air can vent is back out through the turbo. Since the turbo is spinning at about 150k rpm, the air finds it a bit more difficult to vent so the boost circuit holds the pressure a bit longer - which helps throttle response. If you watch a boost gauge when you come off the throttle without a valve you can actually see this. The gauge will flicker and generally stay higher than with a valve - which will empty away your boost almost instantly. This was certainly the case with my GTT. I only had a SSQ for the noise - when I was doing anything 'serious' like a track day I'd always remove it and put my bypass pipe in.
I'm talking in excess of 30psi/80,000 miles before I'd worry about turbo longevity!
Seriously, a well looked after turbo with a good 360 degree bearing will take a lot more 'none dump valve' abuse than you think!
Oh, and a turbo really doesn't stall that easily. Dump valves don't dump the 'excess' boost to atmostphere, they dump everything in the boost circuit to atmosphere. Because of that, it has to produce all the boost all over again regardless - which causes a loss of throttle response. Unless of course you do a seriously quick gear change (or flatshift) or have a massively long boost circuit...
When you don't have a valve, the only place the air can vent is back out through the turbo. Since the turbo is spinning at about 150k rpm, the air finds it a bit more difficult to vent so the boost circuit holds the pressure a bit longer - which helps throttle response. If you watch a boost gauge when you come off the throttle without a valve you can actually see this. The gauge will flicker and generally stay higher than with a valve - which will empty away your boost almost instantly. This was certainly the case with my GTT. I only had a SSQ for the noise - when I was doing anything 'serious' like a track day I'd always remove it and put my bypass pipe in.
Bear said:
Agreed - Audi originally introduced quiet recirc valves on their turbo cars back in the 80's since customers were returning their cars saying there was a problem with the car - a noise every time they backed off the throttle. Yes - compressor surge.
Just to concur with everything Lowe has said. Factory fitted BOV/Dumpvalves are for one thing only: To surpress noise caused by compressor surge.
Indeed, a lot of munufacturers list the part as 'noise surpression device'.
Indeed, a lot of munufacturers list the part as 'noise surpression device'.