boost question??
11-24-2001, 01:03 PM
#2
Nordschleife Master
Wastegate is on exhaust and opens up to bypass exhaust gasses around turbo thereby slowing turbo down and reducing boost pressure. Without this your boost could go skyhigh and blow up your engine. Depending on wastegate and way things are set up this can also be a problem the other direction (too low boost pressure) when the wastegate starts to open up and cut boost level before you want it to. Which is why you see Lindsey boost enhancers, shims and such.
A pop-off recirculation valve is connected to the air intake after the turbo and before the throttle. As you accelerate hard under boost, pressure builds up in intake. When you go to shift and lay off the throttle the throttle shuts, turbo has less exhaust pressure driving it, the high pressure air in intake wants to go somewhere, so it slams back against the turbo. This slows the turbo down pretty sharply and you will have a noticable lag getting the turbo spun back up when you complete the shift and lay on the gas again. It is also hard on turbo's bearings.
So the pop off valve is installed to open and vent off the high pressure and keep the turbo spinning a bit better. A 951's blow off valve vents the air back into intake system between the turbo intake and after the air meter so as not to confuse the air meter too much into thinking the engine is using more air than it really is and having the DME run the fuel too rich.
I'm not sure if your 931 has a blow-off valve, not all turbos do. You might want to look at that and install one if it doesn't have it.
Whew!
A pop-off recirculation valve is connected to the air intake after the turbo and before the throttle. As you accelerate hard under boost, pressure builds up in intake. When you go to shift and lay off the throttle the throttle shuts, turbo has less exhaust pressure driving it, the high pressure air in intake wants to go somewhere, so it slams back against the turbo. This slows the turbo down pretty sharply and you will have a noticable lag getting the turbo spun back up when you complete the shift and lay on the gas again. It is also hard on turbo's bearings.
So the pop off valve is installed to open and vent off the high pressure and keep the turbo spinning a bit better. A 951's blow off valve vents the air back into intake system between the turbo intake and after the air meter so as not to confuse the air meter too much into thinking the engine is using more air than it really is and having the DME run the fuel too rich.
I'm not sure if your 931 has a blow-off valve, not all turbos do. You might want to look at that and install one if it doesn't have it.
Whew!