Buying my first scooby
18 July 2004, 04:13 PM
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Buying my first scooby
I went to test drive an impreza 1996 2.0 turbo today, if all is ok with the paper work i will have it by friday. My first question is how much and how to get a dump valve fitted (really love the sound) second what is the point of a dump valve and third how do i know whether it's awd or not? Thanks in advance
regards Buzz
regards Buzz
18 July 2004, 04:34 PM
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Right, time for greasemonkey.
If you like the sound of a dumpvalve then go for it (and get ready for the boy racer comments), but the sound has no technical benefit.
A turbo pressurises the air, at high revs with throttle wide open, you have a large mass of air moving very fast down the inlet pipes. When you snap the throttle closed, that air is still moving. It piles up into the throttle plate and stops and its pressure ramps up, it then turns round and flows back up the inlet into the turbo. This backflow stall's the compressor, slows it down and can break it. The high peak pressure can also blow off hoses. Some turbo cars (200SX for example) do not have a dump valve as the flow rate is not high enough to cause a problem.
The dump valve dumps the excess pressure and thus prevents the negative flow of air backup the inlet. The standard scoobyone dumps it to the inlet and so is quiet.
A VTA dumps it to air and makes the whoosh noise, however, this air has been metered by the ECU then lost so it can affect briefly the fuelling.
Forgot to mention, unless you increase boost pressure or the original is knackered, a new DV is unlikley to give any benefit in performance or reduce lag at all.
If you like the sound of a dumpvalve then go for it (and get ready for the boy racer comments), but the sound has no technical benefit.
A turbo pressurises the air, at high revs with throttle wide open, you have a large mass of air moving very fast down the inlet pipes. When you snap the throttle closed, that air is still moving. It piles up into the throttle plate and stops and its pressure ramps up, it then turns round and flows back up the inlet into the turbo. This backflow stall's the compressor, slows it down and can break it. The high peak pressure can also blow off hoses. Some turbo cars (200SX for example) do not have a dump valve as the flow rate is not high enough to cause a problem.
The dump valve dumps the excess pressure and thus prevents the negative flow of air backup the inlet. The standard scoobyone dumps it to the inlet and so is quiet.
A VTA dumps it to air and makes the whoosh noise, however, this air has been metered by the ECU then lost so it can affect briefly the fuelling.
Forgot to mention, unless you increase boost pressure or the original is knackered, a new DV is unlikley to give any benefit in performance or reduce lag at all.
Last edited by Gary C; 18 July 2004 at 04:46 PM.
18 July 2004, 04:55 PM
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Thanks for the quick replies, yeah i wanted a dumpvalve for the noise but after reading a few threads on the forum i have almost talked myself out of it. I drove the car today and the turbo was awesome the guy is coming over to do the paperwork later. Is there anything important to look out for when buying a scooby 2.0 turbo? Thanks again
Buzz
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