vwdsmguy
Veteran Member
I been reading about Exhaust Manifold Pressure and how a small turbine side can raise EMP well up there. Anyone measure the VNT17/22's EMP?
TDIfreak relates to this, I think.
Join Date: Sep 2001
Location: Finland
Re: GT17/20 non-vnt hybrid?
There are no 'better' or 'worse' flow, but there are IMO three (and only three) variables that count:
boost
intake air temperature
exhaust manifold pressure
They tell you relatively how many oxygen molecules you get into the engine for burning the fuel dose. They are all linked together and both IAT and EMP (relative to boost) tell when you have correctly spec'd turbo.
If you can make the boost with the small turbo, you are only going to achieve anything by lowering IAT and lowering EMP with bigger or better sized turbo.
High IAT you can make a lot lower with good intercooler, so that the temp difference produced by different size turbos becomes very small. It's always there and in some cases it's meaningful and in others, not.
High EMP is said to kill turbos and raise exhaust and engine temp. High EMP is partly due to the inefficiency of the turbo and with vnt-turbos it tells you when the turbo is too small; boost creep is high EMP's best buddy.
TDIfreak relates to this, I think.
Join Date: Sep 2001
Location: Finland
Re: GT17/20 non-vnt hybrid?
There are no 'better' or 'worse' flow, but there are IMO three (and only three) variables that count:
boost
intake air temperature
exhaust manifold pressure
They tell you relatively how many oxygen molecules you get into the engine for burning the fuel dose. They are all linked together and both IAT and EMP (relative to boost) tell when you have correctly spec'd turbo.
If you can make the boost with the small turbo, you are only going to achieve anything by lowering IAT and lowering EMP with bigger or better sized turbo.
High IAT you can make a lot lower with good intercooler, so that the temp difference produced by different size turbos becomes very small. It's always there and in some cases it's meaningful and in others, not.
High EMP is said to kill turbos and raise exhaust and engine temp. High EMP is partly due to the inefficiency of the turbo and with vnt-turbos it tells you when the turbo is too small; boost creep is high EMP's best buddy.