[Diy_efi] New project- intake effect on VE on turbo car

[Grant Beaty]

> Wouldn't the same turbo unit spinning at a higher rpm create less of a
> restriction to the exhaust than a turbine spinning at a low rpm?

No. Remember the wastegate? It will be open more if less energy is needed to
drive the turbo. Therefor exhaust backpressure will be less. (I think)

To see how the compressor is effected by intake restrictions, look at its
compressor map. Garrett gives a nice definition of compressor effeciency as
"the percentage of turbo shaft power that converts to actual air
compression."

Grant

If the
> intake is super restrictive (think plugging your shopvac hose w/ a wad of
> duct tape), the compressor is in very sparse air (vacuum), so there is
> less restriction (less work to be done), and so it speeds up (you hear
> your vacuum speed up, and motor HP hasn't changed). If there is less work
> being done, there is less energy being taken from the exhaust, so it will
> be less restrictive. Granted - you'll be way down on HP since the
> centrifugal compressors work across a pressure ratio. No vacuum = ambient
> pressure about 14.7 psi, so a 2:1 pressure ratio would give you 14.7 psi
> above the ambient intake pressure at the compressor's outlet. If the
> intake is choked, the inlet pressure would be a significant vacuum. twice
> a significan vacuum = much less boost, which is much less air, which is
> less work, which is less of a restriction. If you want the same compressor
> outlet pressure, then, yes, you'll have to spin the turbine much faster,
> which could be by not opening a wastegate. Since you've got your turbo
> bypass closed (wastegate), there is more of a total exhaust restriction
> (but the turbo is the same restriction it was before).
>
>  > > There are more important reasons to have an efficient
> intake tract. > Primarily that you
> > a)want the turbo to be running at the lowest PR possible. PR is measured
> > on both the compressor inlet and outlet, not by the barometer on the
> > wall and the manifold boost gauge.
>
> A.
>
>
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