RWD_cossie_wil

iTrader: (9)

OK then, I don't know a vast amount about this subject, so If anyone wants to explain fully the in's and outs of it, I would appreciate it. But as far as I can work out, this is the general lay of the land putting in some (very) rough figures?

1) you measure back-pressure between the head and the inlet to the turbo turbine side, ie in the trouser legs of a 2wd exhaust manifold. Ideally backprsesure should always be less or equal to inlet pressure?

2) the less backpressure you have, the better it is for power.

So, ideally you want lots of nice exhaust gas to drive your turbine, so the compressor can supply enough air for your desired inlet pressure ( say 35psi on a T34, approx 45Lbs/min of air?) to the limiter. Obviously as turbo/engine RPMS rise backpressure will rise.

Obviously the smaller the turbine whee & A/R, the lower the RPM's will be for a given response level (aassuming a 2.0L YB engine), but will cause more restriction at higher engine RPM's .

But do you have top tail off the boost as engine RPM's get higher for a number of reasons,( injector duration, turbo over-speed etc) but for arguments sake, say at 35psi@ 7000 RPM the back-pressure through a T34.48 becomes too much? (ignoring compressor maps for a minuite) and running more boost is detrimental as the turbine and wastegate just cannot physically shift enough air?

Assuming back-pressure is the limiting factor for running high RPM boost on smaller turbos, would reducing backpressure at high RPM's increase power for no other problems, ie could you make a T34 hold 35psi to the limiter if you could keep back pressure down enough? ( again ignoring compressor maps)

RWD_cossie_wil

iTrader: (9)

Anyone?

Stavros

IMO people read far too much in to turbo backpresure. Of course it is robbing power compared to it not being there, but people stop going higher on the power because of it too soon IMO, which makes no real sense.

Many seem to stop when boost is equal with backpressure, even tho a lot of the fastest cars around have 2x+ backpressure compared to boost.

FFS, even in latest PPC that guy seems to make out if you got 30psi boost but 29psi backpressure you only really getting effectivley 1psi's extra airflow/boost, which is utter shit.