turbo/supercharging

[Johnny]

Stephen Dubovsky wrote:

> Now I don't want to start a flame, but you aren't getting something for
> totally free here.  A turbo raises your exhaust back pressure (by as much
> as the boost I seem to remember someone saying - or close enough;) and the
> power your engine has to use to fight that back pressure is volume*dP.  And
> guess what, the power reqd to compress the air at the intake is volume*dP.
> Your engine has to work harder to get the exhaust out.  For ex: A 3.0L @
> 6000rpm w/ 1.0 bar boost and assuming 100%VE takes about 20-22kW of power
> compress the air.  Neither a SC or TC is perfect (I seem to remember 60-80%
> over a wide range) so your up to 25+kW.  This power comes from somewhere.
> A SC takes it from the crank directly and a TC from the exhaust pressure.
> Granted, the ~20 horses you lose will get you another 200+, so the net gain
> is worth it;)
> SMD

The other factor is that with the turbo, you can get away with less
muffler, and if you are running cats, way less muffler. So with an
exhaust system designed with turbo in mind, the back pressure can be
almost just the turbo itself, not the turbo + the rest as it would have
been without it. 

Blowers still look cooler though.  ;)

-j-