[s-cars] Turbo 101 question...

[mlp]

Tom, to make boost I believe you need at least two things (probably more,
but at least two for sure), i.e. (a) sufficient rpm to provide initial flow,
& (b) engine load to provide or turn that mass into vastly expanded gases
(i.e. heat) to that flow.

For boost purposes the two are interrelated.  I believe it's the engine load
that creates the necessary heat and ultimately pressure differential across
the hot/cold sides of the turbine that produces the boost you measuring on
your intake cold side.

I believe the problem with making max boost in 1st gear is you can't (this
should be sung, slightly off key, to the tune/lilt of "For Want of a Horse
Shoe Nail") get enough load, to make the heat that expands the exhaust
gasses, that turns the turbine that turns the compressor, that moves the air
that fuels the car that turns the engine that moves the wheels etc., etc.,
etc.

I've been told / read that the temperature drop across the turbine side of
your friendly K24 or RS2 is something like @ 300 degrees +/- under heavy
boost, which I guess is the energy that's being taped by the turbocharger
and used to feed more power, i.e. air & gas, into the car.

In 1st, I'm guessing the gearing is just too low, at least on a level road,
to provide enough engine load, to make the hot gasses needed to make full (?
18 psi or so) boost  before you run out of safe, available engine rpm.  If
you want to try for a higher peak boost number in 1st gear, I guess you
might try punching the car off in 1st gear on a steep incline.

Your AC adds to engine load in 1st gear (unless it kicks off.)  I still
doubt AC alone will get you to "full" boost (? 18+ psi) in 1st, but you
would probable see a little bit higher peak.

Mike P.


~-----Original Message-----
~From: s-car-list Pollock, Thomas
~Sent: Thursday, June 27, 2002 10:52 AM
~
~Afternoon, fellow s-heads...
~
~All the recent A/C discussions have prompted me to ask this
~question which I've always wondered about. In it's simplest form,
~why don't I see full boost in first gear ?  I guess the extreme
~would be, why can't I generate ANY boost when sitting idle and
~just revving ?
~