Re: Airbox Mod

[Luis Marques <marques@rtis.ray.com>]

Robert W Obrien <rwo@u.arizona.edu> wrote:
> then I reasoned: With CIS, on a long downhill, throttle closed,
> wouldn't this blow the metering flap to full rich (thus cooking the
> cat and blackening the exhaust, I'd think) when no fuel was actually
> required? Or does the decel fuel cutoff handle this eventuality?

The CIS flap will not rise any more just as it does not rise when you
are coasting at high speed without the "ram air".  The difference in
pressure is minimal.  Even then, the flap moves as a function of air
flow, not airbox pressure.  What happens is that with the throttle
closed, you end up with almost the same pressure before and after the
flap, so it raises just a bit corresponding to the little air the engine
is taking in.  The car won't run super-rich :)  As others have said,
cold air is much more important than an additional 0.1 psi of pressure.

If you let the intake air heat up from 80F (300K) to 120F (322K) due to
close proximity to the exhaust, the air mass going into the engine is
actually reduced by almost 7%!  That's 7% _less_ power thanks to making
a lot of holes in the airbox!  HTH

Luis Marques
'87 4kcsq