Re: More hot air

[Simon Favre <simon@domain.elided>]

Aside from all the denser air and other points, there is a general rule
for any engine that operates by letting heated gases expand to do work.
Thermodynamics says that any such engine will operate more efficiently
(meaning more output for a given input) with a greater temperature
differential across the engine. That means the same engine with a cooler
intake and/or a hotter exhaust will produce more HP. Given a fairly
constant combustion temperature determined by the A/F ratio and type of
fuel, the exhaust temp is not as much of a variable. If exhaust temp
gets too hot, the engine is not tuned properly and will likely grenade.
In addition to the LED A/F ratio meters, you can also fit an exhaust temp
sensor to a car you're trying to tune to the max. So for a given optimum
exhaust gas temp, the incoming air temp can be significant purely due to
thermodynamic efficiency. I know, I know, most of the EE's in the audience
(me included) scratched Thermodynamics off the curriculum. ;=)

The trouble with car engines is that there are so many variables involved
that it's tough to predict exactly what the effect of a particular change
will be. The thing about intercoolers is not only the cooler intake charge,
but that it allows the FI system to cram more fuel in with the denser air,
thereby producing more power from burning more fuel. Intercoolers also
allow higher boost pressures without detonation, again creating more power.

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