Re: More hot air

[bearbvd@domain.elided (Greg Hermann)]

>On this, I think my point's been missed. My question of the free lunch was
>not about the rest of us obtaining free knowledge from someone else's
>study; no, it was about the reality of obtaining say 13 per cent HP
>increase in a standard Alfa motor when changing from hot to cold air
>intake.  That particular lunch really would be about as free as they get.
>But don't get me wrong here..... I haven't been saying that it doesn't
>happen; I've just been asking for some evidence. (Asking for evidence must
>be due to some strange ideas they instilled into us when we did our
>engineering degrees :-)
>
OK--There is no free lunch involved in using cold air intake. The amount of
oxygen breathed in by the engine (and therefore the amount of fuel that can
be burned and the power produced )  is ROUGHLY proportional to the density
of the air breathed in by the engine. I say ROUGHLY because slightly denser
air encounters slighter higher pressure losses in flowing through the
intake tract (pressure loss in a fluid flow at a constant velocity is
proportional to the density of the fluid).

So--the power produced by an engine operating under a given static air
intake pressure is ROUGHLY proportional to the reciprocal of the ABSOLUTE
temperature of the intake air.

This DOES NOT address the fact that there may be some "RAM AIR" effect due
to forward motion of the vehicle and the location of the air intake. RAM
AIR effect simply takes advantage of what is called the "stagnation
pressure" of the air stream around the car. The pressure increase in the
intake air (above ambient atmospheric pressure) is proportional to the
SQUARE of the speed of the air flow over the car if the intake scoop is
well placed.

Greg

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