Re: More hot air

["Hyndes, Keith" <KHYNDES@domain.elided>]

It was written:

>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

The 13% increase or so is on the mark if comparing a turbo charged
non-intercooled engine, with an intercooled turbo engine. When Saab
introduced intercooler on the 900, they went from 145 to 175 HP, albeit with
an extra 8 valves (which don't make anything like the difference they do in
a NA engine). 

The air to air intercooler will typically shed 30 degrees C (54 F) from the
inlet temperature in the turbo engine, the issue being that the turbo heats
the air up considerably. It is essentially similar to a radiator.

>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.

In that case the difference between 20 degree C and 40 degree C (68 and 104
degrees F) would be approximately 7 %.
Large diesel manufacturers publish graphs, ie BHP vs. temperature and
altitude.

Cheers
Keith

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