Re: More hot air

["Rich Wagner" <drsavage@domain.elided>]

Hi All,

Graham wrote, referring to my previous post where I showed the power drop
associated with different induction temperatures:

>I wonder Rich, were these figures merely by way of general 
>example, or might that order of change be really expected in practice on a
>2L Alfa motor?

Those weren't just general examples.  To come up with those figures, I used
an engine simulation that I wrote some time ago.  The first figure, 129 HP,
was for 2 liters of displacement, compression ratio of 9.0, wide open
throttle at sea level and 72F, and peak power at 5,700 RPM.  The second
figure, 114 HP, was for the same specs, except for a temperature of 110F.


>Naturally I've tried restoring the 
>rammed cold air input to the engines, but can't say I've ever noticed a 
>lot of improvement..... well to be really honest, can't say I've noticed 
>any..!!    Maybe one needs a dyno test to tell...... but I was hoping for 
>something more significant.

Unfortunately, I don't have any actual test data that I can show you. 
There is, however, an analogous situation in the aircraft world. 
Carbureted airplanes carry "carburetor heat" systems that take the
induction air and route it through a cuff surrounding the exhaust before it
enters the carb.  The purpose is to melt any ice which may have accumulated
in the venturi of the carb.  When the switch is thrown from the cold,
unheated position, to the heated position, there is a large RPM drop.  Part
of this is caused by enrichment of the mixture due to the less dense air. 
However, even after the mixture is readjusted to peak, there is often a
multi-hundred RPM drop, and indicates that the engine is generating a great
deal less power.


Rich Wagner
Montrose, CO
'82 GTV6 Balocco

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