Intake temps and free power

[Joe Martin Cantrell <agiyo@domain.elided>]

Someone on the dim distant digest has quoted figures regarding our engines' 
power loss as the intake temperature rises.  As I recall, it was something 
like 1% power loss for every 10F degrees the intake mixture temperature 
rises, but someone out there will actually know.

Dean Cains wrote me directly today about underhood temperature measurements 
he and Tim Lentz conducted, almost exactly duplicating the temperatures I 
measured the same way.  Coincidentally, we did it on similar summer days, 
my temps in the 80'sF, theirs, about 90F.  Their cars are '74 Spiders, 
mine's the '72.

We put remote sensing thermometer bulbs in various places around the 
engine, and found roughly the following indications:

Engine compartment temperatures quickly climbed to 165F in their cars.  My 
thermometer would not read above 158F, but it reached that as soon as the 
engine approached thoroughly warm and stayed at that level at moderate 
cruising speeds.

Inside the SPICA boxes, same conditions, the temperature of a cruising car 
stayed very little above ambient!  So, although the engine was sitting in 
at least 160F heat, the air going into the injectors was well below 100F.

Sitting at a stop light or driving slowly, the SPICA boxes would heat soak 
and we saw temps inside them around 120-130F.  This happened surprisingly 
quickly, but they cooled quickly when the car got moving again.  I noted 
that driving over black asphalt warmed things considerably more quickly 
than traveling over light gray concrete, too.

I have bought a much higher reading thermometer, nominally for turkey, but 
really for repeating these tests.  Haven't gotten around to retesting yet, 
but I plan to do it in cool Oregon weather, to see how much difference 
there is if the outside isn't already 90F.  I'm hoping to do performance 
tests on a measured course, to see if there's anything noticeable, since 
the AROO guy with the g-meter doesn't think that will show anything.

I'm guessing that in cool weather, we may find more than 80F degree 
disparities between SPICA box and engine compartment temperatures at 
cruising speeds.  If I remembered that formula correctly, assuming about a 
130 hp engine, that's at least 10 hp difference...by using what the factory 
designed in the '60s.

Need I note that almost all aftermarket "performance" air filters breathe 
underhood air?  My Shankle Quadraflows are only for noise in the rare times 
it seems appropriate, or when I am fiddling with the SPICA settings and 
need quick access.  It's much easier to pull the front Quadraflow than a 
SPICA box.

Light colors reflect heat, dark colors absorb it.  I'm wondering whether it 
would be worth painting my air box white, insulating it, and perhaps using 
reflective tubing for the intake pipe to the radiator support.  The 
engineers among us probably know this off the tops of their heads.

I just checked the Spider's air box.  The nipples are there, but have 
vacuum line caps on them, just as the Berlina's will.  No rust, in 30 
Oregon years.  I wish I could say the same for the floors.

Cheers,
Joe
Portland, OR
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