RE: Intake temps and free power

["Ian Lomax" <sfalfisto@domain.elided>]

Well let's see how much I remember about my thermodynamics course.

1.  Heat can't flow for a cooler to a hotter.  Ok, actually that's from
one of my dad's British comedy albums...

Seriously, there are three types of heat transfer.  Conduction,
convection and radiation.  The color of the intake is really only going
to affect radiation, and I suspect that most of the heat in the engine
compartment is from convection (the engine heats the surrounding air,
which then heats the intake box).  I bet you'll see a lower temperature
with a chrome airbox, but I doubt it's much, and will eventually be
offset by the convection effects.  I have a box painted black if you
want to do a back to back comparison someday, when both our spiders are
in the same state. :-)

On the subject of aftermarket filters and "cone" filters, they might
show a power improvement on a dyno, but it's probably because it's
pretty hard to get good airflow on a dyno, even with a big honkin fan.
If both airboxes are sucking hot air, the cone might be better.  But
I'll stick with my stock airbox.  Besides, without it the car is damn
loud, too loud for my taste.

Let us know what you find Joe!

Cheers,
Ian Lomax

> -----Original Message-----
> From: owner-alfa@domain.elided [mailto:owner-alfa@domain.elided] On 
> Behalf Of Joe Martin Cantrell
> Sent: Monday, February 03, 2003 9:03 PM
> To: alfa-digest@domain.elided
> Cc: John Hertzman
> Subject: Intake temps and free power
> 
> 
> 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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