<VV> Head Fins: How Smooth/Clean?

[Roger Gault]

The "solid thermodynamic theory" (actually, heat transfer theory) says
smooth is better.  The rough surfaces trap air that doesn't move much.  Air
is an excellent insulator when it can't move.  That's what the fiberglass,
foam, etc. insulation in your house is doing - trapping air so it can't flow
much.  There's a point at which the flow becomes laminar, which won't cool
as well as turbulent flow, but I don't think we have to worry about laminar
flow around our heads.

My personal opinion on deflashing heads is that you should do it with long
1/8" drills.  You can get 6" ones at your local Home Depot, etc.  Use them
like an end mill to get in there and clean everything out.  The fins are
slightly tapered, so they're just under 1/8" apart in the center of the
heads.  The drill will open this area up nicely, which should improve
airflow.  Bob Helt claims to be able to do two heads without breaking a
drill bit.  I think he tells me this so I will feel bad.  It took me 7 to do
my last set.  But then, I'm not a patient man, and tend to cut sideways with
the drill, which bends it until it breaks.  A normal person should be able
to do it without breaking more than a few.  ;-)  If you like, I can send a
picture of the resulting head.

Roger Gault
Austin, TX


----- Original Message ----- 
From: "N. Joseph Potts" <pottsf at msn.com>
To: "Corvair List" <virtualvairs at skiblack.com>
Sent: Saturday, June 25, 2005 11:53 AM
Subject: <VV> Head Fins: How Smooth/Clean?


> I have a heat-challenged situation in my 66 Corsa 140hp that I like to run
> with stock distributor and ignition timing, and with stock shrouds. The
car
> is air conditioned, and that, too, is stock (A/C condenser is upstream in
> the path of the air that cools the engine). I live in a hot climate, but
at
> least I don't drive up long hills/mountains, and I don't pull a trailer.
If
> I use regular gas, I get ferocious ping. Premium gets me by with about
zero
> headroom on hot days.
>      I'm preparing a pair of (stock) heads for use in this situation, and
I
> have just "deflashed" them. Naturally, there remains a vestige of flashing
> at the narrow point of every through-passage, and I'm working on smoothing
> these down (not easy, as anyone who's tried it knows). I'm working on the
> understanding (not confirmed) that the closer I can get these flash
vestiges
> to disappearing, the better my heads will be cooled. And this exercise
> brings me to thoughts about the REST of the cooling fins that the cooling
> air passes over (the parts upstream and downstream of the point where the
> flashing is found).
>      Obviously, the cleaner these fins are, the better for cooling.
> Obviously, these fins get dirty in use (I'm tempted to spray coil-cleaning
> chemical into the ductwork of my assembled engine). But I'm still getting
> them as clean as possible so that at least they start off as effective as
> possible.
>      My real question is, should I bother to polish them (make them
smooth)?
> Could/should the FINISH of the fins have any effect on their cooling
> capacity, particularly after said fins have acquired a patina of dust
and/or
> (shudder) oil or grease? For the reasons described above, I need all the
> efficiency I can get.
>      If anyone has any actual experience to report from, or solid
> thermodynamic theory, I'd love to hear about it, preferably in a POST to
the
> list. Thanks.
>
> Joe Potts
> Miami, Florida USA
> 1966 Corsa coupe 140hp 4-speed with A/C
>
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