<VV> Head Fins: How Smooth/Clean?

[Larry Forman]

At 12:53 PM 6/25/2005 -0400, N. Joseph Potts wrote:

>      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

Hi Joe,
My understanding is that you want the most surface area possible and best 
emisivity.  I would NOT polish them, since that actually reduces the 
surface area. You want them as rough as possible, so sand or bead blast 
them.  You are right to remove ALL the flashing possible. Tools that I use 
are a cheap hole saw for removing the thin webbing.  Next I use a 1/8-inch 
jobbers drill both 6 (or 8?) inches long and another 12 inches long.  The 
12-inch one is for getting close to the carb mounting pads.  Get several of 
the shorter ones, since they break easily.  I like to use them as a poor 
version of a side cutting mill so that they make up for the molds not being 
perfectly aligned.  You will likely notice that from top to bottom, there 
is usually an offset so that the lower fins partly obstruct the upper 
ones.  So chamfering the interface you essentially ensure an opening of 1/8 
inch width, regardless of any misalignment top to bottom mold lines.  A 
round cutting bit hack saw completes the work.  Just remove one of the end 
eyelets and hold either in the drill or with vice grips to remove more 
metal between the fins.  Make every molecule of air possible to get through.

As for cooling, I also use the Richard Finch approach and paint the outer 
1/2 of the push rod tubes to reduce heat transfer from the exhaust 
stacks.  You can also paint the exhaust stack part that is closest to the 
push rod tubes.  I also like to braze in washers in the exhaust push rod 
tubes at the head end.  This creates a higher level for the oil to flow 
down those tubes and thus the oil flows down the intake (cooler) 
tubes.  Braze in prior to painting the tubes.  I have found that I need to 
drill the hole in the washers so that the pushrod does not contact the 
inside edge of the washer.  I also need to grind the inside a little to the 
upward side, since the pushrod tends to ride in the upper part of the tube 
as the rod is pushed outward and the valve is depressed.  I scribe a mark 
on the washer indicating the upper oriented rotation of the tube.

Naturally, synthetic oil helps and removing lower shrouds helps too.  You 
might consider headers to remove all the exhaust log mass in the lower part 
and modify a couple of lower tin pieces to retain heater functioning.  This 
should help cool the engine just a little.  12 plate oil cooler and side 
A/C shrouds you likely already have in place.  I like a deep oil pan with 
added cooling and deep pickup.

This is a good starting place for cooler engines.

HTH,

Larry