Itinerant Air-Cooled

Many folks have deeply seated opinions re: engine building. Is it possible there are elements of truth to both sides? Here are a couple that have perplexed me.

Painting the case, cylinders, and heads. Assist with heat dissipation or hinder. And should that be black or white paint? And what kind? Or is it just a show car kinda thing.

And I just ran into a second. Polishing ports. There is a school of thought that says, yes, bright and shiny intake, exhaust ports and combustion chamber. Breathes easier, freer flowing, vroom. However, I've also heard no no no, you want the rough surface because it agitates and mixes the flow better vaporizing the fuel into the air for a cleaner burn, again, vroom.


I lean towards no paint, and unpolished ports. No paint because part of me thinks it would be insulative, unless it were the right kind, and black paint as white reflects heat. And a rough port combustion chamber surface rather than polished because my mind can wrap around a sensibility to the logic, and I'm lazy.


How do others feel? And I know there are other similar disagreements of method. FI/carb comes to mind.



neal

I'm a no paint voter. I understand that a thin coat of flat black on cylinder fins is supposed to run cooler. I still don't paint anything except the tin.

I'm inclined to believe that paint doesn't make a huge difference either way.
In the days of steam heating, test were done on cast iron radiators running at 215° F, and painted in a variety of colors, both flat and gloss.
The extreme spread of total heat put out (max. - min.) was only about 11%.

My understanding of porting on a carbureted or throttle body injected engine is that it can enhance top end horsepower--but at something of a cost of low RPM torque, as in starting out in first gear.
This is because of the low velocity fuel/air mixing that you mentioned.

regarding painting the cylinders, I would venture to say that the most important thing to worry about in keeping your engine cool over time is making sure it is leak free when you assemble it. Paint will do no good if there is a 1/4 inch of sludge on top of it. just my two 100ths of a dollar.

Polishing ports - I don't have enough experience to know. On my rebuild, I didn't do it.

Neal, if you have found that your bus is just not pulling cleanly from 5,000 rpm to 7,000 rpm off of turn 3 at the Laguna Seca track, you might want to port and polish.

Paint all of the tins and sheet metal bits beautifully, don't worry about the cylinder fins.
Colin

For FI engines, don't polish the (intake-ed) ports as you want the air to be disturbed as it grabs the fuel spray. Helps with the atomization.

Carbs (exhaust-ed) polishing helps at high rpms like Colin said..

Excellent. Always good to have confirmation that the logic based to arrive at a conclusion is sound, or at least shared.


neal

Thinned Rustoleum oil based flat black, applied in thin coats then baked in the oven are still like new after a year of use, which is noteworthy in our climate.