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"It is impossible for anyone to give you a resonable answer since we have no clue as to the year and model. Some year/models had marginal cooling and I would prefer to have those exhaust fins. Others never seemed to have a cooling problem."

Duane, I do apologize for excluding the vital information, if you please: 1977 R100/7, running TM 38 Mikuni carburetors, lightened flywheel, balanced clutch, con rods and 9.5-1 pistons, omega ignition, 38mm exhaust, drilled clam shell air box with 40mm tubes to carburetors. I don't know if any of this increases heat but I mention it just in case. I am running an oil cooler, omega electronic ignition and solid state voltage regulator, blue coils and ngk wires. The engine is more like a S but for the valves. When I built the engine, my engineer friend convinced me that the smaller valves would work better than large valves. So far, I can't complain.

Ah yes Major, didn't think 'bout that.
Now that I have thought about it (briefly) wouldn't the star nut transfer heat from the header to the head, or would there be sufficient contact between header and head to negate my theory?

ME 109 wrote:Ah yes Major, didn't think 'bout that.
Now that I have thought about it (briefly) wouldn't the star nut transfer heat from the header to the head, or would there be sufficient contact between header and head to negate my theory?

Dunno, but I certainly can't think of a reason why it would transfer a different amount than a non-finned nut, except that the finned one would dissipate more of that heat into the air.

The star nut is transferring heat to the air, not from the header to the head. Given it's location, the header is the primary source of the heat, not the head itself, which has its own cooling fins. In other words, if there was a heat differential it would be from the header, to the exhaust port, to star nut. Sorry if I'm pointing out the obvious...

Yes Tim, I was thinking of 'other' heat transfers besides the obvious transfer to air.

BTW, I just received a seat for my RS from Germany which was somewhat delayed.
Mail tracking showed it was somehow diverted to Honolulu.
Anything to add?

Well... you do know what DHL stands for, don't you: Delivery Halfway Lost, or maybe it's: Deliberate Hawaiian Layover? (jest sayin')

If the exhaust nuts are cooling the header pipe rather than the head then except for the cosmetic reason of limiting bluing, cooling the exhaust pipe is not necessarily desirable. I thought there was some beneficial effect on gas flow that results from keeping the exhaust gases hot.

Modern bikes don't have them do they. Is that just a fashion thing or because they are water cooled ? Do Airheads have them because they were fashionable at the time ?

"If the exhaust nuts are cooling the header pipe rather than the head then except for the cosmetic reason of limiting bluing, cooling the exhaust pipe is not necessarily desirable. I thought there was some beneficial effect on gas flow that results from keeping the exhaust gases hot.

Modern bikes don't have them do they. Is that just a fashion thing or because they are water cooled ? Do Airheads have them because they were fashionable at the time ?"

That's the question I had in mind. Are the nuts merely cosmetic or do they provide a function?

That they dissipate heat is a given, on an aircooled engine, a plus.. no? They sure are pretty, too! Seriously though, I don't think there is any real benefit at highway speeds, but if we take it to the other extreme, when your slogging through hot sand for hours in the Paris Dakar, or stuck in traffic on a hot afternoon... that's when the benefit kicks in. What do you think?

Almost no modern bikes are purely air-cooled except for some low performance small bikes. Pretty much all the current "air-cooled" engines have a oil-cooler and some sort of oil cooling of the exhaust seat area. I know the Ducs and BMW's are, and I think even Harley has gone that way, but they also have a much lower HP per cc design.