Hi All:

          Are fins on the cylinder head necessary? I have engines with none, with only half of the head covered with fins and heads with no fins. I was informed that a Stunt engine must have fins to run well.  This seems counter intuitive as the Stunt engine may run the coolest of all engines.

          Thoughts/comments?

                                                                                 Be safe and be well,

                                                                                  Frank McCune

YES the fins  are  NEEDED  and  are a  good thing, many engines  ruined by people milling the fins off, It is  easy to make them hotter, HARD to cool down without  fins, You can also make more stable power with fins

Randy

   Does anyone have an idea why the HP  .40 Silverstar has no fins? 
      Always wondered , John L.

   Does anyone have an idea why the HP  .40 Silverstar has no fins? 
      Always wondered , John L.

Dear John, Mr. Paul Bugl was one of the really most talented engine designers. (Sorrowfully he passed 'round his early fifties. ) He really did know, what he was doing. 
Well, I used HP 40's from 1983 up till 1999,  and one model of mine still exist with HP.
As HP forties was made originally for R/C, I made some mods, as follows:
-sleeve lower by 0.8 ÷ 1.0 mm
-inlet closed from 190-200°s to 170° (only by Gold Cup: Silver Star was not so extremely open)
-we used the black plain cylinderhead, or machined off the fins of GC head's fins...
-and I collected the original nozzle-type carburettor from the oldschool friends, who stubbornly bound theirself to the spraybar-version.
Our engines were absolutely in contest with the ST-46. We used 12x4 Tornado or 12x6 Modela (wide wood) props mostly.
Istvan

The HP Gold Cup 40 had fins. Didn't they come out before the Silver series?

A billet aluminum head is quite adequate to absorb and dissipate heat. Cooling fins just make it look more like an engine. Look at the Fox 35, do you think those little nubs on top really do much?


Motorman

NOT in stunt, where  people want to cycle  quickly, R/C  or  racing  where your running a constant 2 cycle, is quite different than Stunt runs, I made deep fin heads for the FOX 35 back in the  1970s, They works much better, and the FOX 35 would cycle faster , you could get more power out of it, and slow returns from LEAN was improved, When I designed the Smith Fox hemi head, that is the reason it has more fins  and  deeper fins, Most of them also had extra cooling fins around the circumference , These work better, a lot better.  AS I wrote earlier, I also test much the same on many other engines, More area to dispel heat, IS  almost 99 % of the time  better.  Shaving  the fins  off  is  mostly 99% worse !

Randy

Oh hell NO !  WAY TOO MANY FINS , you get right back on those machines and  trim  all the fins  off that motor !!!

    I have a file right here, let me take care of that for you...

    Brett