Several people have asked recently how to tell the difference between a steel-liner and ABC (ABN) FPs. It easy to tell by looking at the bypass side of the engine. The steel engine bypass sticks out like a bump on the intake side of the engine. The ABC version is smooth. The pictures below tell the difference. I think it is the same for all the different sizes of FP, I know it is true for the 15, 20, 25, 35, and 40.

   As I mentioned before, I only ran the 20FP-s ABC. I didn't run the steel 20 or 25FP. People tell me that it is fussier about fuel, as you would expect, but that it runs similarly. My steel 35FP ran pretty well but that was a very long time ago.

   And, because it was recently confused - no, I do not modify 20FPs for a "stunt run", because it doesn't need any modifications. The BBTU is a joke meaning to run it completely unmodified in all ways, including the stock muffler, head shims, venturi, spraybar, etc. NO changes.

    Brett

Or you could try to stick a strong magnet to the side if you have both in hand.

Brett's method works on eBay.

Does steel PC FP15 exist?
I have never seen a finned case FP15.

   I think that it does. I don't have one but I think I used one in the small engine experiments in the early 90's. But almost everything I did was with the ABC versions of the era, partially because that was all they made at the time, and partially because having to track down appropriate fuel was going to be a limiting factor. The intent was to come up with a system that you could get easily from Tower, Hobby People, or your local hobby shop and have it work in place of a Fox/McCoy 35 or 40FP. Chasing down all-castor or 22% blend was contra-indicated. The fact that the performance was astronomically better than a Fox 35 in almost all cases was icing on the cake.

   As always, now that the outstanding 25LA is also discontinued, the field is ripe for a repeat by someone else. Rules of the game:

   Use an available engine with minimal or no modifications
   Use a commonly available and inexpensive prop of around 4" of pitch. Relatively high in-flight RPM using low-pitched props are *why* it is so much better than a Fox.
   Run in a 2-stroke throughout
   Stays at a reasonable speed on a typical Fox 35-sized profile
   Make sure it will work on common fuel and with common available supplies
   Runs good on its side

    Brett

Hobby King has ASP engines that look good for a very reasonable price.  I have enough engines so someone else will have to do the test.  Or buy the engine for me???

Hobby King has ASP engines that look good for a very reasonable price.  I have enough engines so someone else will have to do the test.  Or buy the engine for me???

The ASP21 is a good running engine that seems to do well on the 2 planes I've had it on.  Right now it is on a Shoestring and I really like the way the engine speeds up as I go into stunts.