My Formula S is almost finished, looks like it will be in the low 50's.  I have a Barker Magnum 36 I planned to use, will it handle this weight? 

  I don't know. I do know that this is *no problem* for a stock engine.

   Brett

If you run the stock Magnum in the Formula S, then I could highly recommend the Thunder Tiger Cyclone 11 x 4.5. While I'm running an OS .46LA muffler on mine (with .272" venturi, Thunderbolt idle bar and 10-22 fuel), I have another one in an Olympic (Monty Summach's old Oly) with a Randy Aero tube muffler...engine/muffler seems fine, but only a few tanks through it. Usually, a "tuned" engine will require more pitch. The 10.5 x 4.5 APC might still be useful, and don't forget that you can repitch APC's and such.  Steve