It is 32.9 decimeter square dm^2 that is equivalent to approximately 510 sq.in.

It looks like the spinner size is incorrectly shown in the manual page 2. if it is a 57mm, it is 2.25". Well, I am going to have to call the Tru-Turn & Kyosho again.
I had to dremel out the 2.25" TT standard spinner to use the YS engine. Otherwise, Ultimate spinner is necessary to use Tru Turn spinner/adapter.

Erdel,
there isn't much of power gain on 4-stroke using a larger muffler (my YS 91AC gained about 100 rpm using ES carbon muffler for 120). Also, no manufacturers call them as tuned pipe. They are called just muffler. Benefit of the larger muffler is the quietness. None of my YS 4-stroke use the standard muffler that YS provided. However, I tried YS 53, 63, 91AC & FZ, 140L etc with stock muffler. Then used Asano, ES design, Bluebird, Hatori, etc mufflers to reduce the noise.

Anyway, I will probably have the Oxalys in stock next week.

Ihncheol Park
P & A Hobbies