The B11 Piston and sleeve will work just fine with the F11 case and crank. Altho the performance will not be as good as you are used to from the F11. The B11 sleeve has a much smaller exhaust port and less aggressive timing. It should run faster than a standard B11 as the F11's crank is more aggressive. If it's something you already have and want to try it out to see how you like it you will be fine, and might find you really like the power-band. Last year I tried the F11 crank in my B11 and really liked it!!! If your curious because you want a replacement for the future I would stick with a F11 P/S.