Skip, both the SF and the earlier FSR are Schneurle ported strong running engines. However, the SF is a long stroke designed to run under 12,000rpm with props like 12x8 or 11x10. It is happiest around 11,750ish. The FSR is an over-bore revver that is best suited to use 11x7 to 11x7.5 props spinning above 13,000. Both engines do well with pipes.

David