Wow.. apologies, I totally missed this post in here! Looks like it was moved in.
You got some good information.
In general, the performance of the Sport Jett side exhaust engines and the FIRE-JETT rear exhaust engines is identical. The difference comes from the full sized tuned pipe giving you a bit more power increase, but more importantly you can set up the long pipe for exactly the prop, rpm and application you are working with.
For instance, on a FIRE 50, it can be set up tuned for turn a 9x7 type prop at 19,000 rpm or alternately swing a 12x4 prop at 13,000 rpm. It all depends on the pipe, pipe length, and what your expectations are.
Folks use the FIRE engines on speed planes, diamond dusts -- but also on pattern aircraft -- and also a lot of the SAE heavy lift college teams use the engines set up for big props.
Having said all of that, for 90% of sport plane use -- the standard Sport-Jett side exhaust engines with the Jett-Stream tuned muffler will provide outstanding performance in a variety of applications.
I hope this is helpful, and again I apologize for the delay.
Bob Brassell