Here in Canada we have 2 engines we use in 426, Q500 racing. We essentially fly by the AMA rules for 426, with the exception we allow using a Nelson SS Q500 engine with the mini pipe inside the muffler removed. The result is a detuned Nelson SS Q500 engine.

The JETT engine and the Nelson run side by side in our races with no noticeable speed advantage to either.

If you are looking for an engine to practice with why not get a second hand Q500 Nelson, Aero sells the mufflers with mini-pipe removed. These engines are operating below their design and last forever, and in the long run will probably be cheaper.

The downside is they are probably faster than the engines allowed in your area, but practicing with a faster airplane will only put you further ahead of the crowd in a real race.

.... just a thought