The recommended engine is the OS 1.20 FS. That's what I'm putting in mine. But if you want more power, I'd find the weight of the OS 1.20 and then shop for more displacement at the same or less weight . Be very careful not to bolt too much more weight onto the firewall and then add lead to the tail to get it to balance! Your wing loading will shoot up quickly and then you will have a very fast, poor flying airplane. The wing loading is already very high on the Gee Bee assembled as stock.

Yak