The Jett 40 as delivered is a high power, high rpm engine. OS VF 40's, which are also engines designed to run in the high rpm manner, have been used with success with tuned pipe exhausts. Mac mufflers produces a line of mini-pipe one piece muffler systems that seem to work like bigger pipes when attached to medium rpm engines such as the OS FP series. Yes, I do I believe that Richard Oliver does sell a pipe setup of the RO-Jett.

Pipe setups get complicated. They are expensive, and the ones used for CL are comparatively short-lived, especially at the relatively expensive cost of each such pipe.

Medium rpm engines can sometimes be successfully used for CL aerobatics with the same carbon fiber props used with piped setups. In this case, the engines are allowed to run at comparatively fast speeds, while the props have low pitch setting to keep the speed of the plane in a reasonable zone.