i noticed that most of the good profile flyers have mousse cans. how do they help?

I have never actually used one , but my understanding is they increase the rpm's of the engine and also weigh a little less.

I made one for a OS 46 VF rear exhaust once and really tourned on. 21000 rpm on a 10x7 prop.
A sreamer. Had it on a sweet stick. The fastest stick at the field
Not exactly sure how it works but I think it actually makes the engine think its running a lower rmp than it really is and gets fast. It was described to me in lamons terms like this so I am not exactly clear. BUT IT WORKS...

Shane

Mousse Can Pipes and expen$ive tuned pipes deliver very similar top end power boosts. But the throttling characteristics of a MCP are vastly superior to the expen$ive tuned pipes. A MCP gives an engine a very linear throttle response all the way from a tick-over idle up to full power. In fact, the throttle response with a MCP is usually even better than with the stock muffler. But an engine with a tuned pipe will experience sudden and drastic RPM changes as the throttle is slowly opened and closed as the engine gets "on the pipe" and falls "off the pipe". These sudden and drastic RPM changes make it very difficult to precisely and accurately control the propeller thrust, especially when hovering.

The MCP works great in fun fly planes because of the power boost it delivers, and the improved throttling characteristics.

Mouse cans have been explained to me as a high pressure fuel delivery boost that atomizes fuel better. The varied bolt on performance boost across a wide range of engines seems to be contradictary to if allot of exhaust tuning is being done.

I dont really know or care but they are lighter and perform equally to the stock Jett tuned mufflers on my (4) Jett30's I use in combat.