John, I have several gas engines of the conversion variety but have no broad experience to elaborate much on them. I have custom mufflers on all of them but do not consider that they are anything tuned. They have more of a exhaust diverter.

There are a few guys at the field with the 3W 150 type engines and I've never talked with them about cans but I thought they had what was considered to be the can variety of mufflers on them?

Now this is just my opinion from watching and listening to these "big guys" but I considered the cans to be more in the tuned muffler department. These engines, however, are never run WOT except for 2 or 3 seconds at a time.

Enjoy,

Jim