What you're talking about sounds similar to what's called a tongue muffler. I couldn't find a decent picture to attach so here's a link to one. http://www.brodak.com/shop_productde...ProductID=6687

However, these are only used on CL engines which are never run at full power so any possible power loss isn't a problem. They're still a bit on the noisy side though compared to a proper muffler, just much lighter.