www.abellrc.com or www.bennettbuilt.com both have mufflers as described above. They are exhaust diverters, and DO offer free flowing performance over most any other in cowl solution. My only warning is that they are '''loud'''. Our club doesn't have noise restrictions, and we had three of these mufflers on 26's in our club, and the last of us changed to something else because of too many complaints. Between the two mentioned, I would recommend the Abell, my post is only to warn you of the noise, if that is of any concern where you fly.

As Karol said above, the Toni Clark or Macs products exhausts are going to be the best performing, and cost you accordingly. The Abell and Bennett will be smallest, lightest, and perform well, but loud. The happy medium regarding price, sound and performance would be a wrap around pitts style from any of the makers listed above.

Chad