Hi WM;
The web site is
www.abellrc.com, go to accessiries then to mufflers.
They use to have pics of there mufflers but they don't come up on my computer. The one I have is pretty basic, (2 1/4" x 2" x1") with a straight stack. I would give them a call just to confirm. It increased my rpm by about 800-900. Certainly don't need it in the air but has been great for water take off.
I didn't want to "horse" the model off the water but the added rpm gives me extra power if needed especially in calm water conditions.
A little noisier which may be a consideration where you fly.
Regards
cgcrc