I'm using the stock muffler, which from the side view is hardly noticeable, you can see it barely from the front but underneath the plane you can see the whole thing..., it's not really that bad and if you don't want to spring for a pitts muffler the stock one is mostly hidden excpet from the bottom view. (see photo below) The secret to keeping the cowl from cracking is to keep all your cuts into the cowl rounded at the corners... no jagged cuts or square cuts... that's where the crack will start.. I just used a dremel for the whole process.. oh and fit the mounting blocks well, sand them to match the contour of the cowl... so far i've got about 40 flights on her and the cowl is still ok... knock on wood....