you need a minimum of 3/16 an inch. your going to have to cut the cowl. The motor will virbrate and tear it up as well and the high temps coming off the motor is going to make it worse. towerhobbies have flex exsions. Is it hitting on the bolt nex to the head or the one right on the muffler, if it right one the muffler the extension would alow you to rount the exuast to the bottom of the cowl and stick the tip of the muffler out the botom. I couldn't find any flex pipes though.