The shoulder is not an issue. There's plenty of clearance. That is good thinking though. Today was my first day competing with my .21 in my Losi 8 buggy. I've owned most of the major manufactures and this engine is the best of everything. I've got power that is more than enough, nine minutes of runtime in my main, and it's easy to tune. Using the os p3 and the Jammin' JP3 pipe. Also have a 6.5 carb restrictor in it now. Trying to make it easier to drive and going to the best runtime I can get. It's still very tight and I'm getting nine minutes. A few more race days should improve my runtime even more. My temp is 185 consistantly. Can't wait to get the GRP pipe in a couple weeks.