With the rules you posted here your going to end up with a motor turning around 6,000 rpms. The flywheel is the same flywheel that was on the early clones. With over 10 years of running HF motors we have not had a flywheel explosion, but when we were running the blue motors we did fling some magnets off of the flywheel and the motors were turning around 5,500 rpms and they have not changed the way the magnets are mounted. I will also tell you that a $130 claim will not keep most from spending another 45 bucks for a cam and valve springs and that will get the motors close to 6,000 rpms. A true hemi box stock motor will only turn around 5,300 and a non hemi will turn around 5,500 rpms. A non hemi motor will not run with a hemi motor with out being cheated up. About a half horse difference with the hemi being the better motor. As for the fuel tank. These motors run very hot and will have no problem lighting off raw fuel. When we had karts get up side down the fuel cap came of in most cases and dumped fuel. As for the stock muffler like I said the run very hot and after a few races they we breaking off on the race track and you just can't order new mufflers. Take a look at the rules on my track page under the notes section. They have been working very well for us. In a true box stock class you will have to tech hard or they will quickly get out of hand.