Re: WOW!!! what a difference a little grinding can make.
The "notch" is on the bottom intake side of piston. This makes the intake port about 15% greater by area when the piston is at t.d.c. I had about 50 miles on the motor then I had to fully disassemble it because I had a foreign piece of debris jam up the crank and clutch gear. I didn't want to touch the piston initially. I ported and polished and gasket matched the top end but I left the piston stock for the break in. I had it all apart because of the Little jam up with the gears and lost my patience and said the heck with it I'm going to cut the piston now. I noticed the difference in power the first time I got back into the gas going around a corner. The throttle response is significantly better as well but if I had to guess I probably increase my low end torque by 8 to 12%. You don't have to remove too much just remove your intake bring the piston to top dead center and you can see that the piston skirt reduces the area of the intake opening.