I think my ST .45 was the S with the old type noisy muffler. I don't have one of the new ones. The Picco does not need any more breaking in. It looks well used, but good shape. I have a couple smaller newer Piccos, and the .12 is much better than any .15 I have. On a Supertiger .40 and many others, I often fill the front radius with solder especially when it looks like it has been drilled too deep. I also grind a bit on the window to smooth things out a bit. I have not measured more than 300 rpm on anything, but normally do it if I have the motor apart that far. I think I will start to widen the exit hole to the sides like a Fora does. I am not convinced the "turbo" cuts at whatever angle, is the way to go. Just a bit wider to get the air around the rod and give the impression of a bigger crank hole. I noticed a pic of a Jett crank which has pretty much a cut straight across the centre of the back face of the crank. I guess that is to direct it to the ports, maybe it was on a rear exh.? I have not got a new chinese ST, but do believe them when they say that they have not changed much. I think the ring is maybe a couple thou. different, and the cat's eye cutter got a bit dull, and pushed up a burr. The operator likely got reamed out for that and smartened up. Too bad no one wants to carry the ST brand any more. I guess there is more money to be made on a million drones than with us old farts toys.