I took one of my Italian made ST GS40's apart this weekend because it turns a bunch more r's in the air than my China made G40's. The sleeves are very different and everything else looks identical. The transfer ports and boost port in the sleeves are significantly different. The transfers are larger on the Italian and the there is a divider in the boost port on the Italian engine that is not there on the China jobs. They turn a 9X7 about the same on the ground but the Italian one will unload much more in the air. The Italian motor will wax my TT pro like it's junk but the China motors are pretty close if you get the right prop on it. With a 9X6 APC on both the TT wins but with some prop selection I was able to get them very close. Bottom line the prop that worked best on the TT didn't work well on the ST and vice-versa. TT 9X6 APC and ST 9X7 APC was very close. (Stock mufflers on all)