hey i got a almost stock z250, i got 18 inch tires and a twin air filter, what kind of gains would i get with the yoshi rs3 slip on, i read that you could get 6 horsepower with it but i didnt know if that was stock or with other mods, also, is the big gun evo x exhaust muffler stainless steel. i like to ride track a lot, some trails, and i love to jump and do wheelies, thankyou