I'm going to do the boring old fart bit here! you're 16! being on the road is a privilege! the law says you can only ride a 50cc that will only do 30mph! somebody at the manufacturers spent months on a computer designing the exhaust to give the best performance, sound, weight etc etc to meet those criteria! do you really think you can improve it with a hacksaw/welder? all you will achieve is a badly running, loud, annoying!, death trap that, if you're really lucky will go 5 mph faster but will probably seize after an hour! get another standard exhaust, put it back on, ride bike as intended till you're 17, then go through the system to progress safely onto bigger faster stuff! I know this isn't what you wanted to hear but it's all you'll get from me, sorry!