I have more of a theoretical question about exhaust and intakes for the crf50 (2004, 2006) and xr70s (2002). Right now they are all stock and will remain that way for some time, but as my boys grow, I plan on potentially mod'ing them a bit. One thing I noticed about the 50's in particular is the somewhat lack of exhaust options - I know there are several mfgs out there, but I was surprised to see not too many mufflers only - just full exhausts. It appears the same can be said for the 70. I've done some reading and it appears an exhaust and intake on otherwise stock bike doesn't get you much gain - I'd need to look at engine work and bigger carbs - this true? I was also surprised to see that really the only exhaust mod's out there are removal of the arrestor and/or the end cap. I did see some mufflers on amazon, but I'm guess they are just cheap chinese mufflers that may look cool but thats about it? I was maybe hoping to see a name brand muffler only - or is all the HP gains with these in the head pipes?