[scuzz]

what is the Big three?
I am going to put in a less restrictive filter, header and exhaust, if that is what you mean....

Why a 13 tooth? more low end tq? what if I go a 15 tooth one?that high end tq?

You guessed it!

13 tooth will help you if you do any technical climbs where you would have to crawl up or over something. For me it also put me in the "sweet spot" in the RPM range with grippy-horsepower robbing paddles.