You'll be hard pressed to find help on here to just make your home mower go fast.This is a racing forum that supports sanctioned racing.
However, maybe with a little information about yourself and where your located we can put you in contact with someone from your area for you to join with.Different organizations will have different build rules so as sr71mopar said, it's most important to get with a organization first.
We are always looking for mow-er racers!