Racing mower: pulley swap

So I have always been into mudding or crawling mowers but for my next build I wanna make a racing mower. I have no idea how to make it fast because I have not done a lot of trans axle work and I have only built mudding and crawling mowers so speed was not something I needed. If anyone has advice or some plans on how to do a pulley swap or something let me know!

Search around, there is alot of info on this topic.

Me and my dad built a fast lawn mower a couple years back just by doing a pully swap of a 4 or 5 inch pulley on the motor and a 2 inch pulley on the transaxle and i adjusted the governor a little to make the motor run a little faster and it would do 35mph on the road but the only problem was when i was off road and playing in mud the belt would slip witch wouldn't allow me to go fast off road. if there was a way to get the belt tighter it might work its just what we did you might be able to do the same and mess with it a little and see if you can get it to work better than we did i just never made it better do to wrecking it cause stock brakes suck.
good luck with the build I hope ya get it going it would be awesome to see it when its done.

What LMM said. Please use the search function.