In my opinion, it's a waste of money anyhow.
When we were young and didnt know any better, we ran Briggs singles. They were always 28ci.
Won many, many races with them against 31's and 33's.
We went to Oskaloosa Iowa years ago for a race. Started somewhere aound 12 mowers. My Brother in Law and I finished 1-2, and lapped everyone else at least once. After the race, I was asked what we had for engines. I told them exactly what it was, and they simply looked at me like I was a liar and walked away. There wasa video of that race on youtube. Don't know if it's still there or not.