20. It never detonated, but we quickly determined that our Cleveland was supersensitive to timing changes on 91-octane pump fuel with as little as .5 degrees making a noticeable difference in the numbers. In the end, it was happiest with 27 degrees total. Amazingly, the new TFS carb was spot-on on for our testing and required absolutely no adjusting or jet changes to keep the air/fuel ratio in the 13.0 range through the pulls. That is literally the first time that has ever happened to us.