So @pnora was correct back on page 1.Not sure I want to get involved in this fray, but the OP did not specify whether the racing fuel was leaded or not.
Back in the day, when I actually worked for Suncor (Canadian Sunoco), we did all of the different blends with pump unleaded, av gas and race gas. All were verified in the Waukeshaw knock engines in the lab. If the race fuel in question is unleaded, the straight ratio math formula can be used. If it is leaded race fuel, it is not that simple.