Tim, I discovered the Diesel/gas mixture as a method of increasing the octane rating a bit on the low-compression race engines we were forced to run as a cost-cutting feature of the race association at the Nashville Fairgrounds track. The "super-Stock" class dictated a compression ratio of no more than 9:1 mostly as a hedge against the very radical engine builds the deep-pocket sponsors could afford. Then the track officials, in their infinite wisdom, decided to make all of us buy the 102 octane gas the track sold, which was intended for 12:1 compression engines. It burned WAY too slow to run right in the lower compression engines. We discovered that a mix of plain old pump premium gasoline with 5% Diesel mixed in had the right burn rate for best performance. Adding a slower-burning fuel such as Diesel actually raises the octane rating slightly due to increasing the specific gravity (and slowing down the burn) of gasoline. 87 Octane regular gas is the fastest-burning grade. By slowing down the burn, the octane rating increases and the anti-knock tendencies improve. Diesel fuel also has more BTU's per gallon than gasoline. At one time, I had a huge number of dyno test data sheets to document the power increases and the ability to run more ignition timing advance with the Diesel-mix gasoline but those went away when an assistant principal at the school where I taught decided to trash some "old" files from my shop storage area!
One problem was duplicating the color of the blue dye the track added to the gas they sold so they could take a sample from our cars and fine us for using gasoline not purchased from the track. I found that adding a little machinists' DYKEM layout blue made it exactly the right color!
Jerry
