A few things I copied and pasted:
Red Line recommends breaking in an engine on straight viscosity
oil.
Red Line does not recommend mixing race
oil with regular
oil.
Refining step 3: Add Detergents. Reacts with oxidized material. Helps keep piston rings clean (Rings are quite hot). Leaves an ash residue when combusted. Not used in airplane engine oils.
In an automobile engine, the piston speed (RPM) and therefore piston tempature changes greatly and quickly. The tempature differences allow the ash to break up into small deposits, and go into the exhaust or blow by the rings into the crankcase and lubricants.
In an airplane engine, the pistons are operating continuously at a single speed, and therefore do not go through heating and cooling cycles, so the ash deposits would not break up.
Generally, for automobile motor, lubricant is limited to 1% ash content. 2% ash is asking for trouble (although 2% may be okay for a diesel engine). Red Line Racing Oils are low detergent. Detergent is left out because ash can cause detonation.