I've tested 15% airplane fuel in a Force .12 (ofna LD3 ) and an XTM .247 (X-Terminator ) and while it "works" the power loss was quite apparent. (15% nitro and 18% oil...of which 12% is synthetic and 8% castor )

My theory is because of the increased oil content, and lower nitro and alcohol %, it retards the ignition point and has a slower rate of combustion. If you figure that a car engine is turning 30,000+ R.P.M. at times, there's not much time for the combustion process to take place, so at those r.p.m. the ignition point needs to be advanced, not retarded.
So...the added oil content will not actually cause damage to the engine (unless you lean it out too much in an attempt to "gain back" the performance ) but there will be a loss in power....

The main reasons you get more power with car fuel, is because of the generally higher 20-30% Nitro (itself an oxygen bearing compound ) and the increased % of alcohol allowed by the lower % of oil.

Those are JMO's...