It is puzzling why the rule exists. Motorcycle engines aren't limited by the same problems that plague gas engines, namely fuel economy, emissions, or torque requirements.
Does anyone really believe that a 800cc car engine has a huge advantage over a 750cc roadrace engine? Right.
How about a 3000cc car engine vs. dual supercharged bottle-fed busa engines? OK.
The only thing I can think of is someone putting a Formula One engine in a motorcycle.
Guys with enough money to run F1 probably think LSR is a bit silly. Ever see a Marlboro sponsored LSR car?