The American Predator drone uses a Rotax engine, which has:
* Electronic fuel injection (rare for aviation engines)
* Able to run on unleaded fuel
* Liquid cooled heads
* A gearbox to allow the engine to run faster than the propeller (propellers typically redline at about 2500rpm)

Rotax is the best selling engine maker in general aviation.

Interestingly, Alibaba has a Rotax ... knockoff (?):
https://www.alibaba.com/product-detail/QLY-912iS-Engine-Four-stroke-motor_1601062539068.html

Except it is priced identically to the real thing:
https://www.flyrotax.com/dis/rotechmotor/p/sales

I wonder if they're selling grey market engines to sanctioned countries...