A low compression reciprocating internal combustion piston engine with a prechamber in the head connected to a main combustion chamber in the piston, the prechamber having an igniter and a pilot fuel injector; the main chamber including a fuel injector and a ramp for mixing the prechamber gases with the gases being compressed in the cylinder. The engine is a hybrid having transitional combustion modes from spark-ignited stratified charge mode at low power, to a spark-assisted compression ignition at higher power loads, and a strictly compression ignition mode at maximum power loads.