Power Generator

Question1>SIngle piston 6.5kw generator will consume +- 20litres of fuel in 12-14 hours or about 22 pounds (10kg up to 18-20hours 1kg lpg=2liters) lpg at just about full load 14amps at 220volts.WHat is the mechanical output of the engine (kwatts and or hp)and at what Rpm should engine turn to output 50/60 hz.?

Question2>a 4 cylinder engine at Idle refs 1000 - 1500rpm the output should be+- 12kw it should be more fuel efficient.?Seeing that i run on lpg the efficiency is higher and more cost effective.I also use the enginge cooling system and the exhaust system to heat up the water for in house consumption.The engine has a gearbox but i cant say what the ratio is.WIll this engine be as fuel efficient as the 1 cylinder engine.?

Thanx
MAx