Experienced with Electronics, Electricity in general and many types of
engines large and small ( I race model aeroplanes !! )

I have always wanted to produce my own power and recent huge increases
in energy costs have prompted my to look at this again.

I have been trying for ages to come up with a good answer to the
following.

I would like to find an engine that produces a minimum of 20BHP (and
maybe up to 60)

It needs to be very quiet and economical.

(I can't afford the money, space, etc etc of a Lister CS by the way :( )

Fuel choices are recovered oils or possibly LPG / Propane ( I run an
LPG powered VW camper )