Onan Engine Info


Well-Known Member
Supporting Member
Jan 4, 2007
I know there have been some Onan engines used on ultralights. By the little info I've found it appears that a stripped-down, ready to go on an airplane 20 HP engine might weigh as little as 77 Lbs.. Some specs show pretty high weights which I think might be all the shrouding etc. but did some Onan engines have cast iron blocks and others aluminum? Also, in my searching it seems that many different Onan engines of varying HP share the same bore and stroke. I wonder if the HP rating is because of a smaller carb, reduced compression ratio, different cam, or ??

If anyone has knowledge of the Onan horizontally opposed twin cylinder engine I'd appreciate it if you'd shed some light on what might be acceptable or unacceptable as a potential Onan engine for an ultralight.

FWIW....a 1/2 VW of just higher weight is no doubt capable of more HP, but if there is a 77# (or less) Onan out there, the lower HP might be able to useable for what I have in mind. There are always a few things to be done to engines to increase HP. I know there's "no replacement for displacement", but some mods can bump HP without compromising durability.