Q: What’s the reason the O-320 E series can’t be converted to a higher compression?
A: It’s been a long time since I’ve had this question come up, but the answer is easy and may not be to your liking.
The following O-320-E series Lycoming engines may not be converted to high compression because these engines are built using “thin wall” main bearings: O-320-E2D, E2G, E2H, E3D, and E3H.
Other than those, some models may be converted to a higher compression, however there are some caveats.
Of course the pistons, piston pins, piston rings, and exhaust valves must be changed, but most low compression engines have plain steel cylinder barrels and the high compression engines must have either nitride or porous chrome barrels.
This begs the question: Even if you had a model that was acceptable to convert, would the expense be worth the cost just to gain 10 horsepower?
One suggestion I might mention is that if your engine is high time, but all operating parameters are still within specs, possibly just completing a top overhaul would provide you with some additional horsepower you’re looking for.