Huge Engine

[Clear-&aMillion]

Flipping through the Cherokee handbook, it just hit me that what I thought was a "little" 4-cylinder engine actually has a displacement of almost 320CI!!! Hell, that's larger than some small-block Chevy V-8's!!! Sure enough, the bore is over 5" in diameter. Damn, its got coffee-cans for pistons! This was just a little surprising to me because I have a decent amount of automotive experience and you'd NEVER see a 4-cylinder car engine with that type of displacement. I guess AC engines are a different breed entirely. Now I feel like I have a "big" engine...

 

[GravityHater]

biggest commonly seen flat engine I know of is the continental 8-cylinder. I think its cid is around 720.

 

[USMCmech]

Big engines turning at low RPM producing a low amount of HP per CID at constant power settings. Sounds like a recipe for a long life and reliable engine.

Some of the big radials have cylinders with nearly a 1/2 gallon of displacement each.

My 4 clyinder 600 cc motorcycle engine OTOH has cylinders the size of baby food jars, turns at 12,000 RPM and puts out a high HP per displacement, add the fact that I am constanlty slamming power on and off.

Both the O-320 and my Motorcycle put out about 150HP. Care to guess which one I want to fly behind?

 

[erj-145mech]

biggest commonly seen flat engine I know of is the continental 8-cylinder. I think its cid is around 720.

The eight cylinder engine with a displacement of 720 cubes is a Lycoming IO-720. I've done some work on them, they're very accessable on the Commanche 400's and Pawnee Brave airframes.

 

[EagleRJ]

The maximum usable RPM of piston aircraft engines is limited by the propeller. You could probably make as much reliable horsepower with less displacement if you were able to go to 3000 or 4000 RPM, but the propeller would need to be too small to be effective (tips need to be kept subsonic). One work-around has been to add a reducing gearbox, but that adds weight and complexity.

I've always wondered how much horsepower an O-320 would make if you ran it on an engine dyno up to 5500 or 6000 RPM. Who knows if the magneto ignition would be able to keep up. You'd probably also have some serious valve float, as well as overheating issues.

 

[erj-145mech]

Thats why you throw a gearbox on the front, get that 3 grand down to a manageable 1800-1900 revs.