O290 to 150 hp

I’ve heard it mentioned an 0290 can be converted to 150 hp by swapping out the top end. Does anybody have the exact details on how this is done?

You're gonna love your RV three the way it flies good luck on your pre-buy

Divco

looked into that a few years ago when i was looking at another Pacer. It involves some case work but wasn't a big deal as I recall - give Divco a call, they can talk you thru it and let you know what all it entails.

I’ve got a 290 that has been bored to accept the 320 jugs. Another gent I know has also recently done this conversion.
If the crank is a “D” it’s the same as the 320.
If it’s an early or GPU they are flat tappet motors. And I’m not sure but I think the “D” is also. This is not a big deal if you are mechanically inclined. At each condition inspection you should check/adjust.
I’ve been told that a hot rodded 290 will make more power than the 320.
The 290 cylinders and piston rings are getting scarce or are expensive. Rings are $200 per cyl.
I wouldn’t hesitate to build it up as a 320.
Best,
Mark

150 H.P.

If your serious about the conversion I have a better idea. I have a 150 HP Conical Mount narrow deck crankcase that you could transfer your crank rods etc into. The previous posters mentioned the difficulty and extreme expense of 290 cylinders, pistons and rings. This would be an excellent project to pursue.
Lyc. 0-320 150 hp crankcase as removed $600.

Does anyone know if the mod described above (O290 case with O320 top end) can be done legally (via STC or other means) to a certificated plane. Pacer is one example that comes to mind. Interesting, hadn't heard of this one before. Thanks.

I had always heard when I had an O-290D on a Wag Cuby that you could fly cut the case for the O-320 Cylinders and get the thicker valves to eliminate ine of the O-290 issues- gulping thin valves.

The other issue is some say the camshaft was an odd length, almost too long, and flung oil toward the breather- so we all had air-oil separators. Maybe the oil migrated up the accessory case gears and made it to the breather.

If the cam lobe contact area on the lifters is wider on an O-320, I would lean that way.

I had no issues with keeping the dry tappets adjusted, just check/set at annual, added maybe 30 minutes.

You'll need a bigger carb to go to O-320 Cylinders, from a 3 series to 4 series.

Mahlon!?

Experimental only.

Don Pridham's Master's Thesis on Converting the GPU answers these questions. I never heard anything about a longer camshaft. I visited Don frequently during his authorship and went with him to John Thorp's shop in Burbank for a consultation on the conversion.

I have 2 GPUs, one converted by Posten of San Diego. One a Lycoming overhaul for the AirForce. The factory forgot to swege one valve seat and it came out on first test and was salvaged. I just had a new seat installed.

The only difficulty with Sodium valves is the expense.

FWIW