Does anyone have experience with the Air Plains 252hp upgrade to the O470-U on a 180? I would also be interested to see a copy of the installation instructions. John Jewell has the identical STC for the 182. I have a 180 with the 204 prop and its not ready for an engine overhaul but it does need a carb overhaul. Add a bigger crossover and a new prop governor and I get a HP bump. Something to consider?

Prop needs low pitch stop changed and carb needs to change to 4-5 6050 model . In Canada I know of a few 0-470 r and s models had u cylinders in stalled on engines does same thing

Sounds like they just turn the rpm up on the 470U engine from 2400 to what, maybe 2600?
So a high compression 470.
Sounds similar to the Norland conversion, IO470 converted to carb-
just a different route to get there.
Too bad no one supports a simple high compression piston mod to a standard 470, K thru R model,
that could be accomplished with just a top overhaul.

I'm curious what's gonna happen with high compression and/or IO engines when 100LL is phased out--
which we seem to be in the beginning stages of.
Are they / will they be approved for use with whatever the latest whizbang unleaded avgas is?
I'm an mogas guy with a low compression engine, so I have to admit I haven't been tracking this issue all that close.

GAMI’s G100UL will work in all these engines. They are in the process of getting STC’s for all piston aircraft.

Continental derated the O470-U by lowering the maximum RPM to 2400. Bonaire developed a 22hp upgrade STC for this engine by runnig at 2625 RPMs on the 182. The STC data was easy to acquire for the 180 at the same time so Bonnaire applied for both airframes. In the late 90's, John Jewell bought the rights to the 182 side of the STC and AirPlains bought the 180 rights to the STC. The STC allows the O470-U w/204 prop to run at higher RPMs by opening up the carb (better breathing and fuel flow), increasing the crossover tube size (from the 520), resetting the prop stops, and changing the prop governor (and a tach setting, of course). This is what I've been able to discover so far. I haven't any hands on experience and would really like to see the instalation paperwork and talk with someone who has flow this mod. I don't know what more is involved and what the restrctions are?
I do know the MA4-5 part number is 10-6050. Marvel Schebler has one on the shelf ready for swap out with mine. I'm looking for a prop shop and the pricing on the prop governor and a cross-over tube.
Does anyone have the installation instructions? I'll do a little more research then give the folks at AirPlains a call. I've heard nothing but very good things about them.

I'd say go for it. I've flown a 55 180 with a high compression 470 and it was a hot rod. If you are staying carbureted, and don't want to shell out for a O-520, this is a great option. I've even heard anecdotal stories of a high compression 470 outrunning a low compression O520 at altitude (10K+). Do some digging on compression ratios vs altitude, I believe it.

The downsides to a high compression 470 would seem to be:
1) no low octane fuel (aka mogas)
and maybe
2) issues with swinging the prop past compression without damaging kickbacks--
esp with a lightweight starter and/or a lightweight (MT) prop.

If neither of these will be an issue, it seems like a good way to go.