The 150hp has the advantage of being able to use auto fuel. I had an L model, same engine. With just two pilots no bags, local flights, not much advantage to 180hp, but if you're traveling some distances, the 150hp peters out around 9000' in Texas heat. I had mine to 11,500' a couple times, but took time to get there.

There is a Peterson auto fuel stc for many 160 hp o-320 installations. The only catch is 91 octane is required rather than 87(which is a lot cheaper).

and, some of those STC's require a fuel pump and/or fuel lines change. I don't know if that is the case here but check, don't assume it is just a sticker

I got a 160 hp 172 to 15,000 once in Mexico to get over weather when I was not sure of how to pick up an enroute IFR clearance.

Own a 180hp/csp 172 Avcon conversion which I’ve had for 20 yrs. At age 78, flying 1500 mile xcountry out west between texas and west Washington, the horsepower/CSP/powerflow exhaust comes in handy, especially with long range tanks. Would I spend the money to upgrade, no.

I've flown several 172s with the Air Plains 180hp mod and really like them. With Air Planes you get a small useful load increase, and with the small tanks you can take full fuel and four friendly people. The performance increase is noticeable, and they feel kind of spritely.

75% power is right about 10.5 gph, giving you 3 hours plus some reserve. Do you really need more in that plane?

Slightly different boat for me, but my recently inherited 172 is a 145hp model (O-300 engine). I've been pricing out 180hp conversions and they are all $80k+ (mostly way ++). I have been unable to find a paper-only STC available that I could find my own O/IO-360 and put on the plane. I just don't see dropping $85-100k on an $80k airplane... so frustrating that there aren't other reasonable options for (arguably) the most popular trainer in history.

I did my PPL with a flight school that had two 172's - one with 160 HP (I think? Could have been 150) and one with 180 HP. Due to maintenance issues, I probably split my time about equally between them.

Both were great planes. The 180 had a lot more takeoff power, especially on hot days. My instructor was a large guy and it felt much safer on take off when carrying a lot of gas.

The 160 flew better and both my instructor and I thought it felt more "balanced." It had 40 degrees of flaps, where the 180 did not. I generally preferred the 160 and ended up choosing it to take the check ride even though both planes were available. It was easier to do short field landings and stalls with the extra flaps.

Probably can't go wrong either way, but I would not have said the 180 HP plane was "better" all the way around for basic flight training stuff. I did not ever use either one as a traveler or family hauler or in the mountains. I expect for those missions you'd want the 180 HP.

The airplane is probably worth more than you think. We just overhauled the O-320 on our 172P and hung a new prop and it appraised at $140k for insurance. It's in average condition with newer paint.

If you’re gonna be a bear, be a Grizzly!

Call Stoots and get the IO-370C1F (190hp) STC.

What’s the reason not to do it?

20-30hp sounds like a big improvement.

Is density altitude in the summer a concern? Seems like the extra power would absolve that.

Great comments! My 150HP has the autogas STC currently but it’s not readily available. I’ve never used it. I’m wondering if my prop will be repaired ($1800) or will require new ($10,000). The conversions get a new prop so if insurance covers a new prop…that makes the conversion that much more interesting. I paid $86k for it in feb 2020 (yeah, that feb 2020) with mid time engine. I put 60k in the panel to teach. I’ve generated $46k in my reserve account over 1000hrs. If insurance pays $20k…I’ve got $66k to spend. Will take $80k for conversion…for an extra $14k, I have a 3500 TT 172M with full Garmin and new FWF180HP conversion. Kinda now or never decision.
The 150HP has been perfect for my use for 5 years…I may stop teaching for a couple of years… I bet I go back to it if I stop…I enjoy it. Probably won’t sell it for a long time.
It’s hard for me to pass up owning such a capable 172 for an extra 14K…but don’t ‘need’ the upgrade.

Waiting on insurance to answer my questions so that may tip one way or other. It’s never been a flight school plane (except for me…but it’s flown and treated like a personal airplanes low number of flyers). Previous owner had it 30 year, hangar kept.

These planes just aren’t easy to find, and it’s not getting better so inclined to make it even better. Well see…

Chad, we had a prop strike on our 172P. Avemco paid for the the new prop and labor, and they paid the cost of the prop strike teardown. We applied that cost to a full overhaul since we were close to TBO anyway.

I'd bet the same applies to your insurance and you'd pay the difference for the upgrade, and I don't think the cost difference in the props is that much different.

If you need more help jumping off the cliff... even if you only instruct for a couple of years and then sell the plane, an upgraded 172 will sell faster and for more money than a stock one.

A few thoughts like about the Air Plains. ( I have owned one in flight school and maintained 5 more). 172N and P

1. They remove the black intake duct between the air filter and the carb airbox. This duct is reinforced with an external heavy wire. The STC replaced it with standard SCAT hose which is clearly stated as NOT for a negative pressure application.

2. The Current Air Plains kit as of 2 years ago came with a new UMA airspeed indicator. It works like crap. Sticky and slow to register on takeoff. All of the numbers are evenly spaced on the dial which older airspeeds never did based on the spring windup in the instrument.

3. The firewall mounted battery box with the 24V airplanes is very close to the rear of the left magneto. It needs a big notch taken out to clear. The best way to fix is change it all around to a battery tray and manifold battery with bolt hold downs. But the change is a bit vague as to what is allowed and how to install.

4. When starting hot. Every gravity feed O-360 172 needs one single pump of the throttle to start. Otherwise you're sitting there cranking and cranking. But one pump and then it fires off. No more no less than one. No idea why.

5. The 160 hp O-320 performs almost as well at low altitudes average temps and does fly/ handle a bit better. 40 deg flaps are nice. Even the H engine works fine.
The 180 will cruise at a lower RPM for the same speed and so is quieter but not always as smooth. The 2550 Gross with the 180 is a must for scenic rides and really makes a difference staying legal.

6. There is no comparison to the 180 O-360 and the Power Flow Exhaust. I have flown examples of both and before / after conversion. No substitute for cubic inches.

7. Air Plains baffles use a lot of tinnerman nuts with pointed type A screws. No No. With Tinnermans type B thread is required. Still looks like a self tapping screw but with both together you can see that the Type B is finer thread pitch. Though still coarser than a machine screw.

8. There are shock mount spacer washers reused from the original mount. Don't forget those or the mounts almost touch the engine case but there is a gap when torqued.

9. Hot and over trees loaded I want the 180 for sure. But Air Plains seems more focused on advertised cruise speed instead of a climb prop setup.

10. Air Plains was rewriting the STC manuals and trying to get the paperwork better. It's one of the few engine upgrade STCs with actual performance charts. Not just "Performance is same or better than original" legacy STCs.

11. The Air Plains is a nicer conversion with a new engine not a converted one to make an O-360 like some of the Penn Yan conversions.
Penn Yan modifies some original baffles, Airbox and the spinner to fit.

12. Air Plains has new baffles. Get the new muffler and exhaust option if you can instead of welding on the extensions to the exhaust pipes to fit the wider cylinder port spacing. But like anything the Air Plains is more expensive.

13. I found Air Plains had ordered my engine with a Sure-fly Electronic mag. I got that canceled for dual magnetos instead. I don't want an electronic ignition with 24V after field reports of failures.

14. I prefer the Piper swivel for wire mixture and carb heat controls over the drilled bolt Cessna and Air Plains use. Yes I know not to the STC but I believe it is a superior attachment method.

15. Challenger Air Filters I throw away. No gasket retaining lip to prevent gaskets from being ingested. Before the Challenger STC was issued Brackett had an AD for gasket ingestion and accidents. So they redesigned with a filter housing having a lip to retain the gasket. Challenger was STC'd after this AD was issued and have had accidents due to the gasket being ingested.

16. Go to the Dynamic Propeller website and see what airbox reinforcements and cable guides they have. Good products that seem to help. http://www.dynamicpropeller.com/

17. Air Plains with lightweight starter. The starter does not really fit the nice powder coated baffles. other cylinder baffle parts needed trimming but now your modifying finished powder coated parts. The engines are all the same so they need to fix the tooling so they fit correctly.

18. The 3 Cylinder primer kit adds cost but is worth it. Also add a manifold pressure gauge. It's a much nicer way to set power or have a percent HP indication on engine monitor.

I tried to price out a Stoots conversion for my O-300 172C a few years ago. I was trying to get pricing for TW conversion, 370 and square fin/ rudder STC because I had a buyer for the airplane who wanted to have the conversions done and then take it to Alaska. I had a square fin and rudder plus gear legs, tailwheel and parts. He was direct about why would you even want to spend the money to do that. Hello aren't you the guy selling the STCs.