BT hive mind,
My step father has had a '67 172H for about 10 years. He's always asked if I would take it when his flying days are over. Of course I said I would and he said over and over that he wanted it to stay in the family and be available for "the grandkids" if they ever wanted to fly. This was always a "one day" discussion until he died unexpectedly last month. Now I have to get a plan together for what I'm going to do with this airplane that doesn't include selling it.

I'm sure I can do some stuff with it, but to make it a much better option for Idaho, I'd like to upgrade to at least 180hp and it would really benefit from a constant speed prop.

After some research, I've found Penn Yan, AirPlanes and Stoots offering upgrades at various costs, claimed performance thresholds, etc. Does anyone have first-hand knowledge or have gone through this recently?

I know it would be cheaper to sell it and buy a 182 but that's just not in the cards. It has an O-300 now.

Thanks

I have a 172H with the air plains 180hp conversion. It was in it when I bought it so don't know much about it other than what's in the logs.

As far as performance, I love it. It climbs like there is no tomorrow. I don't see much increase in speed, no wind it's 105 or 110kts.

I used to have an older 59 172. It had the O-300 in it. I liked that engine too. Really smooth, really quiet. Nice to fly behind. If you don't need to upgrade, you may not want to.

Feel free to ask any questions you have. I'll answer them if I can.

Thanks for the info Mark. I'm not a small guy and we routinely have DA's over 5k' for takeoff at my field in the summer so this airplane is going to get an upgrade, it's just a matter of which one.

The only thing I don't like about the air plains is the fixed pitch prop, but that may be the direction I go anyway.

Have a fair amount of experience with the Air Planes upgrade with fixed pitch prop. CAP did a lot of these. Like most O-360 installations, it’s pretty bulletproof if not abused.

With the gross weight increase, the full fuel useful load was actually higher in the 172P than in 182R.

Another option for you, AirWorx is now overhauling the O-300, with changes that make it a 170 HP engine.

https://airworxaviation.com

Beware the O-300s are going to the weird area of snakes and conmen like the Franklins did.
Check on that O-300 mod from Airworx. Chris says he has "approval" but really he is overhauling the engine with his mods and then supplying it with a 337 form.

No mention on who approves this 337 but I suspect it is blank of signature from an IA.

They are trying to circumvent the STC process. But your mechanic doing the installation may be on the hook for the Airworx changes.

Chris will send the engine with no paperwork at all other than a log entry that says "Overhauled" and not much else. He says his PMI says he does not need to supply any other info for an overhaul and he keeps all the component tags etc at his repair station to then destroy after 2 years. I had engine overhauled by him two years ago and had to beg to get accessory tags and info for the logs.

There are differences in O-300 cams based on when they were produced. The early cams with pointed lobes will idle at 600 RPM and 10" MAP. Makes torque at lower RPM 2500 or so. Later cams have more overlap and rounded lobes. They will show 16" MAP at 600 RPM idle and make power closer to the 2700 Redline. All of this will change max HP. But usable HP depends on your prop pitch.

Check carb P/N for 10-4895. But I wonder how much power is lost because the O-300 is stuck with the MA3 carb instead of a MA4 carb like the O-320. The later single piece Venturi in both carbs can cause a power loss due to the thicker leg struts. Also the intake turns in the oil sump cannot be real efficient but no mention of porting these only the cylinder heads?

It is also interesting the timing is not restricted by if earlier cylinders like the O-200 and the O-300 has staggered timing instead of both mags the same like the O-200.

If HP is increased by porting and compression how does this all interact?

If your 172 has instrument vacuum Venturis I believe there was an old test at Moffett Field in the wind tunnel where they found a single standard Venturi needed 6.5 hp of engine power to move at 120 mph!

There is a local with ported Superior cylinders from Lycon on his 172. Back to back there is a noticeable difference in performance. I would say 6-7 hp difference you can feel. But not the 5-7 hp per cylinder he said Lyon claimed.

Ben, I think you need to send Charlie a Christmas present after that post.

Wow, thanks Charlie! Tons of info.

I may not be able to bring it out here with the prices I'm getting quoted. Stoots has an amazing upgrade but it's $106k before the install (which is substantial). I'm not willing to put that kind of money into a 172 when it doesn't really fit the bill for me to begin with.

One of my old skydiving buddy's claims to have had a 172 with a CS prop on it at some point but he can't remember the details. I was hoping to find info on it, but no luck so far.

That was probably the old AvCon conversion. The trouble was they did not have a gross weight increase so you lost too much useful load compared to the later Air Plains or Penn Yan conversions. It made a good change for a Cessna 175.

When you find them for sale now the engines are usually timed out with prop ADs to deal with.

Straight tail light stock 2 blade Cessna 182B with a bit larger tires, Large nose fork, a skydive door to make loading and unloading easy and rear jump seats would be my choice for Idaho if sticking to established strips. 180 or 185 is great but they get some wild surface winds when coming home in the afternoons. Nosewheel is nice for being tied out in the wind.

Off airport ops are a totally different set of needs.

Anywhere in the Stanley/ Sawtooth valley in the summer the 172 with O-300 will be not ideal.
Around Meridian it may work fine with the ported cylinders and leave the back seat out for summer.

If I had a choice in the airplane, it wouldn't be this one. I've already got a super cub for Idaho flying and a Murphy Moose project that will be my main ride once it's done. I'm trying hard to find a way to make this inherited airplane an asset out here, it's just difficult with the O-300.

Anything O-300 powered would be a valley airplane for me, I wouldn't take it anywhere in the high country unless I was solo - and then I'd just fly the super cub.

I fly a stock 172H for instruction and I own a share of a 172M with the Penn Yan 180hp conversion. 2 completely different airplanes. 180hp climbs like a rocket. The other day (DA -2000’ish) I got 1700fpm climb and hit pattern altitude before I got to the end of the airport property. Pitch the prop for cruise and you’ll be going….fast enough. Never going to be a speed demon but it’ll scoot as well as any 172 can.

In my experience, the H has just enough to get in the air. It’s a great xc machine because it’s so smooth and you get a lot of time since it’s also slow. I want our flight school to upgrade to something not using the O-300 when it’s time to overhaul.

Therein lies the problem. A change of perspective looks like the only solution to me. It’s a gift and as with many gifts, sometimes we need to grow into them. To be given an airplane is a real treat. Maybe it becomes the Sunday breakfast flight airplane and the only goals are the joy of flight, remembering the person who gave it to you, and working to fulfill his wishes.

Good luck

My vote is yes to the 180hp and no to the constant speed prop. Put on a fixed prop, pitched for the DA you typically takeoff at. The weight savings is better than the (very) slight improvement in cruise speed with a CS.

instead of the weight of the CS prop, do the heavier nosewheel fork

My college flying club converted one of our 3 172N's with the Air Plains conversion back in 1993 and it was a substantial improvement. We debated the available options and Air Plains seemed to make the most sense. Our experienced advisors didn't think the CS prop juice was worth the squeeze on a 172 airframe, and we had a Mooney as well for complex training anyway. 172's should be kept light and simple IMO, and the transformation sure made a great airplane. We got 100 lb GWI if my memory serves, and had to restrict flap deployment to 30° instead of 40°. We did not get bigger fuel tanks, and that might be a consideration if using it for travel. This was before Powerflow exhausts too, and I wonder if adding one of those might wake it up even more.

I recently started seeing Airworx on facebook and their O-300 work looks intriguing. I did not know about the nebulous paperwork and approvals, though, but I would sure do some investigating if wanting to keep your original engine. I do know the latest video I saw with the 170+ hp on the dyno had one Electroair EIS, and I suspect it was using a timing advance...that may be very beneficial at your field elevation.

Just some experience. The guy who owns Stoots was a real jerk over the phone when I called to ask about STCs for my 1961 172C. No idea why but he could not understand why I wanted to buy his STCs. He seemed to think if the airplane needed TW conversion, straight vertical fin and O-360 it was not worth the effort. Seemed odd but ok I won't

That said there are not many options out there reasonably priced. I have heard about a 160hp O-320 installation in place of the O-300 which seems like a good simple swap using factory parts. A light 172I model performs well with the RAM 160hp conversion most elevations and is light/ simple. The H model with the same engine should work well.

The Air Plains O-360 STC has a few oddities. Like the 172N uses a specific black rubber intake hose with heavy wire windings inside to prevent it sucking closed between the Air Filter and airbox.

The Air Plains new Intake box for the O-360 does not line up with the intake opening very well and it calls for a standard SCAT hose which is not for a negative pressure application. This is the problem with STC's going against standard practices but they are "Approved". No way I would make the same change on a regular 172N

I installed a new AirPlains Kit two years ago. They were rewriting the STC but I can look back to my notes and photos for what worked and what didn't. Errors I found.

Penn Yan tried to reuse more parts than Air Plains. So they crammed the larger Sensenich prop into the original spinner for the McCauley. Bending the back plates in the process. Modified baffles etc. Hopefully that has been updated to be better. But it did make a cheaper STC to buy.

Both have options of extending the exhaust risers or buying new exhaust. The only limiter for the flaps is a tab on the flap handle to limit its movement. No changes out in the wing. Funny if the Powerflow makes a HP change like they claim why no flap travel change?

We did have a O-320H 172N here with a H engine and a Powerflow. I hate it and will install a regular exhaust as soon as I can talk the owner into it. It is LOUD. And annoyingly LOUD with a cheap import car muffler sound. How they ever got that STC'd is beyond me. More maintenance to take it apart regularly to lubricate the slip joints per the ICA. I did not see a performance change worth the expense or effort.

For all the O-360 airplanes either STC they seem to need a single pump of the throttle before starting hot. Otherwise they will never start. No idea why.

The earlier airplanes have the restriction to single tank operation at altitude. Later 172s do not. If you remove the headliner you can see they actually welded a tube from the rear fuel tank outlet lines that goes diagonally up to the tank vent crossover above the forward tank outlets. This is unique to the later 172s as far as I know. But genius compared to other airplanes that use Ram air caps and other things as part of a BOTH selection STC. At minimum fuel the air entering the rear lines can cause slugs of fuel to move in the lines with air in between but the vents will allow this air to escape and fuel to gravity feed. Why is there no STC or service kit to install these parts on the earlier 172s??

The other genius thing on a late 172 is the cooling outlet. It is small. Probably 2/3 the inlet size and partially blocked by the nose gear. It also has a tiny lip forward of the opening. Much different than other similar airplanes.

Nobody seems to wonder how this works and they cool so well. It's exactly backwards of how the textbooks say to do it. The only thing I can figure is the later 172 has a vertical baffle from bottom cowl to cylinders instead of a horizontal shelf baffle below the inlets. This causes a sudden slow down of the air as it enters and gives more effective cooling?? This would be the setup to copy if changing from a O-300 to O-360.

Earlier O-320 172s with the same inlets appear to have double the outlet area.

The early 172 fastback has some odd characteristics when flaring at forward CG. I believe they fixed this when they rounded the forward elevator counterbalances and reworked the yokes.

Then later Cessna lost a bit when they rounded the elevator leading edges inboard on the 172P and changed the gear ratio of the ailerons. Less travel but more effort.