I would just self insure and get a MU2 or Citation. From what I have read on the internet they are cheaper to run than a Skylane.

Chris, not exactly what you asked...but would it be reasonable to buy a 182 that used lower octane fuel...in case 100LL, or expensive 100 octane, became expensive?


(I've had that thought, before)

Oddly enough, that may be somewhat true.

The certification standards for engines changed at some point from typical max power to minimum max power. This meant an engine certified some time ago as 230 HP might now only be certified to 220 HP to be sure it made at least this power under the worst case conditions.

So depending on the date of certification, a newer engine with the same nameplate HP might be more power than an older one.

I don't recall the details of this change, but I recall reading about it in a magazine.

Mike C.

The -U Continental and 540 Lycomings are basically high compression 260 hp engines that are derated to 230 hp by limiting rpm. This is one of the reasons they provide better cruise and altitude numbers than the previous low compression models. Same idea with the 172 Hawk XP, 210 hp engine turned down to 195 by limiting rpm.

Turn the rpm back up and instant hp boost!

Jeff

Fuel injection:

When upgrading to the IO520-F in my '75 182, I chose to have it carbureted instead of injected for a few reasons.

It would have been about another $12K to run the return plumbing back to the tanks and modify the firewall for the FI header tank, wire and install an electric boost pump. The 520 with a carb is a drop in replacement for the 470, with a little trimming of the inner cylinder baffles for the slightly larger cylinders.

Then If I'm stranded with a dead battery, there would be no hand propping for a start. The carburetor is so reliable, no issues since installation more than ten years ago. No clogged injectors or trying to tune the injectors. A downside is you have to be alert to carburetor ice with the carburetor, and I wouldn't be without the Carburetor Air Temperature Gauge.

Although one might think that carb ice is more a concern with low power approaches than climb or cruise, the opposite is true. Watching carb air temp gauge, it goes way up out of the icing range when the throttle is brought back for approach, but I've had ice on full throttle climbs; more venturi cooling effect creating ice. I don't normally use carb heat on approach but monitor the carb air temp.

IO550 C182’s are sooo last year. You need a Wipare Boss!

viewtopic.php?f=49&t=116388

Frankly; I like the reminder about the Mogas STC for the C182 … seems that some of the (low compression) P-Ponk installs are also using Mogas inspite of the STC limitations.

Yeah, I'll take a Whipair Boss Doug, just send me a blank check to buy one.

Re Mogas, another reason I bought the Texas Skyways IO520-FTS is they hold the STC to install 7.0:1 pistons to replace the 8.5:1 to allow the engine to run on Mogas. I'm not sure what the horse power loss would be, but still more horse power than a 470; I think it would be 265 like the 7.0 Pponks. Some of the take off horse power loss could be recovered by turning up the governor to the 2850 max RPM the IO 520 was certified for from the STC'd 2700.

Of course the "mogas" I would run would be the 92 octane Pure Gas sold near me by the 55 gallon drum for $5.50 a gallon. No ethanol, no lead, but I really don't want to go thru that trouble and expense and will just keep paying the high 100LL prices, throttled back.

I didn't know that. I have a Texas Skyways engine in my 182. I'll keep that in mind.

Aubrey: With imitation being the sincerest form of flattery, I am getting inspiration from your panel: I am doing my 180 as the "last one", and have questions.
PM sent to avoid thread drift.
Note: Steve Knopp was doing fish spotting when he developed the O-470-50 "PPonk" engine. Because of his need for long flights over water, he purposefully used low compression cylinders for Mogas use. Now it makes even more sense, with fuel prices as they are.

I didn't know that. I have a Texas Skyways engine in my 182. I'll keep that in mind.

I was intrigued by this question, so I did a little "research" (meaning I searched the web for info that sounded right, so all of this could be wrong).

Turns out there are websites that can "compute" the power change for a compression ratio change for folks modifying their cars. Ironically, they are trying to increase CR usually, and they end up buying 100LL from airports to power them in some cases.

So if we assume that same formula applies, here is an example calculator:

http://www.wallaceracing.com/hp-cr-chg.php

The IO-520-F out of the box is 8.5 to 1, makes 285 HP, 2700 RPM continuous, 300 HP, 2850 RPM takeoff 5 minutes.

Putting in 7.0 pistons and assuming the above formula is correct, then we get 274 HP, 2700 RPM, or 288 HP, 2850 RPM, a 4 percent loss.

This is a lot less loss than I would have intuitively expected from an 18% compression ratio change, so much so that I am suspicious this formula might be wrong. But if it isn't, that seems like a tolerable power loss to get off 100LL. Basically, put in a bigger displacement engine with more HP, and then derate it with lower CR pistons, but you still end up with more power than the original setup so the plane will not be under powered.

It feels like 7.0 is more reduction than would be necessary if you had "premium" unleaded fuel, like UL94 or maybe premium mogas. Maybe 7.5 would be enough? That would take testing to be sure.


That works, but it is a 5 minute limitation and the prop will be somewhat less efficient, so you don't get as much benefit as the numbers imply. It will also be noisier.

The lower compression ratio has one other effect, it lowers engine efficiency. You will burn more fuel for the same power. Based on what I can find online, that seems to be about a 5% hit for a change from 8.5 to 7.0. The plane will use about 5% more fuel to fly the same speed. That means reduced max range and/or increased fuel weight. You are also buying 5% more fuel, so the unleaded fuel has to be at least 5% cheaper to have parity, which seems likely versus the unleaded 100 octane contenders.

Mike C.

I was intrigued by this question, so I did a little "research" (meaning I searched the web for info that sounded right, so all of this could be wrong).

Turns out there are websites that can "compute" the power change for a compression ratio change for folks modifying their cars. Ironically, they are trying to increase CR usually, and they end up buying 100LL from airports to power them in some cases.

So if we assume that same formula applies, here is an example calculator:

http://www.wallaceracing.com/hp-cr-chg.php

The IO-520-F out of the box is 8.5 to 1, makes 285 HP, 2700 RPM continuous, 300 HP, 2850 RPM takeoff 5 minutes.

Putting in 7.0 pistons and assuming the above formula is correct, then we get 274 HP, 2700 RPM, or 288 HP, 2850 RPM, a 4 percent loss.

This is a lot less loss than I would have intuitively expected from an 18% compression ratio change, so much so that I am suspicious this formula might be wrong. But if it isn't, that seems like a tolerable power loss to get off 100LL. Basically, put in a bigger displacement engine with more HP, and then derate it with lower CR pistons, but you still end up with more power than the original setup so the plane will not be under powered.

It feels like 7.0 is more reduction than would be necessary if you had "premium" unleaded fuel, like UL94 or maybe premium mogas. Maybe 7.5 would be enough? That would take testing to be sure.


That works, but it is a 5 minute limitation and the prop will be somewhat less efficient, so you don't get as much benefit as the numbers imply. It will also be noisier.

The lower compression ratio has one other effect, it lowers engine efficiency. You will burn more fuel for the same power. Based on what I can find online, that seems to be about a 5% hit for a change from 8.5 to 7.0. The plane will use about 5% more fuel to fly the same speed. That means reduced max range and/or increased fuel weight. You are also buying 5% more fuel, so the unleaded fuel has to be at least 5% cheaper to have parity, which seems likely versus the unleaded 100 octane contenders.

Mike C.

This is really great information for a “worst case” scenario, where 100 octane fuel becomes unavailable or unreasonably priced, or one entity has a monopoly on it.

I’m pleasantly surprised that such things already exist.

I had the Baron “President” that spun the props at 2850 RPM. It sounded just fine inside the cockpit

I has the Baron “President” that spun the props at 2850 RPM. It sounded just fine inside the cockpit