Cessna 180 changing -U engine to S,R,K?

I posted this on the skywagon forum too, but as this tends to be an awfully active forum with lots of Skywagon drivers I'd thought I'd ask. I continue my search for a 180 and am keen on using it for float ops and as such have been looking for Auto gas capable planes. Was wondering if there is a problem with swapping out a -U with an earlier, low compression engine or if you could swap for low compression cylinders. Saw a 1977 K model at OSH with an R engine but never found out if it was STC, 337, or simply not a problem because it's all the same TC. I have already searched the archives but all the previous post deal with swapping in the other direction, such as going to PPonk. Speaking of, I know that the PPonk are low compression cylinders but not STC'd for auto gas. Does anyone have any off the record experience with using auto fuel in an O-470-50 or have insight off the record from Steve Knopp on its safety from their testing? Thanks for the replies as this will potentially expand my search criteria.

I own a 1981 180-K, and before I put on the DASH-50 it had a 470U. The 470U was a low compression engine and there were many people who used that as the only criteria for not purchasing a hi compression C-185.
I have never flown mogas in my P-ponk, but with 88gal of fuel, I have never really had to.

BlackFly said:

I own a 1981 180-K, and before I put on the DASH-50 it had a 470U. The 470U was a low compression engine and there were many people who used that as the only criteria for not purchasing a hi compression C-185.
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Not to be a stickler, but that's incorrect. I've owned the O-470 U as well and it is a "high" compression engine. The O-470 A through S on the 180 were all 7:1 compression engines. The "U" is a 8.6:1 compression engine, which was the reason behind the fact that it still produced 230 HP at a reduced 2400 RPM versus 2600 RPM like most other O-470's.

Also, because of this there exists no Auto Gas STC through Petersen or the EAA for the 1977-1981 model 180K.

Back to Matt7GBC's question...I don't know of any STC to remove the U and replace it with a J,K,L,R, or S model. A creative field aproval may yield the best results. Also, I would call texas skyways about the low compression work they've done. They've done quite a bit of piston swap STC's in the past and they may have a direction to point you in.

Good Luck,
Bill

Matt,

The only 180s that came with the 0-470U motor were the K models. Your desire to use mogas would be easier if you just scratched the K model off your list. The TCDS specifically links motor model to airframe model. Variation would require approval.
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/417858c7f90969f7862572430064d352/$FILE/5A6.pdf

My Pponk STC states "100LL only". My engine has run a time or two on car gas out of necessity. I won't use car gas as a regular diet in any airplane but if that's all there is to get home with? It seems to work.

Stewart

Thanks for the feedback, sort of what I had expected. I had been looking at the F - J models, but keep seeing K models that are more of what I am looking for, except the -U engine with high compression cylinders. When I had the citabria on floats, I could not have done many flights (without becoming stranded) if I had not been able to burn auto fuel. I am not concerned in the short term as I would initially keep it on wheels, but would like to have options come overhaul time. Perhaps the Pponk's capability for low octane in a pinch is what I should keep in mind.
Thanks again!

Matt,

A friend of mine runs his late model 185 on floats and has the same issue with fuel availability. Most of these late model planes have 84 plus gallon capacity. What many do, I'm told, is leave enough avgas in one tank for takoff and once up at cruise and much lower power settings...switch tanks to your "emergency Auto Gas" tank.

Please take that at face value, and not a recommendation of what you should do or what is legal. I just know that many people have run car gas in that fashion to get them out of a bind in the middle of nowhere.

Properly applied it won't hurt your engine. Think of all the 185's and 206's in Alaska and Canada. If anyone thinks that they are being run on avgas 100% of the time...I've beach front property to sell in Lubbock.

I second what N4653B just said. I have been with a friend in Louisiana flying a 185 on floats and jockeyed the plane around to get close enough to the unleaded hose at an oil rig in a pinch.
Marty

According to an old Petersen Aviation pamphlet, the O-470-A, -E, -J, -K, -L, -R, & -S are all aproved for 87 octane cargas. Also the IO-470-J & -K.

Rooster

Talked to Steve Knop for almost an hour today. The reason the P-Ponk isn't approved with Mogas even though it is a low compression engine is because the Feds drug out the certification for so long and then told him they could go ahead and approve it if it weren't for the mogas issue. He said to heck with mogas and got his STC. The thing will run on 80 octane at 7.5 to 1. I was very impressed with his knowledge and his willingness to share it. I am much better informed because of his generosity. Hope to put a P-Ponk O-470-50 on a Cessna 180 real soon and maybe on a C182.