What's the biggest 180 motor that can run on mogas?

I met a pilot up in Colorado last winter who has a Pponk Powered 180, 260-270 hp IIRC, and he told me that you can run Mogas through it. I've looked for the info and can't find it anywhere. It would be nice to have a souped up 180 with mogas capability.

So what is done to get this extra horsepower? Do they stroke them? Likely not anything that would increase compression ratio, else you lose your mogas flexibility. Can't run higher RPM, or props lose efficiency. Only way is to increase displacement, right? That means stroking or overboring, but then it's not a 180 anymore... just an O-360 case and cylinders.

What's the biggest engine available by STC for a Cessna 180 Skywagon that you can run mogas through? Hope that makes more sense. Just changed the title also.

As you know, it is all about compression ratio. I run a low compression (7.5:1 ratio if I remember correctly) O-540 in an experimental Bearhawk. With some minor tuning mods, it is putting out ~250hp and uses mogas just fine. The 260 hp models require 100LL due to a higher compression ratio, so that seems to be the break-over limit for Lycomings, anyway. I think it is similar for Continentals when stepping up from say an O-470R (230hp) to 520's and larger. Is there an O-720 conversion for a 180 out there? That could certainly do it albeit with a significant weight penalty. There may be some experimental variants that can push the hp a little higher on mogas, but I can't recall any off hand; they couldn't be used in a 180 anyway. A good electronic ignition system would help push the detonation limits; the guys I know who do that don't really know where the timing limit is until it's too late. That gets expensive in a hurry! They rebuild, back off the timing a little and hope for the best with the new rebuild. I'm sure there has to be a better way, but they haven't found it. That is with an LS1 engine and they are notorious for detonating, anyway.

4Whitey wrote:What's the biggest engine available by STC for a Cessna 180 Skywagon that you can run mogas through? Hope that makes more sense. Just changed the title also.

I misunderstood... Thought you were taking about 180hp motors for some reason. Disregard the O-360 bit.

The Pponk is low compression and will burn mogas just fine however there is no mogas stc for this engine. I don't know of any upgrades for the 180 which would allow legal use of mogas.

Could a non-experimental Pponk O-470-50 or a low compression O-550 do so without hurting the engine/fuel system?

66skylane wrote:The Pponk is low compression and will burn mogas just fine however there is no mogas stc for this engine. I don't know of any upgrades for the 180 which would allow legal use of mogas.

I posted before I saw your reply, thanks.

So if the Pponk can run mogas OK, what would be done to it to get it certified? Different seals, float, fuel lines?

Whee:

P-Ponk conversion engine (designated as 0470-50) is a 470 case with 520 cylinders bolted on it. The engine is certified with 7.5 to 1 pistons, but you can get a field approval for 8.5 to 1 (in mine). There are also STCs for conversion to straight 520 and 550 engines too.

Whitey:

Previous posts are correct, there no STCs for car gas with the PPonk 0470-50 or the O520 and O550.

If you search the 180 site, I think you will find some threads of folks who are mixing and claim that it is working well, but I have never tried it and can't give you any personal experience. I have done this search too since those 550s are pretty thirsty (I can dial mine back to about 11.5 gl / hr and still get 135kts) and it would sure be nice to be able to use cheaper gas, but I don't believe there is any way to do it legally. I can tell you that a number of years back, i had an engine out and although I landed without incident, i received a visit from the local FAA. The first thing they did was test the gas. I remember thinking at the time that I would have probably regretted mixing gas had I been doing so. Food for thought....

Good luck with your search. Looks like you are a family guy and I can tell you that the 180 is a pretty good family ship. I have 4 kids and have had some really good times with them and the wagon. Good luck with your decision.

Regards, Larry

I ran mine for 750hrs. mostly on auto gas. Figures it saved me roughly $20/hr. No issues. I'm more concerned with snow thn autogas,
Gary

Steve Knopp tried for several years to get mogas certified in his engines but finally told the feds to piss off so a low compression 470 is it

I think Steve Knopp tried to get mogas approved for his P.Ponk 470-50 engines but it was not done to the level of additional paperwork .I know of lots of P.Ponk 180 Cessna's out there flying . Compression of 7 to 1 is OK for mogas or it's replacement.There is a service letter or bulletin against using higher compression pistons in the P.Ponk motor. 100 LL is roughly 2 bucks a gallon more than mogas. Non ethonalole fuel is available here for $4.30 a gallon , I have about 250 gallon tank with pump on trailer.

Don't forget, octane requirement decreases w/ altitude, so if one always flys high, perhaps one could take off and climb on 100LL, then switch to Mo gas for cruise, don't know exact numbers for octane requirements vs. altitude, though. I don't know if the TCP research guys would know, if they are still around.

I am wishing that if Swift Fuel becomes approved, perhaps all the alcohol producers could be switched to Swift Fuel, thus no more alcohol problems?

Isn't fuel injection a factor too? I didn't think there were any injected motors that can run MoGas?

blackrock wrote:A good electronic ignition system would help push the detonation limits; the guys I know who do that don't really know where the timing limit is until it's too late. That gets expensive in a hurry! They rebuild, back off the timing a little and hope for the best with the new rebuild. I'm sure there has to be a better way, but they haven't found it. That is with an LS1 engine and they are notorious for detonating, anyway.

I'm curious what setup your buddies are running...

I built an LS1 with 11.2:1 SCR and ran ~25° timing at WOT. I used the stock engine management, just reworked the maps to fit the engine alterations. Still runs great, 5 years later on 93 octane. Thanks to a great combustion chamber design, LS1's are pretty resistant to detonation.

The LS1 has a good knock sensors in the valley, I'm not sure why someone wouldn't use them.

macktruckfarm wrote:Don't forget, octane requirement decreases w/ altitude, so if one always flys high, perhaps one could take off and climb on 100LL, then switch to Mo gas for cruise, don't know exact numbers for octane requirements vs. altitude, though. I don't know if the TCP research guys would know, if they are still around.

I am wishing that if Swift Fuel becomes approved, perhaps all the alcohol producers could be switched to Swift Fuel, thus no more alcohol problems?

I had this discussion about altitude and auto fuel with Ly-Con Visalia when reworking my 180 (HP) to 10:1 pistons. I got the go ahead with the following advice. The manifold pressure is the gauge to watch and is the early warning system on detonation, which is what we are trying to avoid. Low density altitude ops, cold temps and WOT with low octane would give the worst combination. They suggested limiting 26 or below manifold pressure to provide the saftey net.

Concerning Swift fuel, franchise costs for duplicating their formula and the comparative profit levels to ethanol and the RFS rules will determine how much we see.

flyingzebra wrote:Isn't fuel injection a factor too? I didn't think there were any injected motors that can run MoGas?

Zebra, is that something you heard in regard to how well injection works with the fuel? Or simply in regard to applicability of the STC for mogas for the various engine models?

66skylane wrote:The Pponk is low compression and will burn mogas just fine however there is no mogas stc for this engine. I don't know of any upgrades for the 180 which would allow legal use of mogas.

I heard they tried for an approval but the FAA wanted them to test the fuel from all fifty states.

flyingzebra wrote:Isn't fuel injection a factor too? I didn't think there were any injected motors that can run MoGas?

The Debonair with a IO470 is approved for auto gas, which makes it a very tempting aircraft.

Obviously it's more about the approval process rather than what works.

A buddy flys in Indonesia, and they would love to have an auto gas 180 with more power than the 0470. No solution as far as they have found.

I've searched a couple of times for STC's for MoGas for a few different injected motors I've had and haven't found any. When I asked around I've been told that, because of a higher vapor pressure and lower flash point, MoGas has some real risk of causing an injection system to not function properly at altitude. Nothing I've ever really substantiated or dug too deeply into. Always just looked enough to not find the STC's I was looking for and went away pouting.