Has anyone found a less expensive STC for mogas on a 0320 E3D 160 conversion? EAA doesn't have one for this engine with the 160 hp and Petersen wants $2475.00 for the STC with a dual fuel pump deal and some new fuel plumbing. I really don't understand what difference it makes if my pistons are flat on top or pointed.....but it seems to cause a 2475 dollar issue....Has anyone found another STC from somewhere else that might cover this engine?? thanks John

The responses here are the same that I found when researching. It makes me think I'm better off not to get the 10 hp increase. I'm lucky enough to be able to buy mogas at a nearby airport, and with the prices I'm seeing for the blue stuff, I think I'll stick with 150 hp.

MoGas vapour lock on a Cherokee with 160hp or 180 hp under the cowl on a hot summer day in the hotter southern and southwestern US climates is very real due to the extra heat outputs of these engines. I've experienced vapour lock, on the ground thank goodness, in a 150hp Cherokee 140 with autogas one hot summer day. In the fall/winter/spring seasons when the ambient OAT never rises above about 70F at the hottest part of the day, autofuel runs wonderfully well in these planes, keeps the sparkplugs very clean when you're running the richest mixtures, but as soon as it warms up enough that you need to lean the mixture a lot on the ground, and lean for takeoff due to high density altitudes in warmer temperatures, you really want to stick with avgas.

I had a Warrior with the STC and flew it 700 hours in 2 years using mogas almost all the time. You could not find it sometimes while traveling. My plug and oil always stayed clean, and the compressions were always high 70s. I am a firm believer in unleaded for keeping things clean. The nonsense about the valves and all that is nonsense. All these engines have hardened seats installed, so valve and seat wear is a bogus old wives tale. I have an Arrow with an IO360CIC. It has fuel injection and is 8.7:1 compression. There is no STC for it to use mogas, however, Petersen suggested it is only because they need 2000 hours of testing to get it approved and the expense is not worth the return on Arrows, because it is not as common and they do not think they would sell enough STCs to warrant the cost of obtaining one. The engine, due to the compression, needs 91 octane. Like Gary G., I've done it. It is certainly not approved, but I have burned enough of it from sea level to 12,000... and I live in Florida and it is hot here... to tell you it runs fine. 200 hours and the plugs look like new still. Oil comes out clean at 50 hours. Engine runs great and compressions are all over 77. Never had any vapor lock problems with it. I did, once, on a take-off roll with the Warrior have a vapor lock kind of stumble just after full power in the heat of the summer and after a hot restart. After that I included a full power static check in my run ups... but never had it again. There is no alcohol in the fuel in my area. I would caution anyone from using fuel with any alcohol. It will harm pumps and things... and is much more likely to give vapor lock.

I have see the topic of mogas conversions come up several times. At what point does this become financially reasonable to do? Figure the coversion cost, increasing cost of all blends of fuel, availability and operating drawbacks. I know of a guy that does this but sometimes I think it is because he has more time to mess with it and he is always doing something different.

I am not trying to knock the practice. But just couroius.

That gives me a better perspective. Thanks.

One other thing to think about is that mogas is almost unavailable in most of the US in 2008. Check if you can even buy the stuff before you put money and effort into the STC. Check AOPA they had some blurb on the changes in mogas of late.