I have the Petersen STC for my Cherokee 140. Same O-320-E2A engine. It runs perfectly fine on mogas, though I usually burn premium unleaded or a mixture of 100LL and mogas. Watch out for mogas with ethanol in it, it's almost everywhere across the USA anymore. Fortunately I can still get alchohol-free mogas here. I use the simple water bottle test to detect alchohol in the mogas.
Auto fuel will keep your plugs cleaner and your oil will not turn as black between changes either. There are a bunch of folks with opinions on it all on both sides. All I can say is that I had a Warrior 151 and flew it 750 trouble-free hours in 2 years on mostly auto fuel. I ran the 87 octane, as the 150 HP engines are 7:1 compression and need premium about as much as your lawn mower does! Your engine was certified for 80/87 octane. I do not see where there is any benefit to running a mix of 100LL. All that does is add lead and octane to the mix and your plane needs neither. Stay away from ethanol... and do not let your plane sit longer than 3 months with auto fuel. Auto fuel does not have the shelf life like 100LL. The only real reason 100LL has it is because they only make it a few times a year because of the hassle of getting the refinery cleaned out of the leaded fuel so they can make more unleaded. As a result, they put stabilizer in it so it lasts longer without varnish. This is not a problem so long as you fly the plane regularly.
My 74 Warrior has had mogas for the last 15 years. I'm lucky to have a nearby airport with mogas on the field (no ethenol). I only run the blue stuff when I'm on a trip. I fly regularly and have never had a problem with it.
Check with Peterson. I have an Arrow and there is no STC for an Arrow, yet the engine has one when used in other planes. Admittedly I have burned a boatload of 93 octane unleaded in it and it runs fine, compressions all in the high 70s, plugs and oil stay clean... and the wings have not fallen off. If your engine was originally certified for 80/87 than regular will be fine, if it has higher compression and called for 91/96 or 100/130 or 100LL than it will need premium so that you do not have detonation (pinging) which is very bad for the engine. It certainly is not approved.
Hey guys, a word of caution. The new Federal Energy Plan requires the refining industry in the US to use 9 billion gallons of ethanol this year. This requires that almost every gallon of gasoline sold this year will contain ethanol. For example of the four petroleum terminals available to central Wisconsin three have already announced that they will no longer carry conventional gasoline and the fourth has not announced their intentions yet.
Some suppliers do not label the ethanol as they are supposed to. Know who you are buying motor gas for aviation use from.
Gary
