Frank,
In 29 years in aviation, I've heard the "old Wives tale" that mogas will cause vapor lock. At altitude. 14.800 feet is considered by many as vapor lock territory, yet there have been autos atop of Pikes Peak for decades.
Vapor lock happens when fuel boils as a result of lack of pressure. A weak pump in a hot area is indeed ripe for VL, but altitude did not a cause it, lack of pressure did. And most certainly, the archaic Lycoming would not.
One of EAA's test beds included their test 150 with a "special brew" that would have boiled on the ground in mere sunlight. The 150 struggled all the way up to as I recall to nearly 20K. No VL occured.
Some old manuals such as Piper Cubs, recommend using gasoline available at the gas pump, including illustrations of such. AV gas was an option. Mogas during the heyday of the Cub was nothing like it is today, in octane numbers unleaded included.
Bottom line, we can trash this topic to death, but aviation has to get it's own head straight. There is nothing wrong with mogas, and it's about time aviation begind enbracing electronics, which now have beeb around longer than Lycoming has attempteds to figure out how to prevent crank failure.
Maybe when lead will cease to exist, and no lead is present to contiminate oil, who knows?
My comments on the useage of mogas and it's benifits, includes Lycoming, Continentals, and Rotax over a period of 21 years.
The Conti I mentioned has been using 87 since the STC became available. It has most definetely improved it's reliability. A few years back, when the "dreaded" MTBE was in use, and some claimed that it will spoil if let standing, and ruin all sorts of components, said C182 accumulated a whole 4 hrs, and during it's first time out. That gasoline had nearly 12 month to sour.
I signed off the annual, and the owner was concerned (and a firm believer in mogas), it fired up on the 4 th spin of the prop, and exibited no ill effects whatsoever. This was some 12 years ago.
The fact that Lycoming is coming around to mogas is a step in the right direction. Now if we can only add electronics.
TT
RV10/Mogas