generally speaking, more octane is better than less octane. car gas doesn't really provide anything good and brings along the undesirable ethanol unless you can find gas that doesn't have it in it. so, aside from being cheaper, i don't see what auto gas would do for you. If you don't mind the cost, keep using 100LL and you'll be ok.
you probably know this but here it is for someone that might not, octane isn't necessarily about power, it's about how smoothly the fuel burns in the cylinder. higher compression engines need higher octane fuel, lower compression engines don't. high compression engines will knock/detonate with lower octane gas where low compression engines will not run any better or worse, generally speaking, with higher octane fuels. besides, the lead in the 100LL is good for your engine, as far as I know, autogas doesn't have lead anymore.
Bob , are you saying you use 75% regular auto gas ( Not the high octane , ethanol free .) to 25% 100LL mixture in your small Continental ? I have a 90HP in my Champ and am wanting to learn what works best ! Thanks ,Randy.
Yes. I do not measure it exactly. My motivation is to keep the lead fouling to a minimum, and it works. I almost never have spark plug problems.
The $ savings is minimal - regular car gas is $3.80 or so, and we have a self serve Avgas facility at KSEE that charges $4.25 for 100L.
The alcohol is an issue, legally, since the STC prohibits it. It does not seem to hurt auto engines and carbs from the 1960s, and back then, the major difference between auto and aircraft engines was the water jacket. I have the feeling that a nasty insurance company would disown you if they found alcohol in your fuel blend. Here in California, I believe the insurer would have to prove the alcohol caused the incident before they could cut you off.
Regular car gas is around 89 octane - well above what the small Continental requires. Old avgas was 80-87, two points less than auto.
Bob , thanks for the info. Sorry for my late ( thank you ) reply but my I Pad has been down . I appreciate your on-line knowledge , now if I could get you to move closer to Missouri so I could use you as an instructor !
It was 68 degrees and cloudy here today. It is usually 73 and sunny. It is rarely anything but gorgeous. The only thing marring the paradise of SoCal is - there are way too many people here for existing housing, water supplies, and freeways.
Missouri is beautiful too, but I am really, really spoiled. I haven't seen a mosquito or a gnat in literally years.