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I use 87 Octane gas in my 55 Pat which has 1956 heads so it is supposed to be 9.5:1 CR. I've never had a ping or a hiccup. It has stock cam and stock timing. Go figure.

Of course, I'm at 2,700 ft altitude, so the dynamic compression is certainly less than it would be at sea level. According to a chart I found on the web, 2,700 ft altitude would be 13.3PSI rather than 14.7 at sea level or about 10% less dynamic compression.

Craig

G'day all, I have around 40 vehicles on the road and i find that for vehicles that i don't use very often, i add a few litres of Avgas, which has a shelf life of 10 years, compared to todays possum piss which is good for maybe 6 months. I agree with V8 about the premium grades being more stable, although we have found that they run slightly hotter in the old pre 40's motorbikes.
Use the best gas that you can get...nowadays, you never know how much recycled crap is in the bowser. in Australia, we get thinners, recycled E85, reclaimed Diesel and surplus ethanol fuels into our 91 "regular"....coz...they don't have to declare it until it gets to 10%. I have had some real headchecks lately as the fuel just smelled like crap as I was putting it in the tank.

Best Regards, Peter Toet