I would not "overestimate" the effect of the lower air density at higher altitudes here in CO, that lower density's effect on gas engines and detonation is offset by our super low humidity and high summer air temps. I had chronic pinging issues in my old 360 until it finally busted a ring land and cracked a cylinder; it was a 1975 360 LA block bored .060" over with KB flat-tops at zero deck, stock crank and rods, stock Magnum heads and rockers, Lunati Voodoo 256/262 adv. duration hydraulic FT cam (too small), Air-Gap intake, shorty headers... It measured out to 10.42:1 SCR and I had cranking compression only around 160 psi but on hot summer days even with fresh premium 91 in the tank and total mechanical advance of 32* it would ping like a mf'er if I opened up the secondaries in 2nd or 3rd gear (904 trans with 2.94 rear gears). This was when I lived in Denver, then the first year or 2 I lived in Fort Collins so the elevation was usually 5000-6000'.
