gearheadE30
I'm Awesome
The easiest way to find out is to run 85 and see if you hear it pinging. Unless you have a loud exhaust, you'll hear it if it happens. It's not like our trucks have much firewall sound deadening, and a tank of fuel isn't going to hurt anything. Don't make it harder than it needs to be, and with as expensive as your fuel bill will be with that engine, it is definitely worth trying the cheap stuff.
Yes, cylinder pressure is lower at altitude. That's why you have 85 and most of the country doesn't drop below 87. Especially with the cold weather in the middle of winter, risk is low. It's not like a TBI 454 is the pinnacle of performance-tuned engines pushing limits on CR or timing. I doubt you'll have a problem unless you have some other issue with your engine (distributor, plugs, carbon deposit-incited hot spots on the piston crown, weak fuel pump that can't keep up with demand, etc).
Lower octane fuel is more volatile, higher octane is less so which is what gives it a bit more predetonation resistance. I've had a few older cars (notably '70s and early 80s BMW stuff) that actually ran better on lower octane fuel, presumably because the ignition systems were weak enough that the lower activation energy actually helped combustion. I could definitely see a TBI engine falling into the category of engines that benefits from fuel volatility.
Yes, cylinder pressure is lower at altitude. That's why you have 85 and most of the country doesn't drop below 87. Especially with the cold weather in the middle of winter, risk is low. It's not like a TBI 454 is the pinnacle of performance-tuned engines pushing limits on CR or timing. I doubt you'll have a problem unless you have some other issue with your engine (distributor, plugs, carbon deposit-incited hot spots on the piston crown, weak fuel pump that can't keep up with demand, etc).
Lower octane fuel is more volatile, higher octane is less so which is what gives it a bit more predetonation resistance. I've had a few older cars (notably '70s and early 80s BMW stuff) that actually ran better on lower octane fuel, presumably because the ignition systems were weak enough that the lower activation energy actually helped combustion. I could definitely see a TBI engine falling into the category of engines that benefits from fuel volatility.