91 Octane in a 340?

Rat Bastid said
Two things to remember.

1. There is absolutely ZERO reason to run less than 91 octane (or whatever the highest octane available in your area) ever. Low and mid grade fuels have far more fillers and junk in them than premium grade fuels do, and the regulations are much tighter for premium grade fuels.

Proclaiming one can run their stuff on 87 octane is a fools errand. The money you save is pissed away in less fuel efficiency and dirty combustion.

2. Most guys can run way more compression on pump gas than they think they can. You have to control some things but it’s not hard to do once you clear your mind of all the bullshit that gets pumped out in the media and on forums.

I have been running higher than orthodox compression ratios on pump gas since the mid 1980’s. It‘s crazy to piss away power and driveability from fear of detonation.

Idk, I put a decent amount of street miles on my car and there's a big price gap between regular and premium gas nowadays, close to a full dollar at some stations. When I put together the 360 in it now I didn't want to spend the money to swap out the stock 5.9L Magnum pistons and hone the cylinders for new pistons and rings. With Edelbrock open-chamber heads, .027" Cometic head gaskets and stock pistons (shallow dish) .050" down at TDC my static compression is right at 9:1. I've run only regular gas in this engine since I installed it in the car and it's going on 5 years now with about 10,000 miles. I've accidentally had the ignition advance as high as 44 degrees initial+mechanical (at 5000' elevation) and it never pinged, just made slightly less power than when I backed it down to 40. Since moving to sea level it's now at 36 degrees total, not including vacuum advance. I know premium fuel is "cleaner" but I also run a few ounces of Lucas ethanol fuel treatment with every fillup and the car never sits for more than 2 weeks without being driven. I had the carb off the intake yesterday and the plenum looks spotless, no varnish or any weird stuff. Inside of carb is clean too, it's only the outside where some raw fuel spilled and then slowly dried where there's some yellow/brown varnish residue.