91 Octane in a 340?

trivium91 said
Im wondering if I can run 91 octane, so far I've just been running 94 but it's expensive and harder to find in my area. The engine is mostly stock from what I understand, so 10.5: 1 pistons pre 1971 with X heads. Though im not sure of the cam but I believe it's a COMP XE284 high lift but might be XE268 aswell. I have a Edelbrock AVS2 800 Carb I believe aswell. I just checked the timing and its set at about 33 degrees @2500RPM. The cam definitely has more duration than stock though and it's lumpy at idle. Would a cam with a longer duration bleed off more cylinder pressure and allow advanced timing or lower octane gas, or am I not understanding something?

Given the fact that these stock 340's were underrated in the power, I've heard that the stock 275HP was rated at a lower RPM and the actual power was actually around 330hp. Regardless, these engines came with 10.5:1 compression from the factory according to specs, what octane were these cars running with from the factory? I can't imagine it was over 91.

What does engine pinging/knocking feel like? Just a temporary loss of power for a split second, or similar to a misfire?

You need to watch a Youtube by GT 350 Garage. Yes, I know he focuses on Ford, but he does a couple of tuning posts that are applicable across the board. One involves timing and advance curves and the other discusses at length fuels, modern fuels as compared to the muscle car era leaded fuels. He gets into oxygenated fuels and air/fuel ratios.
Pinging or spark knock is nnot really felt, it is heard. The 390 Ford 2V was supposed to run on regular fuel. They had a tendency to rattle twice coming off a street light. Sounds a bit like marbles in a can. In those 390's that is the limit on spark advance coming off idle and will not harm the engine. Now under cruise or full throttle for a longer time, yes the engine will be damaged.
The 390 4V requires a bit of 91 to control spark knock. I found 40 years ago that about $5 when filling up was enough. Now that is likely $20.
Modern fuels vaporize easier and combustion is cooler. The ethanol in the gasoline may be corrosive to old carburetor and fuel pump parts.
The ethanol changes the stoiciometric or Lambda fuel ratio. On the old fuels prior to ethanol, the air/fuel ratio for complete combustion was accepted as 14.7:1 With 10% ethanol, that is now about 14.1:1. The GT350 Garage video does a good job explaining this.
I am changing my Performer 600 primary boosters to the AVS2 650 annular boosters for fuel atomization on the Airgap manifold. Edelbrock Tech recommended starting with the AVS2 calibration, which appears to be richer. I did not understand this until watching this video. When I am able to assemble and install the engine, I will get a wide band 02 monitor to verify the fuel calibration. The distributor advance will need to be adjusted also.