Spark plug gap and engine pinging

[badillo347]

What spark plug gap do y’all recommend for my 347 running stock f150 ignition system, currently running some motor crafts coppers at .50 on 86 octane, timing set at 20 just like instructions and yes it was set at tdc by mechanic when motor was built engine does ping when giving full throttle on freeway as it tries to go out of 4th to a lower gear

[Stinger]

Plug gap and pinging are independent. 86 octane fuel is the issue as a fuel's octane rating is directly related to its resistance to preignition. If that's what you're going to run, adjust the timing advance table so it's got less advance where it's pinging.