Pinging on acceleration.
750 rpm TDC
800 rpm TDC
1000 rpm 6* BTC
1200 rpm 10* BTC
1400 rpm 14*
1600 rpm 18*
1800 rpm 21*
2200 rpm 23*
2800 rpm 24* BTC
Plotting those on the graph, the timing looks the original '73 advance. Circles joined by heavy line.
Now lets turn distributor so the initial is now at 5* BTDC.
The entire timing curve shifts 5 degrees.
At 2600 rpm, instead of 24* the timing is 29*BTC.
That's 3* more than the factory spec for '67, and 5* more than the spec for 73. Would not be surprised if it pings, especially once the engine got heat soaked (long drive or steep uphills).
Lets say you set the timing at TDC and measure the following:
750 rpm TDC
800 rpm TDC
1000 rpm 6* BTC
1200 rpm 10* BTC
1400 rpm 14*
1600 rpm 18*
1800 rpm 21*
2200 rpm 23*
2800 rpm 24* BTC
Plotting those on the graph, the timing looks the original '73 advance. Circles joined by heavy line.
Now lets turn distributor so the initial is now at 5* BTDC.
The entire timing curve shifts 5 degrees.
At 2600 rpm, instead of 24* the timing is 29*BTC.
That's 3* more than the factory spec for '67, and 5* more than the spec for 73. Would not be surprised if it pings, especially once the engine got heat soaked (long drive or steep uphills).