Vintage Cars: 69 GTO Timing, deg btdc, vacuum advance

Question
Don,

I ahve a 69 GTO, 400, Q-Jet, TH 400, with an RAIII cam in it.  Base timing for the YS motor is 6 deg BTDC.  The RAIII setting is 12 deg BTDC.  Any suggestions as to where my timing should be set?

Regards,
Bill

Answer
The amount of advance would be determined by the type of cam and valve train more than anything, with compression ratio also taken into account.  So since you have the RAIII cam, I would try that setting first.  With the fuels we have today not meeting high compression specifications for engines from the 60's (todays high compression engines have computer controlled advance with knock sensors so they can run high advance with safety, your GTO has no such safety margin)

You may have to dial back the advance to prevent pre-ignition or spark knock.  Remember that if you can hear knock, there is usually more there than can be heard, so when you dial it back, go to where there is no knock and maybe take out another degree to be safe.

Also make sure your vacuum advance and mechanical advance in the distributor are working properly.

Don