Advance the timing before TDC. Why?
The goal at idle is maximum power efficiency. With an automatic transmission, the engine should hardly lose any rpm or vacuum when placed in gear. Timing and Fuel Work Together
Here's an example of a 318 clean air system timing (from a shop manual) that had an initial of TDC at 725 rpm..
Notice how fast it advances from 750 to 950 rpm. This was to make up for the fact it was purposely retarded at idle to make the cylinders hotter and more completely consume the hydrocarbons. But no way to know what the curve looks like unless you measure it. Well if the tag is still on the distributer, then the shop manual will have the specs. So that is a way to get an idea of the advance without measuring.
The goal at idle is maximum power efficiency. With an automatic transmission, the engine should hardly lose any rpm or vacuum when placed in gear. Timing and Fuel Work Together
Here's an example of a 318 clean air system timing (from a shop manual) that had an initial of TDC at 725 rpm..
Notice how fast it advances from 750 to 950 rpm. This was to make up for the fact it was purposely retarded at idle to make the cylinders hotter and more completely consume the hydrocarbons. But no way to know what the curve looks like unless you measure it. Well if the tag is still on the distributer, then the shop manual will have the specs. So that is a way to get an idea of the advance without measuring.
