383 Timing. TDC versus 36 degrees

[Racer57]

Why is factory spec TDC ?

[DeathProofCuda]

TDC initial timing spec for the 70 383 HP motor is for emissions control.  These engines were equipped from the factory with a solenoid on the distributor to retard the ignition timing at idle for better emissions at idle.

The best resource I've seen for how/why this was done is the Master Technicians Service Conference manuals put out by Chrysler back in the day.  Check out the link below.

https://www.mymopar.com/downloads/mtsc/270.pdf

[headejm]

TDC is factory spec for manual transmission. For automatic, spec is 2.5 BTDC. I just rebuilt my 1970 383 HP and installed a Lunati camshaft with good idle vacuum. My initial timing is 15 BTDC with an automatic.

[DeathProofCuda]

TDC is factory spec for manual transmission. For automatic, spec is 2.5 BTDC. I just rebuilt my 1970 383 HP and installed a Lunati camshaft with good idle vacuum. My initial timing is 15 BTDC with an automatic.

Yes, just to be clear, unless you are running a working factory original dizzy with the advance retard solenoid AND you are tuning for best emissions, instead of best performance, you should completely ignore the factory timing specifications.