Here is the first-rate advice of the "Mopar Engines: Speed Secrets, etc." book under the heading "Ignition tuning for Maximum Performance."  Every Interceptor owner should inscribe these words, as Homer says, "epi deltois kardiou."


"Tuning for maximum performance assumes the rest of the engine is also suitable for maximum performance.  The octane rating of the fuel being used must be sufficient to accommodate the engine's compression ratio.  The engine harmonic balancer must have either degree marks or a timing tape which shows up to 60 degrees before top dead center.  [Or you must use a timing light on which degrees of advance can be read.]  The carburetor must be jetted so that detonation or surging is not caused by the fuel mixture being too lean when the ignition is at maximum advance.  The ignition coil and spark plug wires must be able to deliver sufficient spark to fire the plug under maximum engine loading.


"If the procedures outlined for maximum performance are followed and the engine begins to detonate, you must decrease the timing advances until the detonation is eliminated.


"Tools Required:  Timing light, 3/32'" allen wrench, vacuum gauge with long hose, and a friend or helper.


1.  Set the basic timing for total mechanical spark advance.

a)    Disconnect and plug the vacuum advance hose.

b)    Connect timing light to the battery and number 1 spark plug wire.

c)    Loosen the distributor hold-down clamp so the distributor housing may be rotated by hand.

d)    Start the engine and allow it to warm up fully.

e)    Set the idle speed to 2600 rpm.

f)    Set the timing to 32 degrees BTDC.

g)    Tighten the distributor hold-down bolt.

h)    Reduce the idle to the original setting, unplug and reconnect the vacuum line.

2. Set the vacuum advance for total ignition advance.

a)    After the basic timing has been set for total mechanical spark advance, disconnect the vacuum advance hose at the carburetor.  Connect a vacuum gauge to the carburetor's vacuum advance port and route the gauge and hose into the passenger compartment.  Place the gauge in a location that an assistant can read while the vehicle is being operated.

b)    With the vehicle in operation, note the maximum amount of vacuum generated by the engine while in gear and being held at a steady speed between 2000 and 4000 rpm.

c)    Stop the vehicle, turn off the engine and connect a timing light to the battery and number 1 spark plug wire.

d)    Start the engine and raise the idle speed to 2600 rpm. Connect a vacuum source to the distributor's vacuum canister and draw vacuum up to the reading noted in step b.

e)    Note the total advance shown on the harmonic balancer.

f)    Total advance, mechanical plus vacuum, should be 52 degrees. Disconnect the vacuum source and insert the allen wrench into the internal vacuum canister adjusting screw. Turn the allen screw (clockwise to decrease, counterclockwise to increase) to obtain 52 degrees.  Reconnect the vacuum source and recheck the timing. Continue repeating this procedure until 52 degrees is reached.

g)    Remove the timing light and vacuum source.  Reconnect the vacuum advance hose.  Reset the idle speed to your original setting."


If all this seems overwhelming to your professional tuning guy, Derek, tell him simply to set the timing to 10 or 12 degrees BTDC and have done with it.




David Crowne in San Diego

71 Interceptor III 133/5474 (with ignition timing set for maximum performance)