Adjusting ignition timing must be performed with a timing light with an accurate harmonic balancer. Be sure your harmonic balancer has its timing marks properly indexed. You’d be surprised how many times you get it wrong using a worn-out balancer or one improperly indexed from the factory. Even a new harmonic balancer must be checked for proper indexing. I’ve seen them as much as 11 degrees off, which causes a lot of confusion.
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Once you have established the balancer is properly indexed, you must find true TDC at cylinder number-1, which is midway in the crank rollover point for the crank journal (12 o’clock). Install and index the distributor at cylinder number- 1. This is called static timing, and where you begin tuning.
Be ready to set ignition timing right off the bat with the engine at 2,500 to 3,500 rpm. With the vacuum advance connected at 3,500 rpm, where is your ignition timing? Igniton timing should be checked two ways at 2,500 to 3,500 rpm: vacuum advance connected and disconnected. Total ignition timing with vacuum advance connected should be no more than 36 degrees BTDC. At idle, it should be 6 to 12 degrees BTDC.
When dialing in total timing, begin conservatively at 30 to 34 degrees BTDC and observe operation. Push it as far as 36 to 38 degrees BTDC, but no higher. Under hard acceleration or loaded on a dyno, listen for spark knock. If you have spark knock, retard ignition timing 1 degree at a time and try again.
When you’re checking ignition timing, you want to know total ignition timing (advance), and the rate of advance when the throttle is opened. When you goose the throttle, timing mark movement should roll with throttle movement. You want spark advance to roll quickly with RPM increase and throttle movement. If you don’t have a vacuum advance, spark advance should increase in linear fashion with RPM—more slowly. Ultimately, at 2,500 to 3,500 rpm, total timing should never be more than 36 degrees BTDC. Of course you can push it to 38 or even 40 degrees BTDC, but it is risky even if you don’t get spark knock.
Conditions change when it is hot and you’re roaring around a road course at wide-open throttle, which is when you can get pinging (spark knock) and not be able to hear it. That is when the damage is done. This is why you want to start out conservatively with ignition timing and change it 1 degree at a time.
Written by George Reid and Republished with Permission of CarTech Inc
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