Most any hobbyist familiar with engine tuning can relate to the usefulness of an inductive timing light. It consists of a strobe that's triggered by the electrical impulses passing through a spark-plug wire. As the strobe illuminates upon cylinder firing, it makes an otherwise variable Top Dead Center (TDC) mark on the harmonic balancer appear fixed, allowing the operator to compare it to a series of graduated stationary marks on the front cover, to measure spark timing.
As engine speed increases and the distributor advances, the balancer's variable mark follows and at some point can't be referenced to the stationary marks. In order to measure spark lead at all times, some hobbyists have modified their Pontiac's original harmonic balancer, adding one or several degree marks to it, while others simply purchase an aftermarket balancer that's completely indexed. Spark lead can then be determined when the appropriate variable degree mark reaches the stationary marks of the front cover.
Though these methods work well, it may not be convenient for some hobbyists to remove and modify their Pontiac's original harmonic balancer or lay out cash for a fully indexed aftermarket unit. Others may want to simply verify the accuracy of their modified original or check a new balancer's correctness. In these instances and many more, an adjustable timing light can prove an invaluable resource for any tuner. It uses an internal microprocessor to delay the strobe a selected degree, realigning the variable TDC mark on the balancer with the front cover's stationary marks.
The accuracy of the various adjustable timing lights presently on the market can range from poor to superb, and retail price isn't necessarily a separating factor. Since such a light might be used to tune a high-dollar engine, precise accuracy is required--even the slightest variance could lead to engine failure from full-throttle detonation. We routinely verify the accuracy of our adjustable timing lights using an engine with a fully indexed harmonic balancer and suggest the same to our readers.
Follow along as we provide six common uses for an adjustable timing light using Actron's No. CP7529 Digital unit. After connecting the clips of its power cables to the corresponding terminals of a 12-volt battery and clamping the inductive pickup to the No. 1 plug wire, taking all appropriate safety precautions, we started our Pontiac and let it warm to normal operating temperature. We then disconnected the vacuum advance canister, plugged its source, and got to work.
 Digital Timing Light No. CP7529...  Digital Timing Light No. CP7529 from Actron in Cleveland, Ohio, retails for about $115 and contains several features that make it a useful tool to any tuner. It boasts a digital LED display that shows engine speed up to 9,999 rpm and spark timing that's fully adjustable to 0.1 degree at the push of a button. We've found its calibration to be very accurate, and, according to Actron, its digital software is specifically designed to work with many popular DIS-type ignition systems like those from MSD. |  The harmonic balancer Pontiac...  The harmonic balancer Pontiac originally installed onto its engines features a single mark (variable), and it denotes TDC of the No. 1 cylinder when it aligns with the stationary "0" mark on the front cover. |  A conventional timing light...  A conventional timing light can measure spark timing only as far as the stationary marks cast into the front cover will allow. This particular photo shows a setting of 12 degrees BTDC. |
 Aftermarket harmonic balancers...  Aftermarket harmonic balancers like this unit from Powerbond are indexed and contain myriad degree marks. Such marks can be added to an original Pontiac balancer with careful measurement. An adjustable timing light can be used to periodically crosscheck accuracy. |  Base Timing Basics Though...  Base Timing Basics
Though an adjustable timing light isn't necessary to set most stock engines' base timing to the manufacturers' suggested setting, some modified street or race engines can require a spark lead setting that's outside the front cover's stationary range. An adjustable timing light can be used to set base timing to virtually any reasonable point. Simply unplug the vacuum advance unit, adjust the timing light to the desired initial setting, and rotate the distributor until the balancer's variable TDC mark is aligned with the stationary TDC mark (0) on the front cover. |  Total Timing Triumph Depending...  Total Timing Triumph
Depending upon the type of cylinder head being used, it seems that most Pontiac engines built today run best with total spark lead between 30 and 40 degrees. Verifying that amount can be difficult if an engine is equipped with its original Pontiac harmonic balancer, which isn't indexed beyond TDC. If that's the case, an adjustable timing light can make quick work of the task.The process is as simple as revving the engine until the variable TDC mark quits advancing and then turning the timing-light adjustment until that mark is aligned with the stationary TDC mark on the front cover. The amount shown on the dial or digital display is the current total spark lead setting. Also check to see at what rpm the advance stopped. A few passes down the dragstrip will help determine the amount of total spark lead your Pontiac runs best with. |