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“Who cares about timing lights? I’ve timed the engine in my racecar a thousand times.....it runs the number.....it doesn't sound like it's detonating....what more do I need to know...?”
There's no question that timing lights are anvil-basic devices and are easy to use, but contrary to what you might first think, all timing lights are not created equal. Before we get into lights, think about this: The idea behind setting initial timing is to synchronize the firing "point" of the ignition with the position of the piston in the cylinder bore. In order to establish this synchronization, you use a timing light to determine piston position relevant to a number of degrees marked on either the harmonic damper or the timing tab. The only real problem with setting up timing in this manner is the fact that your timing equipment must be absolutely accurate. We should also point out that correctly indexed harmonic dampers as well as properly indexed timing tabs are crucial.
While it might come as a surprise to most serious racers, some (no, make that many) timing lights are not accurate! The reasons are varied, but in the majority of cases, timing lights have been designed for use in “more pedestrian, Mom and Pop” applications. Most tune-ups (professional and otherwise) seldom if ever require that the timing be checked beyond 2,000 RPM. As a consequence, many timing light manufacturers are able to construct a very simple, cost effective timing light.
And the key here is "cost effective". In some instances, a trigger delay is installed in the light (this practice is even found in some very high dollar “professional name brand” lights. I won't name them. Just think mega bucks). This has little effect in the lower engine speed ranges, but once the RPM level goes over the 2,000-RPM range, timing lights with delay circuits appear retarded. Another real problem is radio frequency noise protection. Most home-use timing lights have little if any protection against RF noise and as a result, can produce erroneous readings when used in conjunction with solid core wire sets.
According to MSD research certain types of timing lights with built-in adjusting mechanisms (usually the common “dial back” models) have been proven to be so inaccurate that they produce false readings at speeds in excess of several hundred RPM. Many of these adjustable timing lights also carry very high price tags. Before you purchase such a unit, compare it to a known timing light.
So what if your timing light is off a degree or two at 2,500 RPM? While it might sound like a small amount, keep in mind that whatever error exists in the light at low engine speed levels will be multiplied as the engine speed increases. If the light is off by two degrees at 2,500 RPM, it might be off by six or eight degrees at 6,500 RPM -- and as you can imagine, that happens to be a significant amount of error.
To determine the accuracy of your particular timing light, it should be checked against a digital engine analyzer at speeds below 2,500 RPM. Be certain that your light is installed properly (see below). Unfortunately, you can’t trust all digital analysis equipment over the 2,500-RPM ceiling.
Autotronic Controls Corporation (makers of the MSD ignition systems) recognized this problem and began to test a rather large number of available timing lights. Through this testing, they decided to develop their own timing light (P/N 8990). Additionally, this testing also revealed that an older model Sears Craftsman Timing Light (P/N A-2134) was considered very reliable and accurate. Both lights are stable and accurate from zero to 8,000 RPM and because of this, they are well suited to a modified (as in “high performance super rod”) application.
We’ve had the opportunity to test these lamps against several well know "professional" models and we found that a few of the other lights were showing much different timing at engine speeds slightly over 1,200 RPM. At the same time, the MSD light and the Sears light were virtually identical in performance. And yes, these two lamps compared favorably with a digital engine analyzer below 2,500 RPM.
There’s more to timing lights too. In truth, many enthusiasts (and believe it or not, that includes many of us in the high performance community) hook up timing lights incorrectly. It sounds bizarre but it isn't. Often, a convoluted header configuration coupled with a tight engine compartment will only allow one easy light installation. Trouble is, that installation might not be correct. If the timing light is setup incorrectly, the timing marks you are watching could be a mile (and more than a few degrees) off. According to MSD, when setting up your timing light, there are several things to consider:
• Be absolutely certain that the positive and negative clips are correctly attached to the battery or power source. Never use the coil as a source of power! Be certain that the pair of timing light power cables is not in contact or close to any of the spark plug wires.
• When connecting the trigger clamp to the number one cylinder, be absolutely positive that the clamp does not come in contact with any other spark plug wires. If contact is made or if the trigger is close to any other wires, there is a good chance that a false triggering will occur. Additionally, it is always a good idea to further separate the number one cylinder wire lead from any other cylinder wires. Stray signals or spark crossover will not influence the timing light if this practice is always followed.
• Some timing lights require the trigger clamp to be mounted in a specific direction on the spark plug wire. Be absolutely positive that your clamp is mounted with the jaws pointing in the proper direction. In the event that the clamp is installed upside down (and it's very easy to do), the timing will appear retarded.
As you can easily see, there's much more to timing lights than simply hooking up the power cables and clamping the inductive pickup over number one cylinder. Who knows, there's a chance you could find some serious power lurking in your engine. And only because you were fooled by a faulty timing light.
Both timing light power cables should be affixed to the battery. In the event that your car has a trunk mount battery or pair of batteries, add a power junction block to an accessible location in the engine compartment. Never use the coil as a source of timing light power.
Number One ignition wire must be well separated from the other wires on the engine. Spark cross over from other wires can easily influence timing light performance.
Be positive that the inductive pickup clamp is correctly oriented. Virtually all timing light clamps have arrows or instructions which indicate the proper orientation. If the clamp is installed backward, then the engine timing will appear retarded.
Never allow the trigger clamp to come in contact with any of the other spark plug wires. If the trigger clamp or the wire that connects to the clamp are close to spark plug wires other than number one, they can influence the timing. Similarly, the power wires can pickup false signals if they run too close to the primary ignition wires.
Autotronic Controls Corp. (MSD)
1490 Henry Brennan Drive
El Paso, TX 79936