“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.