Setting the timing with a crank trigger is much the same as before. You use a timing light to check the timing, but instead of turning the distributor to adjust the timing, you move the sensor in relation to the wheel. Because the crank is spinning clockwise, moving the sensor higher toward the 12 o'clock position (assuming the sensor is mounted on the left side of the timing wheel) will retard the timing. Conversely, moving the sensor closer to six o'clock will advance the timing.

Managing Wheel Spin Just because a crank trigger assembly is mounted to the front of the engine doesn't mean the distributor can't also be used. Smart racers can actually use the cam-driven distributor as a backup timing device and switch between the two as a kind of poor man's traction control. For this setup, Clements recommends setting up the crank trigger at the optimum timing and retarding the distributor timing approximately 4 degrees from that mark.

Wire the ignition systems to a switch within the driver's reach, and then to the ignition box. If you are using a backup ignition box, use two switches-one to select the timing system, followed by a second to determine which ignition box will be hot. After the ignition box, the rest is typical: A coil boosts the power, and the rotor routes the spark to the correct plug.

The result is that the crank trigger is the primary timing mechanism set for peak power. If racing on a dirt track, the driver has the option of switching over to the distributor timing, if the surface loses traction and wheelspin becomes a problem. Retarding the timing 4 degrees typically cuts the engine's power approximately 5 percent. It's not too much to make the car uncompetitive, but enough to help the driver control wheelspin when exiting the turns. Plus, because the distributor timing is used when peak power isn't the goal, a little timing flutter isn't a big deal.

Wire It Right
Although the crank trigger timing system is dead simple, Glenn Clements cautions that one of the most common-and most costly-errors he sees is bad wiring on the electrical system. This is true no matter which ignition system is used. Many racers cut off the stock connectors on their MSD systems and install weatherpack connectors in order to prevent water intrusion when washing the race car. The only problem with this is MSD wiring can be a little confusing. When using the original equipment connectors, it's impossible to plug in the wires backwards, but when the wires are cut and respliced into the weatherpacks, it's very easy to get things confused. In MSD systems, the violet-and-black wire connects to the green wire-not the violet wire, as you might expect.

Adding the extra component of the crank-trigger ignition only adds more wires to the equation. If the wires are reversed, the ignition can fire as much as 60 degrees before top dead center (BTDC), which means severe detonation. Clements says they can even adjust the timing so that everything looks right according to the timing light, but the spark will still be dangerously advanced. Once the car is on the track, it can take as little as three hot laps to turn the thing into scrap metal. Almost every time, the first area damaged is the side of the top of the piston where the intake valve pocket is closest to the ring land (because the spark is firing while the valve is still open). After this area cracks and breaks, things quickly go downhill, and the parts bill starts adding up fast.

Fortunately, it's a simple matter to make sure this doesn't happen to you. When using a dual timing setup, Clements has an easy procedure list to make sure everything is in working order. First, double-check the wiring. On MSD systems, the violet wire coming out of the ignition box connects to the orange wire. Connect the green wire coming out of the ignition box to the black wire coming out of the trigger sensor.