The crank-trigger system is deceptively simple-just a timing wheel with four magnets epoxi
Imagine for a minute that, as a dirt racer, you have the ability to dial down your engine's power output as the track loses traction. Sounds a lot like traction control, right? Well, sort of. You can do this by running a dual ignition system on your engine, but that's not the only advantage.
There's a reason most modern engines use a crank-trigger ignition. Timing the spark off the crankshaft location is one of the most precise methods available. The more traditional method of timing the spark off of the camshaft adds many more opportunities for timing errors. Consider the mechanical steps required before a spark can fire the incoming air/fuel charge: The crankshaft is used to turn the camshaft via means of a timing chain, which can stretch over time. The cam, which is spun by the timing chain on one end and spins the timing gear on the other, is subject to deflection when used in high-rpm applications in conjunction with strong valve springs. That scenario is more common in stock car racing than anywhere else. Timing can also be adversely affected if the camshaft isn't degreed properly. The cam spins the distributor shaft through a set of meshing gears, which wear over time. Finally, the rotor inside the distributor is subject to spark scatter at higher rpm levels.
The conventional distributor is still necessary because it routes the spark from the coil
Steady Spark Timing the ignition spark with a crank trigger is relatively easy. Several racing companies make kits, and the systems are typically legal in dirt Late Model and other types of racing. Clements Racing Engines pays the electricity bill by building all types of racing engines, but it does its best work in the no-holds-barred world of dirt Late Model racing. (The Clements organization was named the 2003 Engine Builder of the Year in the Southern All-Starts racing series.) For the past few seasons, Clements Racing Engines has been using crank-triggered ignition timing on its all-aluminum 800hp Late Model monster engines, and the devices have been so helpful that Clements now incorporates them in any engine package where the rules allow.
"There are several reasons why a crank trigger for the spark timing is an advantage," says Glenn Clements, one of the three brothers who run the company. "But the most important for us is how it calms the timing down. It just gets rid of all that monkey motion involved with running your timing off your distributor. It's not a big deal at lower rpm, but when you get into the rpm ranges that we are racing at, you can see the timing jump around by as much as 5 degrees.
Here's an early sign of damage: The wiring between the ignition box, and either the distri
"Before we started running the crank triggers, when we walked through the pits before a race, the question we were most often asked was, 'Can you come check my timing?' It wasn't that they didn't know how to use a timing light; they just weren't sure where to set the timing because it moved around. But now, with the crank trigger, the timing marks under a timing light look rock solid. That tells you a lot about how much more stable the spark is with a system that fires off the crank."
The triggering system itself is actually quite simple. Clements prefers a unit sold by Moroso. Others may differ slightly, but most work on the same premise. A timing wheel containing four evenly spaced magnets bolts to the front of the harmonic balancer. Then, a sensor is mounted on a bracket facing the outside edge of the wheel. Every time one of the four magnets passes the sensor, the sensor sends a signal to the ignition box to send out the spark. After amplification in the coil, the spark is sent to the distributor where it is routed to the correct plug. Because the crankshaft spins two full revolutions before all eight cylinders are fired, only four magnets are necessary in the wheel.
This, obviously, means that the distributor is still a necessity. It is no longer used to fire the spark, but it is necessary to route the energy to the correct cylinder to fire the compressed air/fuel charge. Clements says that when using the distributor for spark routing, perfect phasing isn't necessary.