Crane Cams’ Fred Husher

One of the more interesting seminars at this year’s AETC event was put on by Crane Cams’ Fred Husher, who discussed the importance of ignition timing accuracy and the causes, impacts, and solutions of inaccurate timing.

Ignition timing accuracy is more important than just about any other engine parameter; if the spark is not lighting off at the exact proper time, then the engine won’t perform to the expectation. According to Husher, assuming an engine is up to par and capable of ‘perfect’ performance, ignition system performance is limited by the cumulative errors in three specific areas: mechanical elements, sensors, and signal processing.

If ignition timing is retarded, acceleration is slowed, the engine can overheat as cooling system capacity is exceeded, and pre-ignition frequency rises as the engine’s temperature goes up. On the flip side, if timing is advanced beyond the correct specification, engine acceleration is aided, but the combustion chamber gases get hotter, which can lead to burned valves and pistons. In addition, piston and connecting rod stress will increase.

“You get unintended timing changes that will generally be highest during acceleration and de-acceleration, due to the mechanical backlash that occurs in between the distributor and the camshaft. There are also sensor signal processing errors, and predictive errors that occur inside the ignition control module,” says Husher.

He discussed the idea that within the engine there are interactive relationships between components that can mask what the real issue may be, noting the response time between sensors, signal processing delay, and other factors that can cause inaccurate time.

Possible Perpetrators:

• Engine mechanical tolerances to driving trigger sensor
• Trigger sensor behavior to its stimulus
• Trigger detector edge detection accuracy and repeatability
• Signal processing delay through ECU/ICU
• Managing spark gap between rotor and cap and the spark plug

Husher noted that mechanical causes are often the easiest to identify, as distributor shaft play, rotational wobble, and backlash between the cam and distributor gears can all create issues if not detected. Camshaft end play can cause the distributor to shift timing, while crankshaft torque can move the crankshaft trigger wheel or timing disk to also cause problems.

He also explained that electrical causes can be much more difficult to identify, as they are not easily measured using common tools. In this group are poor head ground return, insufficient current supply capacity to the ignition module, an overdriven ignition coil, and the distributor rotor contact shape, material, and surface finish.

From these causes, the seminar then turned to different styles of ignition triggers; variable reluctor coils, digital signals like Hall Effect and opto-interrupter sensors, RS-232, capacitor coupled outputs like the Crane Race Billet distributor, differential RC outputs (Crane crank sensor), and exotic signals like magnetorestrictive, piezoelectric, and Wiegant sensors were all covered.
Attributes of each style of sensor, its individual characteristics and how they can affect ignition timing, and potential pitfalls of each were covered. Husher covered Crane’s testing methods and the individual products the company offers in each type of ignition.

In closing, he explained that ignition triggering accuracy can be within .1 degree over all RPM if the correct trigger sensor, measurement site, trigger signal detector, and distributor are all within specifications. The seminar dove deep into electrical engineering concepts that there simply isn’t room to cover here, but this further reinforces that attendance at AETC is a great idea for engine builders, tuners, and enthusiasts alike. The concepts covered here are on a level you won’t find anywhere else.

All in all, a very informative seminar, showing just how intricate the relationship between ignition timing and overall engine performance relate to each another.