by Hib Halverson
© December 2012
Robust ignition goes hand-in-hand with properly calibrated, high-performance carburetion. Firing lean AFRs at part-throttle with minimal misfire as well as being able to perform at 6500-rpm can be a tough test of an ignition system.Before taking on the Double-Pumper tuning challenge, make sure your ignition is up to snuff. This means plugs, wires, cap, rotor, distributor and coil. Not only must your ignition system be in good condition but the hardware should be engineered for high-performance use. Lastly, make sure your spark advance curve is selected for a high-performance, street duty cycle and adjusted properly. If you don't address these issues before a carb tuning session, some of what you do will be wasted effort.
I was part-way into tuning my 850 when I found some of the ignition pieces I'd had on the Big-Block from Hell for years were no longer getting the job done. My, distributor an old L88 ball-bearing, tach-drive unit, was diagnosed with a weak trigger signal, so I pitched the offending spark-sorter for a new MSD Pro-Billet unit (PN 8572). MSD's distributors incorporate some of the technology MSD developed for NASCAR racing. The distributor body is billet aluminum. Its half-inch shaft rides on a ball bearing and a sintered bronze bushing. It uses the proven MSD magnetic-trigger assembly and has an adjustable mechanical advance assembly. I added an MSD "Cap-A-Dapt" kit which converts the distributor to use a large-diameter, Ford cap and I installed one of MSD's adjustable rotors which allows changes in rotor phasing.
BBfH's original MSD-6T had been in service for 20 years. After two decades of trouble-free operation, it was time for an upgrade, so I picked one of the famed ignition maker's, new "Digital 6AL" ignitions. For the Digital 6AL, Autotronic Controls, maker of MSD products, designed a new housing with the same footprint as the previous 6AL (but slightly larger than the older 6A or 6T ignitions) but lowered its height. Wiring is now routed out one end of the unit through a sealed, locking connector. The rev limiter was moved to top of the housing for easy access to its rotary dials.
Inside the Digital 6 is a microprocessor that controls firing impulses and the rev limiter. The circuit design was updated and modern, more efficient components are used. Those changes enable the Digital 6AL make more power but draw less current. The Digital 6AL delivers over 530 volts to the coil with up to 135 millijoules of spark energy. It comes with the wiring harness and other components needed for installation. It's compatible with 12-volt, negative ground electrical systems. It can be triggered by breaker points or magnetic pickups though a mag trigger is preferred for best performance.
I screwed-in a fresh set of Denso ITF20 Iridium Power Spark plugs which I like for their Iridium, fine-wire center electrode. Finally, I installed new MSD Super Conductor spark plug wires. The existing Super Conductors passed a resistance test, but one of the plug boots was damaged-no doubt from about 20 years of spark plug changes-so I put on new ones.
After an ignition revamp, my problems with consistent spark were solved.