There are two LEDs inside...
There are two LEDs inside the interface module. The red one (LED2) shownwill light every time there is a trigger signal. The green LED (notshown) indicates the box is on and receiving power. The red LED iscritical in setting individual timing on a spin fixture. The circuitsare encased in a clear epoxy so there can be no fudging with thecircuitry.
The Zero-Cross distributor is designed for full-on racing applicationsand has some interesting performance features besides the individualcylinder timing control. The housing is CNC machined aluminum billet anduses a sintered bushing at the housing's bottom and a precision1.587-inch instrument grade bearing at its top to accurately locate thedistributor shaft at all rpm.
The Zero-Cross distributor has redundant ignition pickups stacked atopeach other so you can switch from a primary to secondary ignitioncontrol unit while retaining the custom cylinder-to-cylinder timing(unlike the situation that would occur if the primary and secondarypickups were wired 180-degrees apart). The secondary pickup is alsoadjustable. You can set it to take out two degrees of ignition timing,for example, from all of the individually-timed cylinders when youswitch to the back-up ignition. If you're wondering why you'd do this,one possibility might be reducing the overall engine output late in arace when the track is all greasy, which would help keep the tireshooked up. You could think of it as a sort of mechanically-governedtraction assistance.
An overhead view of the mounted...
An overhead view of the mounted Zero-Cross with the cap and rotorremoved.
There is no centrifugal or vacuum ignition timing advance in this racingpart. The distributor requires an interface control box for each of thetwo pickups to condition its uniquely stable trigger signal so it canactivate current MSD ignition controls and maintain complete redundancy.
Available for Chevrolet, Ford, and Chrysler V-8 engines, the Zero-Crosshas made its way legally into the Winston Cup Series and can be found onmany race-winning teams. It has been seen in some top dirt Late Modelsas well as DIRT Modifieds in action in 2003.
The distributor is designed to be rebuilt and teams can do their ownmaintenance and repair. MSD offers replacement/repair kits for theentire distributor.
Tucked inside a Chevrolet...
Tucked inside a Chevrolet engine, it's hard to tell what your opponent'srunning (another advantage to the distributor at the back of theengine). This Zero-Cross fit very nicely in an engine at the HendrickMotorsports shop.
Part Numbers
Chevrolet Distributor - 83971
Ford 351W Distributor - 83951
Chrysler R5 Distributor - 85911
Interface Control Box - 83581
(Editor's Note: Special thanks to Hendrick Motorsports and DaleEarnhardt Inc. for help on this story.)