| Essentially, a multi-cylinder engine is a collection of | | | | wheels") for their racing ignition distributors. They |
| individual engines operating at different combustion | | | | were machined with a few degrees of advance |
| and mechanical efficiencies. If we can optimize the | | | | or retard built into each reluctor arm. This |
| power output from each one, the overall total | | | | machining practice is much more common today. |
| power will increase. | | | | The reluctor arms are angled a few degrees |
| When the typical multi-cylinder engine's ignition | | | | (typically between two and four) off their normal |
| timing is tuned through a distributor, it is being set | | | | axis (every 45 degrees in a V-8) to advance or |
| at a compromised value that is the most total | | | | retard the ignition timing trigger signal per cylinder. |
| ignition timing allowed by the weakest (defined by | | | | Some racers without such precise machining |
| its engine knock limit) of the individual cylinders. | | | | abilities have approximated the same result by |
| For example, if the number two cylinder of a | | | | gingerly bending the trigger arms or filing their |
| Chevy V-8 only tolerates 29 degrees BTDC | | | | leading edges. These custom-modified reluctors |
| (before top dead center) of total ignition timing | | | | are installed and engine output is dyno measured; |
| before damaging engine knock in that cylinder | | | | eventually, the best staggered timing is achieved |
| begins, we have to set a conventional ignition | | | | for a specific engine combination. |
| distributor to that overall value of ignition advance | | | | Staggered ignition timing makes for interesting |
| for all of the other cylinders. We could be giving | | | | reading from a timing light: cylinder 1 might indicate |
| up power gains from those other cylinders that | | | | 29 degrees BTDC, but cylinder 7 might show 33 |
| could tolerate more total ignition advance, say up | | | | degrees BTDC, to use a broad example. Plus, if a |
| to 32 degrees BTDC. | | | | distributor had been modified for staggered timing, |
| Staggered Timing | | | | you want to make sure it is clearly marked as |
| Back in 1992, General Motors Racing, Richard | | | | such, so that it doesn't get installed, or timed in an |
| Childress Racing, and Hendrick Motorsports | | | | engine not built for it. Broken parts can result. |
| experimented on the engine dyno, retarding the | | | | Aftermarket electronic ignitions have progressed |
| ignition timing of cylinders 1, 2, 7, and 8, and | | | | quite a bit since 1992. You can now buy retrofit |
| advancing it in the remaining cylinders of a | | | | digital ignition systems that permit ignition timing |
| restrictor plate Chevy V-8 Winston Cup engine. | | | | curve programming via a laptop. Unfortunately, |
| (They also experimented then with building | | | | most stock car racing series still don't allow such |
| engines with different static compression ratios in | | | | digital manipulation of ignition timing. However, you |
| individual cylinders, but that's a topic for another | | | | can now find a mechanical equivalent as MSD is |
| time.) By using real time combustion pressure | | | | offering the Zero-Cross Pro Billet distributor. |
| analysis of each cylinder (which was advanced | | | | This racing ignition distributor allows you to adjust |
| test measuring at the time, but now regularly | | | | the ignition timing for separate cylinders by |
| done at top-line Cup shops), they determined this | | | | incorporating a reluctor assembly with eight |
| "staggered ignition timing" resulted in net torque | | | | individual magnetic trigger arms that can be |
| gains and reduced the average engine stress in | | | | advanced or retarded as needed. They can be |
| knocking cylinders by 25 percent and peak stress | | | | adjusted 0-6 degrees of crankshaft timing. No |
| by 19 percent. Taking this positive power result | | | | laptop is needed, just a feeler gauge. |
| off the dyno and onto the track would seem | | | | Cleverly enough, this individual cylinder timing |
| straightforward--mechanically modify the ignition | | | | control is packaged in the race-proven billet |
| distributor triggering to advance or retard the | | | | housing and uses a large cap and rotor assembly, |
| timing in each cylinder by just a few degrees. | | | | so it's not directly obvious that you're running a |
| Remember, no digital ignition control of ignition | | | | distributor that has such adjustable timing precision |
| timing was (or is) allowed in many racing series. | | | | inside. You don't have to set a fixed, |
| Top Winston Cup teams began to use their | | | | compromised ignition timing for all the cylinders, |
| impressive CNC machining centers to cut | | | | but can individually manage timing in each cylinder |
| custom-designed magnetic pickup triggering | | | | for best output before engine knock occurs. |
| reluctors (also called "star wheels" or "paddle | | | | |