![]() ![]() Tuning the static or initial timing is achieved by simply twisting the distributor body in relation to the rotor. Static timing can vary from as little as 8 degrees before TDC to over 40 degrees depending upon the engine. ![]() When you combine static or initial timing with progressive timing the result is total timing. The two elements of ignition timing: static or initial timing and progressive timing Firing before TDC is necessary because of the time it takes for the flame front to ignite the air-fuel mixture in the cylinder. Furthermore, the ignition is always timed to fire the spark plug before the piston reaches Top Dead Center (TDC) in the cylinder. Ignition timing is affected by a host of elements including fuel type, mixture strength, combustion chamber shape, compression ratio, temperature and humidity. As the rotor spins, the current jumps across the tiny gap to each of the small metal tabs, completing the electrical circuit and sending short-duration, high-voltage currents to each spark plug on time. The rotor is connected through the high-voltage coil to the battery, and the small metal tabs in the distributor cap are connected via spark plug wires to the spark plugs. A condenser has the dual function of extending the life of the points by quenching the arc across the points and forming a resonant circuit with the coil that boosts peak voltage. ![]() A rotor mounted on the upper end of the mechanical cam and functioning within the distributor cap routes the high-voltage impulses to the correct spark plug. Inside the cap there are small metal tabs, one to serve each spark plug. The high voltage was delivered from the coil to the center of the distributor cap via a high-voltage wire. The points switched electrical current to the coil which converted it to high voltage required to fire spark plugs. An engine-driven mechanical cam in the distributor rotating at camshaft speed operated a set of breaker points. A distributor was employed to determine when each spark plug should fire. background on points-and-coil ignitionīefore sophisticated electronic management systems arrived, we used the points-and-coil ignition system that first appeared on the 1910 Cadillac. They require no fancy equipment or computer knowledge, often just a timing light, a screwdriver and a few wrenches. ![]() And, ironically, older vehicles can be simpler to tune. Still, what a joy it is to understand the psychology of the hot rodder who lusts for a carburetor and a distributor. Where there was once a distributor, multiple coils now exist, often one on each spark plug. They report to an ECU (engine control unit) that constantly ascertains all the variables and tells each spark plug when to fire. They sense Manifold Absolute Pressure, Mass Air Flow, crankshaft position and so on. High-performance carburetors, intake manifolds, cylinder heads, camshafts, and other tuning components are all dependent upon correct ignition timing if the spark is not delivered at the proper time to the combustion chamber, the quest for optimum power or economy is impaired.īut the distributor has vanished! Tuning contemporary hot rods involves electronics and computer software. There is a cardinal rule of carburetor tuning: “Ignition first.” Once the static ignition setting and the ignition advancing mechanism in the distributor is correct, the air-fuel mixture can be tuned for full power and fuel efficiency. Story and Photographs Courtesy: Moore Good Ink ![]()
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