Despite what you may think,...
Despite what you may think, there's more to distributor tuning than simply setting the ignition timing. This month, we'll show you how you can make more power by changing the advance curves in your distributor.
The main purpose of the distributor in your engine is pretty much self-explanatory. In basic terms, it distributes the high-voltage energy of the coil through the spark plug wires to the spark plugs, igniting the mixture in the combustion chamber. While this function seems pretty straightforward, the distributor is actually more complicated than most people realize. Whether your distributor is an older breaker-points-style unit, a factory electronic ignition distributor, or an aftermarket piece, it contains internal springs and cams, which work together with centrifugal force to alter ignition timing for different engine speeds. The rate at which the distributor alters ignition timing is known as the "advance curve" of the distributor. This month, we'll show how you can use the distributor's provisions to change the advance curve, improving the power and torque your engine makes.
Most factory Mopar distributors were designed for a compromise between power, economy, and emissions. The advance curve of factory distributors generally starts at low initial ignition timing for easy engine starts. Then as the engine rpm increases, a combination of weights and springs inside the distributor add more ignition timing to the engine. Additionally, a vacuum-actuated control will adjust the ignition timing for part-throttle settings, helping improve economy and reduce emissions. The problem with the advance curve of most factory distributors is that it's too slow to advance the timing for a performance engine, and not enough ignition advance equals reduced power and torque. Even a mildly modified engine generally likes the timing to be fully advanced at around 2,500 rpm, and most distributors don't achieve full advance until 3,000 rpm or higher. Fortunately, changing the advance curves of most distributors simply involves taking the distributor apart and changing the internal advance springs.
Generally speaking, lighter advance springs will allow centrifugal force to advance the timing more quickly for better performance. When tuning a factory distributor, the optimal advance curve can either be achieved on a dyno, at the track, or a combination of both. A distributor machine is a nice tool to use if you can find a local shop that still has one. This machine will spin the distributor and plainly shows at what rpm the advance curve starts and ends, so changes can be made before the distributor is even in the car. Alternatively, most aftermarket distributors come with a variety of springs and a graph that will tell you which combination of springs will give the advance curve you desire. Either way, getting the distributor to advance the ignition timing more quickly than the factory unit did will almost certainly help your engine make more power.
To change the advance springs,...
To change the advance springs, the distributor must be partially disassembled, so the first step is to remove it from the car.
To remove the shaft and advance...
To remove the shaft and advance mechanism from a factory distributor, remove the lower bushing by pressing the roll pin out of the shaft. The distributor shaft can now be removed through the top of the distributor housing.
The advance springs are now...
The advance springs are now exposed and are easily removed with a small screwdriver so they can be replaced with lighter springs for better performance.
Lighter advance weight springs...
Lighter advance weight springs are available from Mopar Performance for just over ten bucks.
You can set the advance curves...
You can set the advance curves by trial and error using the tach and a timing light, but a distributor machine like this one makes the process easier. The key is to have as much initial advance as will allow the engine to start easily, and for the curve to provide full advance before 2,500 rpm (this rpm and degrees of total advance will vary depending on your combination).
Aftermarket distributors like...
Aftermarket distributors like this MSD unit are easy to work on and come with a variety of advance springs for multiple tuning options.
The weights and advance springs...
The weights and advance springs in the MSD distributor are located just under the rotor, so spring changes don't require disassembly of the distributor and can even be accomplished with the distributor in the engine.
The MSD distributor has all...
The MSD distributor has all the advance curve options clearly marked on the outside of the box. We've put MSD distributors on a distributor machine to check these curves and have found them to be spot-on, eliminating the need for a distributor machine for tuning.
With our advance curve set,...
With our advance curve set, we install our new distributor so we can do some track testing. Remember, changing the advance curve won't help a distributor that has worn bushings, burned points, or a bad pick-up coil, but it is an inexpensive way to improve engine performance.