This photo shows the elegant...
This photo shows the elegant simplicity of the quick and easy conversion. The tapered base simply fits down over the original diameter distributor, ready to accept the larger diameter cap. Of course a longer-than-original rotor is also required.
By using either mechanical centrifugal advance or a vacuum-actuated mechanism, we can change the engine timing adjustment and advance the timing as the engine runs to suit the requirements according to rpm or load. The reason for the variation in timing requirements is because although the engine runs at different speeds and under different loads, the air/fuel mixture burns at only one speed. The spark merely ignites the mixture and it will only burn at that one rate regardless of how fast the engine is turning. Thus if the piston is going to return sooner, as happens at higher rpm, the air/fuel mixture must be fired off sooner in order to allow optimum combustion time for the rapidly returning piston. Hence, as engine speed increases, the engine timing must automatically advance to occur sooner in the cycle. In other words, the faster the engine is spinning, the earlier we have to fire the plug to produce optimum power. Once computer controls were able to directly control the engine's timing, vacuum and centrifugal advance mechanisms were no longer necessary and were eliminated.
If you'd like to enjoy the advantages of an oversized distributor cap but you don't want to replace the whole distributor you don't have to. You can have the larger diameter using production Ford equipment pirated from later-model Mustangs and other Fords of the late '70s.
Another major player in the...
Another major player in the aftermarket ignition game is MSD. This MSD Pro Billet distributor is precision-built from a single piece of billet aluminum and is a great replacement for a stock distributor. Like the other choices, it eliminates the breaker points from the system, replacing them with electronic accuracy that can never come out of adjustment. This distributor must be used in conjunction with a separate ignition box, but MSD offers ready to run models as well.
Ignition Upgrades:Capacitive Discharge
A stock ignition system uses an inductive discharge. In this arrangement the coil must store and then step up the voltage between each firing. At normal rpm ranges this system works fine. However, as engine rpms climb the process begins to happen too quickly for the coil to have time to store up a complete charge between each event. The result is that the firing occurs faster than the coil's ability to store up a complete charge, meaning that the spark is fired at less than peak efficiency. The use of an MSD capacitive discharge ignition box, such as the 6AL, will eliminate this problem. The 6AL unit also incorporates a built-in rev limiter that can be set to the desired rpm with a simple adjustment.
This photo shows a close-up...
This photo shows a close-up view of a new distributor equipped with an iron drive gear. If your car has the original cam, with this gear you're good to go. The dark gray color and coarse texture on the un-machined surfaces tell you that the gear is iron.
Distributor Gear Gotchas!
One thing to be aware of when changing distributors in your engine is the material that the distributor drive gear is made out of. It must be made of a material compatible with your camshaft. If your car has the original flat tappet cam, be sure that your new replacement distributor is also equipped with an iron drive gear. If your car has a more modern roller cam, then the camshaft will be made of steel. In this case the new distributor must have a steel or bronze distributor drive gear. Any mismatch between the material the cam is made from and the distributor drive gear will result in premature wear for both gears. Besides destruction of these gears, metal shavings will end up in the engine oil and permanent damage to the engine could result.

If you've got a roller cam...

If you've got a roller cam they are usually made out of billet steel, with the gear on the cam machined out of the same material. In this case you need a steel or bronze drive gear as shown here. Different manufacturers have different requirements and recommendations so it's important to check with your cam or distributor manufacturer or both before you proceed to fire up. Any foul up involving incorrect gears in place for the distributor drive can have dire consequences.

This MSD 6AL capacitive-discharge...

This MSD 6AL capacitive-discharge ignition works differently than the inductive-style. Inside the box is a capacitor that becomes charged with 460 to 480 volts and then stores this current. When the ignition is triggered the required electricity is always at hand and the possibility of a weak spark at higher rpm is eliminated. The result is that top end power is enhanced because every combustion cycle receives a full jolt, regardless of engine rpm.

This diagram shows how simple...

This diagram shows how simple it is to equip your classic Ford car with a capacitive-discharge system. Using the Pro Billet distributor, the installation is a plug-and-play affair. Just mount the ignition box away from heat and moisture, complete the connections and you're ready to go. The illustration is courtesy of MSD Ignition.