Another option for automotive enthusiasts, especially those with older gasoline-fuelled vehicles is a technology upgrade. Sometimes classic cars need to be left alone but often a technological upgrade will make the car much more enjoyable. Cars of the sixties and seventies are good candidates for upgrades because the cars themselves are still easily available but more importantly, upgrade parts are also available. The upgrades that people can consider could really involve almost any component, but we will focus only on engine-related upgrades that improve performance and fuel efficiency.
Without removing the entire engine and replacing it with a modern equivalent, we will further restrict our focus to the control of the combustion of fuel in the engine. This implies controlling the fuel mixture and the timing of the ignition. In the sixties, carburetors were the norm for controlling the fuel mixture and Kettering ignition system (battery, points & condenser, coil, and distributor) were the norm for controlling the spark. As governments began legislating tighter control of emissions, engine controls became more complex. This lead to the creation of electronic ignition and fuel injection.
To some degree, any engine can be upgraded and the main reason anyone would do this is for personal satisfaction. The payback for any upgrade in terms of reduced fuel consumption would likely be many years, but this depends greatly upon the price of fuel and your current fuel economy. If you do a lot of driving and you need a way of cutting your operating costs, you should really consider buying another car. However, if you love your older car and want to give it a little more oomph because you can, read on.
Engines require the right fuel mixtures for the conditions of operation. For lightly loaded cruising conditions, lean fuel mixtures result in the lowest consumption but tend to increase NOx emissions. Maximum power requires a rich fuel mixture, which tends to increase hydrocarbon and carbon monoxide emissions. Manufacturers experimentally determined the best carburetor calibrations to accomplish these goals. However each cylinder did not receive the ideal fuel mixture for each condition because of the limitations of the intake manifolds. Even though manufacturers invested a great deal of their resources into designing intake manifolds, by the very nature of carburetors, the designs of intake manifold are a compromise of many factors. The fuel mixture delivered by carburetors is the best guess that manufacturers experimentally determined.
Once the carburetor has metered the correct amount of fuel into the intake manifold and the fuel mixture has been delivered to the combustion chamber, the ignition system must ignite it so that the peak pressures developed in the combustion chamber occur when the piston is positioned to maximize the torque produced on the crankshaft. Too soon and the energy is wasted counteracting the motion of the crankshaft. Too late and the energy is wasted to the exhaust.
The fuel mixture burns at a fixed rate so that the flame front has a fixed velocity as it travels from the spark plug to the far reaches of the combustion chamber. This implies that combustion must begin sooner as engine speed increases. Combustion must begin sooner also when fuel mixture is lean under cruising conditions. The distributor's spark advance mechanism is what controls when the spark plug fires relative to piston position. Early distributors had a simple mechanical advance system that used centrifugal weights to adjust spark timing. They further used a vacuum canister to further advance the timing with high manifold vacuum.
The Kettering ignition system had a number of limitations that were overcome by electronic ignition systems. Because the dwell angle (the number of degrees of distributor rotation that the points are closed) was controlled by a cam in the distributor, increasing engine speeds reduced the time available to fully saturate the magnetic field (flux) in the coil As RPMs increased , the quality of the spark decreased. Also, dwell was only correct with brand new points, as the cam follower and the points wore with use, the dwell would change. The faster the voltage in the coil's primary windings collapses when the points open, the higher the voltage produced in the coil's secondary windings.
Electronic ignitions have a variable dwell that tries to maintain a constant high tension voltage. As there are no components to wear, spark quality is more constant. There are two main types of electronic ignition: Transistor Controlled Ignition (TCI) and Capacitive Discharge Ignition (CDI). The difference between them is that the TCI system is very much like a points and condenser system which uses current flow through the primary windings of the coil to saturate the magnetic field in the coil. A TCI system uses transistors instead of the points and condenser to almost instantaneously interrupt the primary current. A CDI system uses a high voltage pulse to flow through the coil. The coil in this case is used to step up the voltage and functions more like a transformer than an inductive voltage storage device. One big advantage CDI has over TCI is a much higher RPM capability because of its very short primary voltage pulse.
Once combustion is complete, another requirement for power and fuel economy is for the products of combustion to be removed from the engine. The exhaust system accomplishes this but, as with the intake system, the components are a compromise of many factors. Exhaust manifolds are commonly made of cast iron and are designed to fit tightly against the engine. Exhaust flow was and sometimes still is of secondary importance. To keep production costs down, exhaust pipes are as small a diameter as possible.