Power Games: Engine Tuning Explained (Part One)

Modern technology means there is a variety of ways in which a car engine can be induced to yield maximum power. Many of the techniques require the use of modern equipment and the application of highly technical knowledge. However, understanding at a basic level what can be done to improve an engine’s output will help you understand not only the principles and techniques are involved but also why they are applied.

For the sake of simplicity, let’s begin with an older kind of engine. This needn’t be any particular engine but thinking about a typical, four-cylinder, overhead valve car engine fed by a carburettor will teach us a lot. It may be ‘old school’ but its operation is the same as that of any four-stroke engine.

So, we have four aluminium alloy pistons, joined by cast-iron connecting rods to a cast-iron crankshaft. The pistons run in smooth cylinder bores within the cast-iron engine block. Atop the block is a cast-iron cylinder head, which has four combustion chambers, each with two valves. A chain running from the crankshaft drives a camshaft that rotates within the cylinder head, above the combustion chambers. The crankshaft also drives an oil pump that circulates oil up from the engine’s sump though internal galleries within the engine. The various running surfaces are lubricated by the engine oil, which also runs down the cylinder bores’ walls on its way back to the sump. An oil filter is plumbed into the lubrication system.

The crankshaft also drives a pump that circulates coolant through more internal galleries within the engine block and cylinder head. The coolant also passes through a radiator, which allow excess heat to be radiated to the surrounding air. The crankshaft has one more item to drive, the distributor. This ensures a spark occurs at each sparking plug in turn, at the right time to ignite the fuel/air mixture in the cylinder concerned.

OK, let’s go on to look at a single combustion cycle, to see what the engine does. Then, we can see how we can make the engine do this better. The cycle begins with the induction stroke. The piston is drawn down the cylinder, creating a vacuum in the combustion chamber. The camshaft turns and pushes down on the stem of the inlet valve. The vacuum now draws a mixture of atomized fuel into the cylinder, via the inlet valve.

As the piston is pushed back up the cylinder by the crankshaft, the inlet valve closes. The rising piston compresses the fuel/air mixture. Just before the piston reaches the top of its compression stroke, the sparking plug ignites the mixture. The result is a powerful explosion, which blasts the piston back downwards. This is the ignition stroke; some call it the power stroke. Both valves are closed and all the force of the explosion is transmitted to the crankshaft, turning it and therefore turning the flywheel attached to the end of it.

It’s now time for the piston to be pushed back up the cylinder again. At this point, the camshaft opens the exhaust valve. As the piston rises on its exhaust stroke, the pressure it creates in the cylinder forces the spent fuel/air mixture through the exhaust valve and out of the engine. The piston is now about to embark on its next induction stroke, the beginning of its next cycle.

This describes just one cylinder’s combustion cycle. In a four-cylinder engine, there are obviously three more cylinders at work. The point is that each additional cycle is a repeat of its counterpart and all the cycles work in harmony.

It’s important to understand this, the basic principle of a four-stroke, internal combustion engine. If you do understand it, you’ll find part two of this opus, which explains how and why power-enhancing modifications are made, easier to follow.


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