Power Games: Engine Tuning Explained (Part Two)

Having examined how an engine works in basic terms in Part One of this post, we can now think about how to make one work better. The first part of this deals with maximizing the efficiency of the engine’s various parts. The second part looks at refining the combustion process to make the most of the exploding fuel/air mixture at every stage.

There are those who maintain that an engine is a pump, essentially an air pump. Getting the mixture into it, through it and out of it as smoothly and rapidly as possible is what spells efficiency. This is fair comment and the theory begins with the engine’s moving parts.

To become more technical for a moment, the engine’s moving parts are either reciprocating or rotating masses. Now for an analogy, from your imagination. Imagine you’re juggling with, say, tennis balls. Assuming you can juggle, you’re probably doing pretty well. Now, substitute a four-pounder cannon ball for one of your tennis balls. How’s your juggling now? Probably not too smooth. This applies to mismatched engine parts and is the reason why engine tuners will weigh a set of pistons and grind away at the heavier ones to make them all weigh exactly the same.

This principle doesn’t stop there. Connecting rods can also be ground to weigh exactly the same and a tuner will even weigh each end so he can make sure all the values match. It’s also possible to take some material away from reciprocating masses. Why do this? If these masses are lighter, less inertia is created when they accelerate and especially when they change direction. This is especially relevant when a piston changes from an upstroke to a downstroke.

Rotating masses benefit from similar attention. A crankshaft, for example, is a weighty casting. It is possible in some cases to remove excess material, again to reduce inertia. It’s also important for rotating elements to be in balance. Like our mismatched juggling balls, a crankshaft with heavy spots won’t rotate smoothly at high speed. The same goes for the flywheel. This can be both balanced and lightened; doing this will make the engine more responsive and smoother.

Mismatches can afflict the combustion chambers in the cylinder head. Say the chambers have different volumes. This will naturally mean that the compression ratio, the amount by which the fuel/air mixture is squashed ahead of the rising piston, will differ between chambers, as will the amount of power released as the fuel mixture ignites. A tuner will put valves into the chambers to seal them and allow them to be filled with a liquid. Measuring the relative amounts of liquid will reveal which chambers need material ground away to balance the volumes of all.

This kind of work comes under the general heading of ‘blueprinting’. The aim of this is to make the engine’s tolerances much closer than its manufacturer permitted. Each engine maker has ‘production tolerances’, amounts by which engine parts can vary. In blueprinting, the tuner is spending time and effort that the manufacturer would have spent on the engine, had he wanted a perfect outcome.

Tuning can go much further than blueprinting. Items within or added to the engine are modified, adapted or replaced with better ones, to improve the efficiency of the whole. Take the camshaft, for example. A standard camshaft can be replaced with one that opens the valves sooner, lets them close later and opens them more. In addition to this, it is possible to add a special kind of drive sprocket to the chain that drives the camshaft. This allows tiny adjustments to be made so the camshaft’s ‘timing’ – how it turns in relation to the crankshaft – can set very accurately indeed. And in tuning, accuracy is paramount.

Further mismatches can affect the flow of gases in and out of the engine. For example, where the inlet manifold attaches to the cylinder head, it’s possible for one or more of the apertures (ports) through which the fuel/air mixture passes to be misaligned. Careful profiling and grinding will get rid of the resultant ‘step’ that disturbs the flow; the same applies to the exhaust manifold.

Porting and polishing lie in this general area. The inlet ports, where the fuel/air mixture travels through the cylinder head, can be shaped to enhance mixture flow. It may be that they can be ‘opened up’ to make them less restrictive and the exhaust ports can be similarly improved. Many believe that the inside of the ports should be mirror-finished. This isn’t necessarily a good thing; in the inlet ports especially, some roughness of finish helps in breaking up fuel droplets in the mixture.

Big valves are another desirable addition, if they can be accommodated physically. They improve mixture flow into the engine and let exhaust gases out more quickly. Another mistake concerns believing that bigger carburettors mean more fuel goes into the engine. The amount of fuel entering the engine should be fixed in a specific ratio to the amount of air admitted. Bigger carburettors, especially ones with multiple ‘chokes’ (apertures or barrels) simply let more air in. Like a free flow air filter and a big bore exhaust with an unrestrictive silencer, all these modifications let the engine handle as much airflow as possible.

You may have noticed a paradox here. In the not-too-distant past, an engine with two overhead cams, more than two valves per cylinder, a very high compression ratio and impeccable component tolerances and balance was considered highly tuned. Nowadays, such characteristics aren’t considered unusual. But what allows modern engines to be so efficient? The handling of fuelling and, in some instances oil distribution, using microprocessor control. This is, as they say, another story…watch this space for information on engine management.


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