Engine Tuning Essentials

June 23rd, 2009

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After your auto left the factory the engine was set up perfectly for most of drivers who need little more than efficiency, reliability and economy. Still, there are those of us who see the vehicle as a platform for creating something a bit more unique by tuning its engine. This can be as simple or as complex as your wallet can take, but there are some conventions that ought to be followed primarily. Before starting any type of engine tuning, you should make sure that your engine is running as the producer planned. After this has been done you are set to extract some more power from the engine.

Step one is to obtain cleaner (and rather cooler) air in the engine and let more fumes to exit the engine. This is done by adding a performance air filter and a performance exhaust. The air filter, can be either a replacement panel that fits in the presented airbox or a complete replacement kit comprising of a cone filter and tubing. There are also quite a few options for the exhaust system. Most autos have three sections in the exhaust system, the manifold starting at the engine block, a centre segment and the muffler at the ending. Replacement of the centre and miffer is the least you must do.

Replacing the exhaust and filter will not give that much power, but will enable the engine breathe more generously and you will feel some more reaction from the vehicle under speeding up. At this stage we reach a fork in the path of tuning. The road which you choose to follow depends on what type of engine you own. The first way is for naturally aspirated engines (with no a turbo) and the second path for forced induction cars (turbo or supercharged). At this phase it would also be advisable to check the braking, suspension system, tyres and the gearbox as with extra power available, stopping and handling are more important than before.

For a naturally aspirated engine, the next step is to work on the head by porting it to rise the displacement and gain a significant amount of power. The camshaft can also be swaped for a fast road type. You must then look at the ancillaries such as spark plugs, the fuel pump, the oil pump, before going on to the bottom end and the crank. For a forced induction vehicle you want to look at the ECU and change the intercooler with a superior size model. The ECU should be checked and either re-programmed or changed with a performance item to increase power and increase drivability. Depending on your taste you might wish to add a blow-off valve to let the turbo to work more effectively. Water injection, stronger pistons and an bigger turbo should be next on your list. You can as well take into account adding a turbo to a naturally aspirated engine to significantly increase the power for a relatively small sum of cash.

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Engine Compression Ratio – Static vs Dynamic

June 22nd, 2009

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If we split this expression apart and look in the dictionary we will get:

Compression – as an adjective means to squeeze.
Ratio – as a noun means a proportion of two things.

When talking about engines we can distinguish two kinds of compression ratios (CR): static and dynamic.

Static CR

The static compression ratio is defined as the volume of the combustion chamber once the piston is in the bottom dead center (BDC) – very bottom of it’s journey – divided by the volume of the combustion chamber in it’s top dead center (TDC) – very top of it’s travel.

Static compression ratio is one factor that influences how completely the air-fuel mix is burned, once it has been lit by the spark. If you burn all of the air-fuel mixture you make more hp. If there is some leftover unburnt air-fuel mixture following the spark has been lit, you have not gotten all the power you can get out of the mixture. This completeness of burn is called thermodynamic efficiency.

Improving thermodynamic efficiency is one of the 3 key power-gaining techniques existing for engine builders. But, the problem is that as you rise CR, you rise cylinder pressure and temperature inside the combustion chamber. Once air is squeezed hard inside a closed container as a cylinder, the pressure inside goes up the harder you squeeze. As pressure rises, so does temperature. This can cause a process called self-detonation – the air-fuel mixture ignites on it’s own lacking the spark.

Secondly, as you increase static CR more and more, the cylinder pressures grow progressively. The piston must work much harder to compress identical amount of air-fuel mixture delivered into the chamber due to this higher pressure. This negative work slows the piston speed momentum which affects the power you generate.

So you are able to create extra power by improving burn efficiency via increasing the static CR up to a point. For street engines, the highest static CR on pump gas is near 12.5:1 CR if you know how to tune. If you don’t, the maximum is round 11.5:1 CR. For a race engine, the spot at which cranking pressure causes negative work and affects power output is approximately 14:1 CR.

Dynamic CR

The piston is constantly travelling up and down however the intake valve opens and closes in this time also.
At the same time as the piston is starting to squeeze at BDC, the intake valve is starting to close. The intake valve is not entirely shut until the piston is reaching TDC. There is a connection between the cylinder combustion chamber and the intake port/intake manifold runner, when the intake valve is still in part open. As the piston is squeezing and coming up to TDC, some cylinder pressure can bleed up into the intake port which decreases overall cylinder pressure.

If you use your adjustable intake cam gear to close the intake valve earlier, the amount of cylinder pressure bleeding up the intake port is decreased. The cylinder pressure builds up faster and you get a better burn.

If you let the intake valve close later, additional cylinder pressure will bleed out or be lowered and the burn will be less complete.

This is why it is key to increase your static CR when you get extremely longer duration cams.

You desire a fast, complete burn of the air-fuel mixture to make power.

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Engine Tuning – Power versus Torque

June 21st, 2009

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It seems that lots of people are puzzled about the relationship between power and torque.

“Which do I need more – power or torque – to go quick?” – It is a popular area of debate with car enthusiasts – but one that seems to be never-ending and regularly unsolved. In order to be able to properly deal with the matter, it is necessary to have an knowledge of what the terms in fact mean.

Torque

Torque is simply a amount of the twisting force that is applied in an attempt to rotate an object. It is a force that is applied to a lever arm, and is measured in Newton Metres (Nm). Newtons are a unit of force, and at the surface of our planet a 1kg object will apply a force on the ground of 9.8N, because of gravitation. Torque is, in effect, the outcome of the force and the length of the lever arm. Understood this way, it is obvious that there are two ways of rising torque. You can either increase the force or rise the length of the lever arm. Looking at an engine we can say that the lever arm is the stroke and the force comes from capacity. So, to increase torque, rise the stroke, or rise the capacity, or do both.

Power

Power is defined as the rate of doing work, and has units of Kilowatts (kW named after James Watt) or horsepower (old Imperial units).

Watt wanted to be capable to rate the power output of his steam engines in order to advertise them. He decided that the most rational unit of power to weigh against them to was the rate at which a horse could do work. He tested the capability of a variety of horses to elevate coal with a rope and pulley and in the end settled on the definition of a “Horsepower” as 33,000 foot pounds per minute.  In metric, the Watt is defined as the power to do one Joule of work per second. One horsepower is equivalent to about 746 Watts.

The relationship

Now, another aspect to realize is that power and torque are intimately related. With engines, power is the torque multiplied by the radial velocity.

Power (kW) = (Torque (Nm) x RPM) /9549
Power (hp) = (Torque (lb/ft) x RPM) /5252

As you can see torque and power are (almost) flip sides of the same coin. Rising the torque of an engine at a particular RPM is no different as increasing the power output at the same RPM. Power is as useful and important in determining automobile performance as is torque.

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