How to Produce More Engine Power

How to Produce More Engine Power

Car manufacturers are constantly playing with all of the following variables to make an engine more powerful and/or more fuel efficient.

1. Increase displacement: 

            More displacement means more power because you can burn more gas during each revolution of the engine. You can increase displacement by making the cylinders bigger or by adding more cylinders. Twelve cylinders seems to be the practical limit.

2. Increase the compression ratio: 

            Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (before the spark plug ignites it). Higher-octane gasoline prevent this sort of early combustion. That is why high-performance cars generally need high-octane gasoline -- their engines are using higher compression ratios to get more power.

3.Stuff more into each cylinder: 

            If you can cram more air (and therefore fuel) into a cylinder of a given size, you can get more power from the cylinder (in the same way that you would by increasing the size of the cylinder). Turbochargers and superchargers pressurize the incoming air to effectively cram more air into a cylinder. See How Turbochargers Work for details.

4. Cool the incoming air: 

            Compressing air raises its temperature. However, you would like to have the coolest air possible in the cylinder because the hotter the air is, the less it will expand when combustion takes place. Therefore, many turbocharged and supercharged cars have an intercooler. An intercooler is a special radiator through which the compressed air passes to cool it off before it enters the cylinder. See How Car Cooling Systems Work for details.

5. Let air come in more easily: 

            As a piston moves down in the intake stroke, air resistance can rob power from the engine. Air resistance can be lessened dramatically by putting two intake valves in each cylinder. Some newer cars are also using polished intake manifolds to eliminate air resistance there. Bigger air filters can also improve air flow.

6. Let exhaust exit more easily: 

            If air resistance makes it hard for exhaust to exit a cylinder, it robs the engine of power. Air resistance can be lessened by adding a second exhaust valve to each cylinder (a car with two intake and two exhaust valves has four valves per cylinder, which improves performance -- when you hear a car ad tell you the car has four cylinders and 16 valves, what the ad is saying is that the engine has four valves per cylinder). If the exhaust pipe is too small or the muffler has a lot of air resistance, this can cause back-pressure, which has the same effect. High-performance exhaust systems use headers, big tail pipes and free-flowing mufflers to eliminate back-pressure in the exhaust system. When you hear that a car has "dual exhaust," the goal is to improve the flow of exhaust by having two exhaust pipes instead of one.

7. Make everything lighter: 

            Lightweight parts help the engine perform better. Each time a piston changes direction, it uses up energy to stop the travel in one direction and start it in another. The lighter the piston, the less energy it takes. 

8. Inject the fuel: 

            Fuel injection allows very precise metering of fuel to each cylinder. This improves performance and fuel economy.

The efficiency of the engine 

The efficiency of the engine depends to a large extent upon the following criteria:

	· Compression
	· Combustion Process
	· Air/Fuel Mixture
	· Mechanical Design
	· Lubrication

                                     

1)  Compression:

The higher the Compression Ratio or the pre-compression pressure, then the higher is the thermal efficiency of the internal combustion engine. This results in a better fuel usage and more power is developed while less fuel is consumed. The maximum compression is however limited by the Octane Rating of the Gasoline that will be used. The higher the Octane Rating the higher the compression can be.

Unfortunately, higher Octane Gasoline costs more to produce than low Octane Gasoline. Therefore the increase in fuel efficiency can be offset by an increase in fuel costs.

The Compression Ratio is based on the mechanical design of the engine and is expressed as:

 

Where:

CR = Compression Ratio

Vs = Cylinder swept Volume

Vtdc = Combustion space Volume of Cylinder

            Even more important than the Compression Ratio is the actual pre-compression pressure also called Final Compression Pressure. Although its value can be also described and figured out mathematically, it is always substantially less than the mathematical result. The actual Final Compression Pressure can be reliably obtained only by a measurement with a special tool, the Compression Tester.

            It is however important to know what the Final Compression Pressure should be for the particular engine. This specification can be usually found in a "Shop Manual" for the particular engine. The difference between the measured and specified values for the Final Compression Pressure determines the "Sealing Quality" of the combustion chamber.

            The quality of the combustion chamber sealing by means of the Piston Rings and the Valves is a measure of the condition of the engine. Lubricant can also affect the quality of the sealing between the Rings and the Cylinder bore.

            When the Final Compression Pressure is too high on a used engine, it usually means that the combustion chamber and the piston crown have excessive amounts of carbon deposits that have been formed due to any of the following:

 

1.     Incomplete combustion

2.     Use of poor quality fuel

3.     Use of poor quality lubricant

If the Final Compression Pressure is too low on a used engine, it usually means that the engine has any of the following problems:

	Has excessive amount of cylinder wear (due to poor lubrication)
	Has sticking piston rings (poor lubricant)
	Has burned exhaust valves (poor fuel or incorrect ignition timing)
	Has damaged cylinder head gasket
	Has sticking intake or exhaust valves (poor lubricant)

 

2) Combustion Process:

            For the quality of the combustion process it is of prime importance that the fuel mixes intimately with the air, so that it can be burnt as completely as possible. It is important that the flame front progresses spatially and in regular form during the power stroke, until the whole mixture has been burnt. The combustion process is considerably influenced by the point in the combustion chamber at which the mixture is ignited, and by the mixture ratio as well as the manner in which it is fed into the combustion chamber.

            Combustion is optimal and the efficiency of the engine is at its best when the residual gases contain no unburned fuel and as little of Oxygen as possible. The Hydrocarbons are broken up during the combustion into their constituent parts, they are Hydrogen and Carbon. On complete combustion, the Carbon and Hydrogen burn to form Carbon Dioxide and Water vapor. When the combustion is incomplete the exhaust gases also contain other undesirable constituents.

3)  Air/Fuel Mixture:

            The Specific Fuel Consumption of an engine is defined as the amount of energy produced per given amount of fuel consumed in the combustion process. The amount of fuel is quoted in grams or kilograms and the amount of energy produced in Kilo-Watt-Hours or Horsepower per hour.

            Internal combustion engines can consume as little as 300 grams per kWh or as much as 1,200 grams per kWh.

            In general, the Specific Fuel Consumption is at its greatest (least efficient) when the engine is subjected to low loads, such as idle. This is because the ratio between the idling losses (due to friction, leaks, and poor fuel distribution) and the brake horsepower is the most unfavorable.

            Most engines have the lowest Specific Fuel Consumption at a three-quarter load, which is at 75% of the maximum power output and at about 2,000 RPM.

            The Specific Fuel Consumption of the engine is for the most part dependent on the mixture ratio of the Air/Fuel mixture. Consumption is at its lowest with an Air/Fuel Ratio of approximately 15 pounds of Air to one pound of Fuel. This means that 10,000 gallons of Air is needed to burn one gallon of Gasoline.

4) Mechanical Design:

            The mechanical design of the internal combustion engine has not changed since its conception in 1876, mainly because it works. The problem is, that it has been invented long before there was a thorough understanding of thermodynamics or of the chemical reactions during the combustion process. Further cheap and plentiful fuel -- Gasoline was easily available and until a few years ago there was no concern with conservation or pollution.

            As a result, the internal combustion engine is an energy efficiency dinosaur that refuses to die.

            To give you some idea why that is so, let’s consider this:

            Gasoline contains about 42 to 43.5 Mega-Joules of energy in one Kilogram that is equal to about 18,060 to 18,705 Btu per pound.

            The pie chart on the next page will show you where all that energy that is available in Gasoline goes: