Maximizing Engine Power

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Maximizing Engine Power

Postby iqurean on Thu Jul 30, 2009 3:13 pm

Custom-car.us is all about engine tuning and car performance; so if you want to know about car tuning, how to increase engine power and how to modify your car, then you've come to the right place. However, before we can start talking about engine tuning and increasing engine power and torque, we first need to have a basic understanding of how an internal combustion engine produces power. Therefore, over the next few pages of this section, we'll discuss the various basic concepts and principles of the internal combustion engines and the common terms used to discuss engine modifications, such as volumetric efficiency, engine displacement and air density as all of these influence engine power and performance. We also have a glossary of car modification terms that you can check for the meaning of some of the terms we use on this site. Once we have a clear understanding of how a four stroke engine produces power, we can move on and start make our P.L.A.N.s to increase engine performance.

The four stroke engine
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Although there are two types of internal combustion engines, namely the two stroke engine and the four stroke engine, we're only interested in car performance and since the two-stroke engine is not used on cars, we won't be discussing that engine here. Instead we'll focus out attentions soely on the four-stroke engine because custom-car.us is all about car tuning and because cars use the four-stroke engine and not the two-stoke engine. If you're looking for information about the two-stroke engine, you could try How Stuff Works or Wikipedia.

The Wankel rotary engine
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There are also numerous derivatives of the four stroke engine – diesel engines, petrol engines, four cylinder engines, straight sixes, boxer engines, rotary or wankel engines, turbocharged engines, supercharged engines, etc. With the marked exception of the rotary engine, all four stroke engines have a common basic design – they all consist of individual cylinders with pistons that are connected to a flywheel by a crankshaft, and they all make use of what is known as the Otto Cycle. This makes it fairly easy to discuss basic engine power concepts as we don't need to concern ourselves with V's and straights, boxers and horizontally opposed engines. Instead our discussion can and will be all about the four stroke internal combustion engine. In addition, the deisle engine has had a resurgence in recent years and has become more of a performance engine, especially the turbo-diesel engine. A lot of what we discuss here can be applied to modern diesel engines but there are some aspects of engine modification that are specific to diesel engines; for this reason we'll discuss diesel engines and diesel engine modifications on their own.
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Re: Maximizing Engine Power

Postby iqurean on Fri Jul 31, 2009 2:42 pm

The Four Stroke Engine

When you want to increase engine power on a four stroke engine, it is the efficiency of each stroke, particularly the intake and exhaust strokes, that you need to improve. Understanding the four stoke cycle of the internal combustion engine and how it produces power is important when you want to increase engine power. So let's begin with the four stroke cycle which is also known as the Otto cycle. If you're familiar with the four stokes of the Otto cycle feel free to head on over to power basics. Otherwise read on as this section is important to understanding engine tuning.

The intake stroke is the first stroke of the Otto cycle. During this stroke the intake valve opens as the piston moves from top dead center (TDC) to bottom dead center (BDC). The downward movement of the piston creates a vacuum in the cylinder that causes air/fuel mixture to be drawn into the cylinder. The intake valve usually opens slightly before the stroke begins and closes slightly after the stroke ends to maximize the amount of air/fuel mixture that can be drawn into the cylinder.

The volume of air/fuel mixture that is drawn into the cylinder, relative to the volume of the cylinder, is called the Volumetric Efficiency (VE) of the engine. Maximizing the VE of the engine is an effective method of engine tuning that we can use to increase engine power, especially as stock engines generally have a VE in the range of 85% while older engines have a VE in the range of 70%.

The compression stroke is the second stroke of the Otto cycle. Both the intake and exhaust valves are closed. The piston moves from BDC back up to TDC, forcing or compressing the air/fuel mixture into the combustion chamber of the cylinder head. The movement of the piston also causes turbulence which mixes the air/fuel mixture further, allowing more of the chemical energy in the fuel to be released during the power stroke.

While it is the fuel that stores the chemical energy that drives the engine, it is the air that allows the fuel to burn and release its energy. Too little air leads to a rich fuel mixture that does not burn completely and does not release all the energy in the fuel, robbing the engine of power and economy. Too much air leads to a lean fuel mixture that burns too quickly. When the air/fuel mixture burns too quickly, it spends its energy too soon and creates too much pressure too quickly. This can cause irreparable damage to the engine. The chemically ideal ratio of air to fuel is 14,7 parts air to 1 part fuel (14,7:1) and is referred to as the stoichiometric condition. However, the air/fuel mixture requirements of the internal combustion engine are influenced by RPM, engine load and temperature. Heat is required for fuel vaporization. Therefore, in cold start conditions, a richer mixture is required and at full throttle, or wide-open-throttle (WOT), a leaner mixture is required. This is why fuel injection has a major advantage over the carburetor; it can provide the correct air/fuel mixture under varying conditions.

The power stroke is the next stroke in the Otto cycle and is also the start of the second revolution of the engine. The intake and compression strokes require a complete revolution of the engine, while the power stroke and the exhaust stroke require another revolution; in other words, the four stroke cycle is completed over two revolutions of the engine.

Just before the start of the power stroke, the spark plug fires, igniting the air/fuel mixture which then burns in a controlled manner. This causes an increase in temperature and an expansion of the gasses in the combustion chamber, and ultimately increases the pressure in the combustion chamber. This pressure increases progressively and acts upon the top of the piston, pushing it down the bore to BDC. It is important to note that the pressure increases progressively until peak cylinder pressure is reached at approximately 12° to 14° after TDC. If peak pressure is reached at TDC, there would be too much pressure on the bearing and crankshaft, which would absorb a large amount of the power being produced.

The pressure pushing down on the piston and forces the crankshaft to rotate, converting the chemical energy in the fuel to mechanical energy. Unfortunately, the internal combustion engine is not very efficient and a lot of this energy is lost through heat that is absorbed by the engine, and lost through the exhaust. Though the heat energy that is lost through the exhaust can be used to drive a turbocharger so it can't be all that bad, can it?

The burnt air/fuel mixture is expelled from the engine during the exhaust stroke. The exhaust valve opens slightly before the stroke begins. With the exhaust valve open, the movement of the piston from BDC to TDC forces the burnt air/fuel mixture through the exhaust valve and out of the engine. Usually, the exhaust valve opens slightly before the stroke begins and closes slightly after the stroke ends, allowing the engine to expel as much burnt air/fuel mixture as possible. Any burnt air/fuel mixture or exhaust gasses that remain in the combustion chamber after the exhaust stroke will contaminate the fresh air/fuel mixture that in drawn into the cylinder on the next intake stroke, and will effectively reduce engine power.

The intake and exhaust valves can open slightly before the start of their respective strokes and can close slightly after the end of their respective strokes because the linear movement of the piston slows down dramatically to a dead stop as it reaches TDC and BDC. However, the opening and closing of the valves must occur at exactly the correct moment to ensure maximum engine power, particularly as the fresh air/fuel mixture coming into the cylinder just before the end of the exhaust stroke helps push out more of the burnt air/fuel from the previous cycle through a process called "scavenging". We discuss valve timing in our section on camshafts and cylinder heads; but in our next section on engine basics, we'll look at how to increase engine power.
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Re: Maximizing Engine Power

Postby iqurean on Fri Jul 31, 2009 2:45 pm

Basic Engine Power

There are four ways in which you can increase engine power:

Increase the engine displacement by boring the motor out or stroking the crankshaft.
Increase the engine speed.
Improve the Volumetric Efficiency of the engine.
Increase the air density.
Essentially, all these engine tuning methods seek to improve air flow in and out the engine.

DISPLACEMENT
Engine capacity or displacement is measured by the formula (π/4 × bore2) × stroke × cylinders. The bore is the diameter of the cylinder; thus (π/4 × bore2) gives us the area of the cylinder. The stroke is the distance the piston travels from TDC to BDC and gives us the length of the cylinder. Multiplying these two measurements gives us the volume of one cylinder. Multiplying the volume of each cylinder by the number of cylinders that engine has will give us the total displacement of the engine. Thus, by increasing the area, length, or number of cylinders, we can increase the displacement of the engine.

Unfortunately we can't increase the number of cylinders so we're left with the area and the length. We can increase the cylinder area by boring the motor. This is the easiest way of increasing displacement, but is restricted by the thickness of the cylinder walls, and the space between the cylinders. We can also increaser the length by stroking the crankshaft. This is more complicated as it requires the offset machining of the big-end journals on the crankshaft and possibly on the conrods. If the big-end journals of the conrod cannot be ground, you must either find slightly longer conrods that will fit, or pistons with a shorter compression height, i.e., the distance between the center of the gudgeon pin and the piston top. Stroking is restricted by the clearance between the rotational diameter of the crankshaft and the engine block.

ENGINE SPEED
Increasing engine speed does not increase the power per cycle, but increases the rate at which power in produced as the number of cycles per time frame increase. In other words, power is being produced more often as the Otto cycle is being completed much quicker. Increasing engine speed above the red line of the stock engine generally requires a complete engine rebuild with forged pistons, stainless steel conrods, stainless steel crankshaft, and a more robust valve train.

VOLUMETRIC EFFICIENCY
The Volumetric Efficiency (VE) of an engine is the amount of air/fuel mixture that is ingested by the engine during the intake stroke, relative to the engine’s displacement. There are a number of factors that prevent a stock engine from achieving a 100% VE. Chief among these are restrictions in the airflow path of the intake and exhaust, valve overlap effects, and reversion.

Restrictions in the airflow on the intake side include the air filter, the throttle body, the plenum and runners, and the intake port. These restrictions can be overcome to some degree by fitting a high-flow air filter, and improving air flow through porting and gas flowing, especially on the cylinder head.

Restrictions on the exhaust system include the exhaust header, the catalyst converter, and the mufflers. Unfortunately, anti-emission legislation requires that the catalyst converter be retained on street legal cars but restrictions in other areas of the exhaust system can be overcome by fitting a free flow exhaust header and free flow exhaust mufflers.

Fitting a free flow exhaust system will also reduce reversion, which is the flow of exhaust gasses back into the combustion chamber. Reversion causes contamination of the air/fuel mixture and takes up space that the air/fuel mixture should fill, thus reducing volumetric efficiency. Too much back pressure in the exhaust system will cause reversion. As Bre suggests in our exhaust guide, fitting a free flow exhaust header that is slightly larger than the exhaust port on the cylinder head reduce reversion but an anti-reversion (AR) header that is specially designed to inhibit reversion would be even better.

AIR DENSITY
Denser air produces more power because it has more air molecules per volume. There are two ways in which air density can be increased – by lowering the air temperature, or increasing air pressure. Unfortunately, we can't really lower the air temperature but we can increase air pressure. The easiest way to increase air pressure would be to drive at lower altitude but this isn't really practical. The other way is to use forced induction. The three forms of forced induction are:

Installing a supercharger.
Installing a turbocharger.
Installing Nitrous injection


Bre doesn't believe NOS is forced induction, but that's his problem. Forced induction is the easiest ways of improving engine power and if done correctly, you can easily increase power by up to 50%! Now that's major engine power!
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Re: Maximizing Engine Power

Postby root on Sun Aug 02, 2009 3:47 pm

interesting stuff!

Many of the tuning tips are however illegal here :(
Come and discuss at the most lively forums about Cars, Bikes, 4x4s...at http://www.autodealer.ae at the Autodealer UAE Forums.
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Re: Maximizing Engine Power

Postby T.N.T on Sun Aug 02, 2009 10:33 pm

Depends on how many 'brown shirts' you know ;)
Give respect, get respect.
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Re: Maximizing Engine Power

Postby root on Sun Aug 02, 2009 11:10 pm

well, rather the right brown shirt!
Come and discuss at the most lively forums about Cars, Bikes, 4x4s...at http://www.autodealer.ae at the Autodealer UAE Forums.
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Re: Maximizing Engine Power

Postby iqurean on Mon Aug 03, 2009 1:57 pm

@ ROOT
Thanks.
@T.N.T
Brown Shirts, lolz..
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Re: Maximizing Engine Power

Postby iqurean on Mon Aug 03, 2009 2:05 pm

Engine Building for Power and Reliability

If you're planning to do some serious modifications to a four stroke engine, you'd better do it right if you don't want to end up with an expensive pile of scrap metal. It's easy to slap on a turbo and run mild boost on a stock engine or even fitting a bigger turbo to an OEM turbo engine, but if you're looking for serious power, you have to rebuild the subassembly to ensure that it can handle the additional power without disintegrating. Obviously you need to ensure that your drive train can handle the extra engine power as well, but in this section we'll discuss engine building for maximum power, starting with the subassembly.

THE CYLINDER BLOCK

You've got to start by ensuring that your cylinder block is race grade. Even if you're just building a street race car, engine tuning would be senseless if the block is not up to the job. Start by pressure testing the block. If you have an air compressor you can do this yourself. Strip down the engine but leave the Welch plugs and oil gallery plugs in place. Fit the bare cylinder head to the cylinder block using new head gasket or one that's not too worn. Close all water opening off with steel plates. One of the plates must be fitted with an air line fitting that you can connect your air compressor to. Gradually increase the pressure in the block to 40 psi. Don't increase the pressure too quickly as a loose fitting Welch plug or a weak spot in the block could blow out can cause you serious injury. If everything is still in place, gradually increase the pressure to 50 psi. Now spray the block with a mild water/detergent mixture. Carefully check the block for air bubbles. If you see bubbles, either have it repaired or test another block. If you get no bubbles, release the air pressure and remove the cylinder head. Use a plug tap to clean the head stud and main bearing cap threads and chamfer any stud hole that is not already chamfered. This will prevent the thread from pulling up. Grind away any casting sag, especially around the main bearing webs, the sump pan deck, and the valley area of a Vee engine. This will prevent cracks from developing. Now remove all the Welch plugs and oil gallery plugs and have the block boiled and cleaned in a chemical bath. This will remove all rust and scale in the water channels, and the caked oil in the oil galleries.

THE CRANKSHAFT & CON RODS
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The stock crankshaft and con rods are usually cast iron items that can be retained if the engine is not required to handle high boost pressures, high horse power, and high revs. Forged crankshafts and con rods are much stronger and are more suitable for high load, high rev engines. In either event, you should have the crankshaft and con rods Magnafluxed to check for cracks.

If the crankshaft has no cracks, check it for straightness. A crankshaft that is even 0.002in out of straight will increase bearing load and will be the cause of bearing failure. If your crankshaft is out of straight, you have two options – either have the crankshaft straightened or machine the crankshaft's main journals so that crankshaft rotation is true. However, straightening a crankshaft that is to be used for a high boost, high horse power, and high rev engine is a waste of time and money as the combustion pressure and inertia loads will reverse the straightening process. Machining the crankshaft journals will also weaken the crankshaft. Ultimately, replacing a bent crankshaft is your best option.

It goes without saying that all the crankshaft journals should be checked for roundness and size. The same goes for the big end on the con rods. The crankshaft, con rods, and flywheel should then be balanced statically and dynamically to reduce shock loading and vibration.

THE PISTONS
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The next thing you need to consider is the pistons. Most OEM engines are fitted with cast aluminum pistons with a slotted oil groove. High performance OEM engines may be fitted with hypereutectic cast aluminum pistons that have a higher silicon content. The higher silicon content makes the cast material much harder and more wear resistant, which allows these pistons to withstand greater temperature and pressure loads. This makes these pistons ideal for street racers. However, the higher silicon content also makes the pistons more brittle and prone to breaking under detonation. Thus, these pistons are not a good choice for forced induction applications where the possibility of detonation in greatly increased.

Forged pistons, on the other hand, have much denser and even harder than hypereutectic cast aluminum pistons but are not as prone to breaking under detonation. Forged pistons also have drilled oil holes round the oil groove rather than a slot in the oil groove. This makes them the best option for high horse power, forced induction engines.

Pistons can also be either full skirt pistons or slipper type. The full skirt pistons are heavier but stronger and less prone to wobble. Needless to say, they would be the best option for any engine modification project.
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Re: Maximizing Engine Power

Postby iqurean on Mon Aug 03, 2009 2:09 pm

The Diesel Engine

The diesel engine was developed by Rudolf Diesel and was patented in 1892. Diesel engines are very similar to petrol or gasoline engines in that both rely on the Otto cycle to convert the chemical energy in fuel into mechanical energy and, in so doing, produce power. The major difference is the way fuel is delivered to the combustion chamber and the way the fuel mixture is ignited. Firstly, in gasoline engines, the fuel is usually fed into the intake manifold or the intake port where it is combined and mixed with the intake air, which is also called the intake charge. In modern diesel engines, the fuel is injected directly into the combustion chamber. This means that only the intake charge is compressed during the compression stroke and the diesel is only introduced once the intake charge has been compressed. Secondly, in gasoline engines, the fuel mixture is ignited by a sparkplug, while in diesel engines the fuel is ignited by the heat from the compressed air in the combustion chamber. However, diesel requires a much higher temperature than petrol before ignition (not spontaneous ignition) can take place.

These differences has important consequences for the modification of diesel engines, especially when you consider the differences between diesel fuel and gasoline.

THE DIFFERENCES BETWEEN DIESEL AND GASOLINE

For starters, diesel is a heavier fuel than gasoline. In other words, it contains more carbon atoms in longer chains than gasoline (technically, gasoline is typically C9H20, while diesel fuel is typically C14H30). Because it is heavier, diesel is much more stable that gasoline and vaporizes at a much higher temperature than gasoline. It also vaporizes much slower than gasoline and burns much slower. The result is that diesel requires a much higher temperature to ignite. Gasoline, for example can burn at temperatures of -40° F while diesel requires a temperature of at least 143° F!

The main point, however, is that diesel burns slower than petrol. This means that it will produce a steady pressure on the piston for longer. Consequently, diesel can be ignited at a higher temperature, and indeed can be allowed to reach the point at which it will ignite spontaneously. The interesting thing is that diesel needs a temperature of 410° F to ignite spontaneously but will ignite or burn at a much lower temperature of 143° F. Consequently, diesel cannot be introduced into the combustion chamber until the correct temperature is reached, or else it will pre-ignite. Now, to reach the required temperature, air in the combustion chamber must be compressed much more than in a gasoline engine, and because there is not fuel in the combustion chamber, the intake charge can be safely compressed without the danger of pre-ignition. Thus a gasoline engine will typically have the compressions ratio would of somewhere between 1:9 and 1:12 while a diesel engine will typically a compression ratio of around 1:25! And it is this higher compression ratio, as well as its higher vaporization point and slower burning rate and the fact that diesel has about 17% more energy density than gasoline, that makes diesel much more efficient than gasoline.

Now you're thinking why not use direct injection in a gasoline engine so we can increase the compress without pre-ignition? Indeed some manufacturers to employ direct injection on gasoline engines, but without the higher compression ratio because gasoline will burn too quickly at higher temperatures, hence the need to keep the temperature of the intake charge down in a gasoline engine. Remember, diesel burns at a slower rate than gasoline and therefore can be ignited at higher temperatures.

DIESEL ENGINE MODIFICATIONS

When it comes to modifying a diesel engine, you can apply the same techniques that you would apply to a gasoline engine, except for ignition system obviously as diesel engine has no spark plug. All the basics apply, i.e., increasing the engine displacement, increasing the engine speed, improving and increasing the air intake, and increasing the volumetric efficiency.

Nonetheless, there are a number of things to consider before attempting to modify a diesel engine.

Firstly, components in the diesel engine are exposed to far higher pressures and temperatures than the components in gasoline engines. Therefore, diesel engines need to be more robust with thicker cylinder walls and stronger pistons. Should you decide to increase the displacement of your diesel engine by boring out the cylinders you should ensure that you improve your cooling system.

Secondly, diesel burns at a much slower rate than gasoline; therefore a diesel engine will operate at a much lower RPM. This is natural, and getting the diesel engine to operate at higher speed will mean increasing the temperatures in the combustion chamber, which would require thicker cylinder wall and much a better cool system, and improving the cooling system is easier said than done because of diminishing returns!

Furthermore, increasing the temperatures in the combustion chamber will increase the heat in the intake manifold, and will result in a reduction of air density. Consequently, we're dealing with even more diminishing returns! Still, maximum power will be reached at relatively low RPMs because of the slow rate at which diesel burns and will drop off dramatically at higher RPMs.

Thirdly, increasing the amount of air ingested by the engine will require a proportionate increase in the amount of fuel injected into the engine. Thus bigger injectors, a higher fuel pressure will be required, or a remapped engine control unit (ECU) would be required. On some turbo-diesel engines, a remapped ECU has led to impressive improvements in power and should be the starting point in your quest to squeeze more power from a diesel engine.
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