Theory And Practice Of Cylinder Head Modification PdfBy Lea C. In and pdf 13.04.2021 at 07:47 5 min read
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Cylinder Head Design and Modification - Getting Started From Engine Builder Magazine, by Ken Weber No one can teach you how to port heads in a single magazine article, because every job is unique to itself and its intended use.
- Two-stroke engine
- Internal combustion engine
- Diesel engine
- The theory and practice of cylinder head modification.
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Cylinder Head Design and Modification - Getting Started From Engine Builder Magazine, by Ken Weber No one can teach you how to port heads in a single magazine article, because every job is unique to itself and its intended use. If you are serious about learning to do this combination of artwork and science called porting, I suggest you look into something like Joe Mondello's porting school.
They will teach you what tools are needed and how to use them, where to take metal out, and sometimes where to put metal in. Using porting tools properly is essential to the quality of the finished part. A grinder is not as easy to use as it looks. With a can of spray paint, or a paint gun, if you keep your finger on the nozzle or trigger at the end of a stroke, you will have runs in your paint.
And so it is with a grinder - except instead of runs, you have divots where the cutter takes too much material. If you've never done this, you should first of all, invest in the proper tools, and then practice on a junk part for a while.
Although I've done it, I don't recommend you use an electric drill. Get a proper die grinder. I prefer a foot controlled, variable speed shaft grinder with interchangeable hand pieces such as one made by Fordham Tool Co. Air powered grinders turn too many rpm. Joe Mondello is also a source for porting supplies, and he has a catalogue that will get you started.
They have a catalogue and also sell the Fordham grinders. SAE sells books and engineering papers on the subject, and Motorbooks motorbooks. You should start building a library, and get friendly with it. If you have one, get out your high school physics book and study up on Bernoulli's equation.
It describes the relationship between pressure and velocity in a fluid as it flows through a pipe, which changes in cross sectional area along its length.
Bernoulli's equation translated, says that as you increase the velocity of the fluid, the pressure of the fluid at that point decreases, and if you slow the fluid down, the pressure of the fluid increases, and how much it increases or decreases. How do you change the speed of the air in a port? Simply by making the port bigger slower or smaller faster.
Also, any fluid, including air, does not like to change direction, and doing so causes it to lose velocity and energy which is hard to recover. To better understand your mission in porting heads, you should spend some time thinking about how all this works in an engine.
Cylinder Head Design The cylinder head is the part of an engine that is most responsible for its performance characteristics. Once the basic geometry of an engine is established, there is no other part that has as much influence on the amount of power developed, and the shape of the power curve. All the other parts are merely supporting cast. So, what determines the worth of one head over another? First, you must understand that any design is a compromise between what is desirable and what is possible.
Engineers that initially design an engine rarely have free rein to make it the most powerful piece possible - and they may not want to either. Even in Formula 1, where engines are designed from scratch to make as much power as possible, there are compromises that are determined by the rules of the sanctioning body and the necessity to install the engine in the car.
Like other vehicles, aerodynamics and handling requirements require compromises in size, shape and weight of the engine. The vast majority of the aftermarket cylinder heads popular today are compromised because they adhere to the standard OEM port geometry.
This is done so the supporting components designed to that geometry can be used on the new head. As engine builders, most of us have to work with parts that already exist. They may be production parts or aftermarket parts, but they all have compromises, and it's up to us as porters, to minimize the compromise. How Airflow Is Measured. Most people interested in performance know that a flow bench is used to measure airflow, but lacking hands on experience, don't understand how it works, how it is used to measure flow in a cylinder head, or what the flow numbers actually mean.
You should know that a fluid flows from high pressure to low pressure. Air, being a fluid, follows that rule. If you turn on your vacuum cleaner, the motor creates a low pressure inside the cleaner, and atmospheric pressure, now being higher, pushes air in to fill the void. The rate of flow of the fluid is proportional to the difference in pressure. Seal the vacuum hose to the combustion chamber of a cylinder head, open the intake valve and turn the motor on.
Air will flow through the port and into the cleaner. Add a valve in the hose to regulate how much pressure or suction you are using, and a means of measuring the suction and the amount of flow - usually done with manometers - and you have a flow bench.
All this flow bench does is move air through a port by creating a predetermined pressure differential, and then measure the quantity of air being moved. Tests can be done at any pressure you choose, up to the limit of the bench's capability. Most are done at 10", 25", or 28" of water, but the trend is to higher pressures, like 60 inches.
A cylinder head adapter is commonly used to mount the head to the bench as opposed to the vacuum hose previously mentioned so the effect of cylinder wall shrouding can be simulated. Either a radiused inlet guide or an intake manifold can be attached to the head to eliminate turbulence at the manifold flange, and if testing the exhaust side, a short length of appropriately sized exhaust tubing is mounted on the header flange. A rigid fixture that will open the valve in. Mount the head on the head adapter, open the intake valve to the first increment of lift, say,.
Turn on the motor, and set the control valve at a test pressure such as 25", and record the amount of flow. Open the valve to the next increment of lift, such as.
A similar test is done at each increment of lift you wish to test. You have now flow tested one intake port, and have some data telling you how much flow your port has at 25" of water, at each increment of lift you tested. To be meaningful, all tests should be done at the same pressure, and use the same inlet or outlet configuration, and the same test procedure. Simply using a different inlet radius, valve shape, or cylinder diameter can change the flow.
In other words, sweat the small stuff and pay attention to the details to insure repeatability and make comparisons from one test to another valid. To this, you can add tests for tumble and swirl in the cylinder, do localized testing within the port with test probes to determine velocity distribution and turbulent areas, try different valve and seat shapes, and even do wet flow testing if you have the capability.
You can also reverse the head on the flow bench and check the flow characteristics around the valves in the combustion chamber blow through the intake port and suck through the exhaust port.
A standard for maximum flow through a valve is CFM per square inch of valve opening. This is used to rate the efficiency of a port.
I use the valve curtain area - the circumference of the valve head 3. This gives a percentage of the standard at each valve lift. Another way to rate flow is to relate it to the area of the head of the valve.
So now you have a means to test a port and a means to rate that port at each valve lift, relative to a standard. From that you can evaluate the efficiency of different heads based on valve size and lift.
Remember, a flow bench, like a dynamometer, is just a tool. It will give you data, but it will not tell you how to interpret that data, nor tell you what decisions you need to make regarding the suitability of the port you tested, nor will it tell you how to change the port to make it better. From this point, you must evaluate your data and make those decisions - and therein lies a large portion of the skill in modifying cylinder heads. How Airflow Influences Engine Performance Volumetric efficiency is the measure of how well the cylinder is being filled with air, as a percentage of what it would be if it were filled to the same pressure as the atmosphere outside the engine.
As the piston moves away from TDC, it creates a vacuum in the cylinder, which draws in the fresh charge of air and fuel. As the piston accelerates from TDC toward its point of maximum velocity at around 75 degrees after TDC, flow lags behind demand, creating a higher and higher vacuum in the cylinder.
Then the piston slows down until at BDC it parks for a moment before starting back up the cylinder. As the piston nears BDC, the inertia of the air from its velocity causes flow to catch up with piston demand and then finally exceed it. This packing of the cylinder continues as the piston continues back up the cylinder until the valve closes. In a properly "tuned" intake system, a pressure wave will also arrive at the valve shortly before it closes, packing even more air in the cylinder.
If it were not for the inertia of the incoming air, and resonant tuning of the. For a 4" bore by 3. It is unlikely that we will find a head for a small block Chevy that will flow this much, and if we did size the port for the CFM demand at this point in the cycle, it would be too big during the remainder of the cycle and have insufficient velocity to continue filling the cylinder after bottom dead center.
Ports and valves that are too big don't generate sufficient velocity in this segment of the intake cycle, and therefore don't make as much power as a port that is properly sized. Bigger is not always better. On the exhaust side, velocity is important too. The velocity of the exhaust pulse in the port and header creates a vacuum behind it, creating a pressure drop in the cylinder as the piston approaches TDC on the exhaust stroke.
This pressure drop from the exhaust during valve overlap, gets the intake system started before the piston even starts down on the intake stroke.
The Kinetic energy in the air moving in and out of the engine is a function of the square of the velocity, so small changes in velocity make large changes in the energy of the flow. Even though the conditions in a running engine are constantly changing throughout each intake and exhaust cycle, steady flow on a flow bench can give a good representation of the power available from the engine by approximating the average conditions in the engine.
Tests done at 25" of water test pressure seem to closely approximate the average conditions that exist in an engine. As I mentioned earlier, there is a trend to testing at much higher pressures. It may be very efficient at that velocity, but have high levels of turbulence at twice that velocity. The only way to determine the worth of a port at the higher velocities is to test it at those velocities, requiring higher test pressures. When you increase the efficiency of a port in the normal direction, you also increase the efficiency of the port in the wrong direction.
This makes the engine more sensitive to camshaft changes, and to intake and exhaust system tuning. An intake manifold or exhaust system that worked just fine before, may not work very well after the heads are done, not because it's a bad piece, but because it's the wrong piece. So, what is the process to determine the correct cylinder head or head modifications needed? Whether you are dealing with a street rod or a serious race effort, the first thing to do is determine how the engine will be used, the rpm range it will see, the engine specs, and a power goal.
I regularly deal with customers that have never answered those questions, they just want their heads ported because they believe it will make more power, but until they are answered, you have no way to determine the optimum port and valve sizes, and flow requirements.
If you want a pair of heads for a rock crawler that mostly runs just above idle, but you ported them the same as you would for a rpm bracket racer, you would probably not be happy with the results. Once these things are known, you can proceed.
Internal combustion engine
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Diesel engine , any internal-combustion engine in which air is compressed to a sufficiently high temperature to ignite diesel fuel injected into the cylinder , where combustion and expansion actuate a piston. It converts the chemical energy stored in the fuel into mechanical energy , which can be used to power freight trucks, large tractors, locomotives, and marine vessels. A limited number of automobiles also are diesel-powered, as are some electric-power generator sets. The diesel engine is an intermittent-combustion piston-cylinder device. It operates on either a two-stroke or four-stroke cycle see figure ; however, unlike the spark-ignition gasoline engine , the diesel engine induces only air into the combustion chamber on its intake stroke.
The lever on the intake manifold that actuates the tumble flaps is made of plastic. When the crankcase vent valve is defective and allows engine oil to get into the intake manifold. M — M Comparison lb-ft to rpm lb-ft rpm hp rpm hp rpm ME 9.
A two-stroke or two-cycle engine is a type of internal combustion engine that completes a power cycle with two strokes up and down movements of the piston during only one crankshaft revolution. This is in contrast to a " four-stroke engine ", which requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust or scavenging functions occurring at the same time. Two-stroke engines often have a high power-to-weight ratio , power being available in a narrow range of rotational speeds called the " power band ". Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts.
An internal combustion engine ICE is a heat engine in which the combustion of a fuel occurs with an oxidizer usually air in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high- temperature and high- pressure gases produced by combustion applies direct force to some component of the engine.
The theory and practice of cylinder head modification.
Cylinder Head Design and Modification - Getting Started From Engine Builder Magazine, by Ken Weber No one can teach you how to port heads in a single magazine article, because every job is unique to itself and its intended use. If you are serious about learning to do this combination of artwork and science called porting, I suggest you look into something like Joe Mondello's porting school. They will teach you what tools are needed and how to use them, where to take metal out, and sometimes where to put metal in. Using porting tools properly is essential to the quality of the finished part. A grinder is not as easy to use as it looks.
In internal combustion engines , variable valve timing VVT is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations are causing [ citation needed ] many automotive manufacturers to use VVT systems.
This guidebook takes do-it-yourself enthusiasts through practical methods for increasing the performance of British automobile engines by modifying cylinder heads. Completely illustrated, the instructions explain common practices and are written for both amateurs and shop pros. If you know the book but cannot find it on AbeBooks, we can automatically search for it on your behalf as new inventory is added. If it is added to AbeBooks by one of our member booksellers, we will notify you! Vizard, David. Publisher: Motor Racing Publications Ltd , This specific ISBN edition is currently not available.
Из Испании опять пришли плохие новости - не от Дэвида Беккера, а от других, которых он послал в Севилью. В трех тысячах миль от Вашингтона мини-автобус мобильного наблюдения мчался по пустым улицам Севильи. Он был позаимствован АНБ на военной базе Рота в обстановке чрезвычайной секретности. Двое сидевших в нем людей были напряжены до предела: они не в первый раз получали чрезвычайный приказ из Форт-Мида, но обычно эти приказы не приходили с самого верха.
Мысли его то и дело возвращались к Сьюзан: он надеялся, что она уже прослушала его голос на автоответчике. Чуть впереди, у остановки, притормозил городской автобус. Беккер поднял. Дверцы автобуса открылись, но из него никто не вышел.