The internal combustion engine burns fuel within the cylinders and converts the expanding force of the combustion or “explosion” into rotary force used to propel the vehicle. There are several types of internal combustion engines: two and four cycle reciprocating piston engines, gas turbines, free piston, and rotary combustion engines. The four cycle reciprocating engine has been refined to such a degree that it has almost complete dominance in the automotive field.
The engine is the heart of the automobile. It converts fuel into the energy that powers the automobile. To operate, it requires clean air for the fuel, water for cooling, electricity (which it generates) for igniting the fuel, and oil for lubrication. A battery and electric starter get it going.
Each “cylinder” of the typical car engine has a “piston” which moves back and forth within the cylinder (this is called “reciprocating”). Each piston is connected to the “crankshaft” by means of a link known as a “connecting rod”.
Four-stroke Piston Cycle
In 1876, a German engineer named Dr. Otto produced an engine, that worked using the four-stroke, or Otto cycle. “Four-stroke” refers to the number of piston strokes required to complete a cycle (a cycle being a sequence of constantly repeated operations). It takes two complete revolutions of the crankshaft to complete the cycle.
The first stroke is the intake stroke. The piston moves down the cylinder and creates a partial vacuum in the cylinder. A mixture of air and fuel is forced through the inlet valve into the cylinder by atmospheric pressure, now greater than the pressure in the cylinder. During this stroke, the exhaust valve stays closed.
The second stroke is the compression stroke. The piston moves up in the cylinder with both valves closed. The air and fuel mixture is compressed and the pressure rises.
The third stroke is the power stroke. Near the end of the compression stroke, the air and fuel mixture is ignited by an electric spark from the spark plug. The combustion that occurs causes a rise in temperature and enough pressure to force the piston down again.
On the fourth stroke, or exhaust stroke, the piston moves up again and forces the burned gases out of the cylinder and into the exhaust system. This cycle repeats itself the entire time the engine is running.
Horsepower is a unit of power for measuring the rate at which a device can perform mechanical work. Its abbreviation is hp or bhp (for brake horse power). One horsepower was defined as the amount of power needed to lift 33,000 pounds one foot in one minute.
Gaskets and seals are needed in your engine to make the machined joints snug, and to prevent fluids and gasses (oil, gasoline, coolant, fuel vapor, exhaust, etc.) from leaking.
The cylinder head has to keep the water in the cooling system at the same time as it contains the combustion pressure. Gaskets made of steel, copper and asbestos are used between the cylinder head and engine block. Because the engine expands and contracts with heating and cooling, it is easy for joints to leak, so the gaskets have to be soft and “springy” enough to adapt to expansion and contraction. They also have to make up for any irregularities in the connecting parts.
Overhead Camshaft (OHC)
Some engines have the camshaft mounted above, or over, the cylinder head instead of inside the block (OHC “overhead camshaft” engines). This arrangement has the advantage of eliminating the added weight of the rocker arms and push rods; this weight can sometimes make the valves “float” when you are moving at high speeds. The rocker arm setup is operated by the camshaft lobe rubbing directly on the rocker. Stem to rocker clearance is maintained with a hydraulic valve lash adjuster for “zero” clearance.
The overhead camshaft is also something that we think of as a relatively new development, but it’s not. In 1898 the Wilkinson Motor Car Company introduced the same feature on a car.
Double Overhead Camshaft (DOHC)
The double overhead cam shaft (DOHC) is the same as the overhead camshaft, except that there are two camshafts instead of one.
Overhead Valve (OHV)
In an overhead valve (OHV) engine, the valves are mounted in the cylinder head, above the combustion chamber. Usually this type of engine has the camshaft mounted in the cylinder block, and the valves are opened and closed by push rods.
All engines have more than one valve; “multivalve” refers to the fact that this type of engine has more than one exhaust or intake valve per cylinder.
Timing refers to the delivery of the ignition spark, or the opening and closing of the engine valves, depending on the piston’s position, for the power stroke. The timing chain is driven by a sprocket on the crankshaft and also drives the camshaft sprocket.
Vacuum System (Importance of)
Engines run on a vacuum system. A vacuum exists in an area where the pressure is lower than the atmosphere outside of it. Reducing the pressure inside of something causes suction. For example, when you drink soda through a straw, the atmospheric pressure in the air pushes down on your soda and pushes it up into your mouth. The same principal applies to your engine. When the piston travels down in the cylinder it lowers the atmospheric pressure in the cylinder and forms a vacuum. This vacuum is used to draw in the air and fuel mixture for combustion. The vacuum created in your engine not only pulls the fuel into the combustion chamber, it also serves many other functions.
The running engine causes the carburetor and the intake manifold to produce “vacuum power,” which is harnessed for the operation of several other devices.
Vacuum is used in the ignition-distributor vacuum-advance mechanism. At part throttle, the vacuum causes the spark to give thinner mixtures more time to burn.
The positive crankcase ventilating system (PCV) uses the vacuum to remove vapor and exhaust gases from the crankcase.
The vapor recovery system uses the vacuum to trap fuel from the carburetor float bowl and fuel tank in a canister. Starting the engine causes the vacuum port in the canister to pull fresh air into the canister to clean out the trapped fuel vapor.
Vacuum from the intake manifold creates the heated air system that helps to warm up your carburetor when it’s cold.
The EGR valve (exhaust-gas recirculation system) works, because of vacuum, to reduce pollutants produced by the engine.
Many air conditioning systems use the vacuum from the intake manifold to open and close air-conditioner doors to produce the heated air and cooled air required inside your vehicle.
Intake manifold vacuum also is used for the braking effort in power brakes. When you push the brake pedal down, a valve lets the vacuum into one section of the power-brake unit. The atmospheric pressure moves a piston or diaphragm to provide the braking action.
The combustion chamber is where the air-fuel mixture is burned. The location of the combustion chamber is the area between the top of the piston at what is known as TDC (top dead center) and the cylinder head. TDC is the piston’s position when it has reached the top of the cylinder, and the center line of the connecting rod is parallel to the cylinder walls.
The two most commonly used types of combustion chamber are the hemispherical and the wedge shape combustion chambers.
The hemispherical type is so named because it resembles a hemisphere. It is compact and allows high compression with a minimum of detonation. The valves are placed on two planes, enabling the use of larger valves. This improves “breathing” in the combustion chamber. This type of chamber loses a little less heat than other types. Because the hemispherical combustion chamber is so efficient, it is often used, even though it costs more to produce.
The wedge type combustion chamber resembles a wedge in shape. It is part of the cylinder head. It is also very efficient, and more easily and cheaply produced than the hemispherical type.
Cutaway of the V-8 Engine
This diagram shows the flow of fuel and exhaust within a V8 engine. It shows the timing chain (driven by the crankshaft) drives the camshaft, which opens the valves. Fuel enters the cylinders via the intake manifold. The spark-caused explosions force the pistons down. Rotation of the crank forces the pistons back up, which expels the exhaust.
A cylinder is a round hole through the block, bored to receive a piston. All automobile engines, whether water-cooled or air-cooled, four cycle or two cycle, have more than one cylinder. These multiple cylinders are arranged in-line, opposed, or in a V. Engines for other purposes, such as aviation, are arranged in other assorted forms.
The diameter of the cylinder is called the “bore” while its height is called its “stroke.” The “displacement” of an engine is actually a reflection of the total amount of volume of the engine’s cylinders, and nothing to do with the actual size of the engine itself (although the two are highly correlated). The displacement is simply the bore multiplied by the stroke of a single cylinder, multiplied by the total number of cylinders in the engine. Muscle car engine displacements were usually measured in cubic inches, while modern vehicle’s are expressed in terms of liters. Roughly 61 cubic inches equals a liter of displacement. Therefore, an engine with 350 cubic inches of displacement would be the equivalent of 5.7 liters.
The Piston, Rings, and Wrist Pin
The piston converts the potential energy of the fuel, into the kinetic energy that turns the crankshaft. The piston is a cylindrical shaped hollow part that moves up and down inside the engine’s cylinder. It has grooves around its perimeter near the top where rings are placed. The piston fits snugly in the cylinder. The piston rings are used to ensure a snug “air tight” fit.
The piston requires four strokes (two up and two down) to do its job. The first is the intake stroke. This is a downward stroke to fill the cylinder with a fuel and air mixture. The second is an upward stroke to compress the mixture. Right before the piston reaches its maximum height in the cylinder, the spark plug fires and ignites the fuel. This action causes the piston to make its third stroke (downward). The third stroke is the power stroke; it is this stroke that powers the engine. On the fourth stroke, the burned gases are sent out through the exhaust system.
The wrist pin connects the piston to the connecting rod. The connecting rod comes up through the bottom of the piston. The wrist pin is inserted into a hole (about half way up) that goes through the side of the piston, where it is attached to the connecting rod.
Pistons are made of aluminum, because it is light and a good heat conductor. Pistons perform several functions. Pistons transmit the driving force of combustion to the crankshaft. This causes the crankshaft to rotate. The piston also acts as a moveable gas-tight plug that keeps the combustion in the cylinder. The piston acts as a bearing for the small end of the connecting-rod. Its toughest job isto get rid of some of the heat from combustion, and send it elsewhere.
The piston head or “crown” is the top surface against which the explosive force is exerted. It may be flat, concave, convex or any one of a great variety of shapes to promote turbulence or help control combustion. In some, a narrow groove is cut into the piston above the top ring to serve as a “heat dam” to reduce the amount of heat reaching the top ring.
For an engine to make more power, it has to take in more air. In most four stroke engines, the air must enter the combustion chamber through the valves. The camshaft controls the opening and closing of the valves by regulating the time that the valve is opened and closed, and how much the valve is opened by. An easy solution to have more power, would be to alter the characteristcs of the camshaft so that it either keeps the valves open for a longer period of time, or lift the valve higher off it’s seat so that more air can pass into the combustion chamber. It all sounds very easy, but once again, there’s more to it than meets the eye. Like most engine mods, this one is also a compromise.
In the perfect engine, the inlet valve will open when the piston is at TDC (top dead center), and as it travels down the bore, it will suck in a full charge equal to it’s displacement. The exhaust valve would open at BDC (bottom dead center), and the full displacement of spent gasses would be pumped out of the engine – the perfect engine running at 100% volumetric efficiency. In practice, the stresses on the valvetrain would just be too much for the materials to handle. To lift a valve of say 50g some 10mm off it’s seat in less than a millisecond (at 6000rpm) without it bouncing or doing anything untoward in the next 100,000 miles of it’s life, simply doesn’t work with the materials in use today. So, the manufacturers used their multi-million dollar research budgets to come up with a simple solution.
The piston travels rather slowly at TDC compared to the middle of the stroke – there’s not much of the pumping action being done in the 10 or 20 degrees around TDC. So, they start to open the valve gently while the piston is still on it’s way up on the exhaust stroke. Although this creates valve “overlap” (time in which both the intake and the exhaust valves are open), it does allow the engine to breathe better and create more power.
When the time that the inlet valve stays open is made longer, the overlap starts to become a problem at low engine speed. The exhaust gasses get pumped into the inlet tracts, substantially diluting the incoming charge and causing the engine to run very poor. That’s why an engine with a wild camshaft runs uneven at idle – it’s choking in it’s own exhaust gasses. However, when the engine speed goes up, the exhaust gasses pick up momentum, and during the overlap period, the departing exhaust charge creates a partial vacuum behind it, sucking in more of the fresh intake charge.
This leads us to two important conclusions:
Firstly, the wilder the camshaft, the less power the engine will make at low rpm. Such wild engines will normally not have enough power at regular “civilized” driving speeds to pull the skin off a rotten banana. To pull away from a stop, you will have to rev it up to come “on the cam”, or stall the engine at every attempt at a civilized getaway. Secondly, the engine will only produce more power at the very top of it’s rev range. These are important points to consider when choosing a racy camshaft for your engine. Are you willing to sacrifice low speed drivability in exchange for more top end power? It’s up to you to decide.
No, we are not against performance camshafts. We have owned several “hairy” cammed cars, and want to point out the facts to you so you won’t end up wit a car you hate. Driving such a car to work every day soon starts to get on one’s nerves. And if you transport passengers in your vehicle, be warned : they are usually not very sympathetic towards the neck-wrenching style of driving that such a vehicle demands to keep it “on the boil”. If you do decide to go with a hairy cam, there are a few things you can do to slightly alleviate the associated low speed problems.
1. A good free-flow extractor exhaust with long primary pipes tuned to low engine speed optimisation can make the engine come on the cam a little sooner. The long 4-into-1 systems seem to be able to “pull the engine on the cam” a little sooner than the regular banana style 4-into-2-into-1 systems.
2. Long ramstacks on the intake. A ram stack are those shiny flared tubes you often see on the carburettors of high-performance engines. These artificially create a longer intake path for the air, allowing it to build up some momentum. They also have an added benefit that they can allow up to 8% more flow into the carb when compared to the usually blunt ending of the carb mouth.
3. Proper gas-flowing of the cylinder head. A lot of cylinder heads out there flow more air in the wrong direction than they can flow in the right direction. Most people who gasflow cylinder heads don’t even realize that they are making it easier for the gasses to also flow well in the wrong direction! Remember that the main problem is that the exhaust gasses flow into the intake port during the increased overlap period. We can put you in touch with people who can do special things to a cylinder head so that it is difficult for the exhaust gasses to pop out through the intake port in the camshafts’ overlap period. There’s a whole science behind optimising the head to make it “cam-friendly”, and usually there is a substantial improvement in the low speed range if the cylinder head is flowed properly, by a person who knows what directional flowing is about. Note that it is easy – even for experienced “port grinders” – to completely ruin the reverse-flow characteristics of your cylinder head.
4. Match the engine controls to the camshaft. The different profile of the camshaft plays havoc with the fuel injection’s standard factory mapping. The ignition timing and mixture requirements of the engine is vastly different to that of a standard engine. The way we would recommend to do this, is to fit a UNICHIP. The engine can be run on a loading type dynamometer, and the engine management system can be reprofiled to match the specific engine’s state of tune. The unichip is perfect for modified engines, because of it’s ability to be reprogrammed whenever needed, i.e. if you decide to make more mod’s, you simply have the unichip reprogrammed to match your new requirements. You don’t have to throw it away like a conventional, old style “chip”.
A recent development is the serpentine belt, so named because they wind around all of the pulleys driven by the crankshaft pulley. This design saves space, but if it breaks, everything it drives comes to a stop.
The automobile engine uses a metal timing chain, or a flexible toothed timing belt to rotate the camshaft. The timing chain/belt is driven by the crankshaft. The timing chain, or timing belt is used to “time” the opening and closing of the valves. The camshaft rotates once for every two rotations of the crankshaft.
The Cylinder Head
The cylinder head is the metal part of the engine that encloses and covers the cylinders. Bolted on to the top of the block, the cylinder head contains combustion chambers, water jackets and valves (in overhead-valve engines). The head gasket seals the passages within the head-block connection, and seals the cylinders as well.
Push Rods attach the valve lifter to the rocker arm. Through their centers, oil is pumped to lubricate the valves and rocker arms.
The flywheel is a fairly large wheel that is connected to the crankshaft. It provides the momentum to keep the crankshaft turning without the application of power. It does this by storing some of the energy generated during the power stroke. Then it uses some of this energy to drive the crankshaft, connecting rods and pistons during the three idle strokes of the 4-stroke cycle. This makes for a smooth engine speed. The flywheel forms one surface of the clutch and is the base for the ring gear.
Harmonic Balancer (Vibration Damper)
The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes “torsional vibration.” To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft that’s causing all the trouble. The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both.
When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can’t speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.
The crankshaft converts the up and down (reciprocating) motion of the pistons into a turning (rotary) motion. It provides the turning motion for the wheels. The crankshaft is usually either alloy steel or cast iron. The crankshaft is connected to the pistons by the connecting-rods.
Some parts of the shaft do not move up and down; they rotate in the stationary main bearings. These parts are known as journals. There are usually three journals in a four cylinder engine.
The crankshaft is held in place by a series of main bearings. The largest number of main bearings a crankshaft can have is one more than the number of cylinders, but it can have one less bearing than the number of cylinders.
Not only do the bearings support the crankshaft, but one bearing must control the forward-backward movement of the crankshaft. This bearing rubs against a ground surface of the main journal, and is called the “thrust bearing.”
The connecting rod links the piston to the crankshaft. The upper end has a hole in it for the piston wrist pin and the lower end (big end) attaches to the crankshaft. Connecting rods are usually made of alloy steel, although some are made of aluminum.
Connecting Rod Bearings
Connecting rod bearings are inserts that fit into the connecting rod’s lower end and ride on the journals of the crankshaft.
Factory RPM Range
Note the reference to factory RPM range. This is an extremely important concept, and must be clearly understood before starting your improvement project. The factory engines were designed and built to run in a specific RPM range. Their parts were of sufficient quality to run almost indefinitely if the RPM limits were observed. The engines developed maximum power throughout the intended range with the heads, manifolds, cams, and manifolds that were installed. For example, most standard production cars used a large two barrel carb., an #066 cam (also called a #4 in the earlier versions), which is 204 degrees intake duration at .050, and ordinary heads with press-in studs, but having very good low and mid-lift air flow. This combination provides extremely strong low and mid range torque which is exactly what the larger cars with high gears need for good throttle feel and quick response. This type of engine doesn’t develop high horsepower because it will not run much past 4600-4800 RPM and can’t breath enough air at high RPM, but it does develop excellent torque from idle up, and essentially the same total amount of torque as the highest HP engines of the same displacement. The Ram Air IV engine was designed to run to a higher RPM of about 5900. This required more air flow into the engine at higher RPM—thus, the higher flowing heads were incorporated. A longer duration cam was needed to give the cylinders time to fill at the higher RPM. The longer duration cam causes the intake valve to close later in the intake cycle, and this in turn, required more compression. The longer duration cam kills the low RPM power while hopefully extending the upper RPM power. With very poor low end power, a lower rear end gear was needed to provide some semblance of low speed performance. As the engine was so weak at low RPM, power steering and air conditioning were not available, and the engine was available only in the lightest body style vehicles. The result was a higher RPM engine with excellent power from about 3000 to 6000 RPM. This is great for a lighter weight car with a 4-speed, or an automatic with a loose converter for drag racing but it would be a dog in a normal weight street vehicle that needs to be driven from stop light to stop light.
So what is the answer for real performance increase? First, determine what RPM range you actually need and intend to use. If you plan to drive the car for some normal transportation, any idle speed over about 650 RPM will be a constant pain with stock converters. If you want good power and throttle response from idle to 3000 RPM (about 70-75 MPH in high gear), don’t install a cam with more than about 210-215 degrees intake duration as measured at .050 lift. Similarly, don’t install a single plane manifold or a carb larger than 750 CFM (except for an 800 Q-Jet) on this type of vehicle. Be wary of the “Performer RPM” manifold, even though it is a dual plane. It definitely degrades low end power, and only begins to help at around 5400 RPM and up. Remember that low-end power is relative to the size/torque of an engine, and that a 455 will have relatively good low-end with an “RPM” but it will still lose power from idle to about 2000 with it! By staying in the factory intended RPM range, your rods, rod bolts, pistons crank, and oil pump are totally satisfactory for any performance use (assuming they are in normal factory condition). The heads, regardless of type, should have first quality valve guides, a valve seat preparation that optimizes low lift air flow, and matching valves. The exhaust seats do not need to be hardened, because you will never load the engine hard enough for a long enough period of time to damage the seats. Even if you somehow manage to do so, this is not a catastrophic event, and the seats could be changed later if needed.
After you have determined what RPM range you expect to use, plan accordingly If you will run higher RPM than your present engine was designed for, consider what changes will be needed. If you are thinking of building a race engine, you may need special rods, forged and/or lightened pistons, vastly improved air flow through your heads, a poorer idling cam, higher performance manifold and headers. If you are thinking an engine for race and street, all the stock internal parts are totally satisfactory. “Hotter” ignition systems or components will not improve performance over properly operating factory systems. The factory Q-Jet manifold and carb are adequate and actually superior to any aftermarket setups you can buy. The factory ignition points type or HEI, will easily do the job, although the points system must be properly adjusted and maintained. Stock exhaust or Ram Air type manifolds will work fine, and headers with 1-5/8″ or 1-3/4″ primary tubes can be used if you want to put up with the hassle of leakage, additional noise, poor ground clearance, difficult installation and high maintenance.
There are various methods of increasing engine RPM capability. However, increased RPM does not automatically improve acceleration. Each vehicle has unique gearing, weight, and engine power range. For optimum acceleration, the engine should be operated such that it stays in its fattest power band through each gear. For example, if the engine makes good power from 3200 to 5000, it makes no sense to shift at 5500 because you not only lose acceleration from the 5000 to 5500 range, but when you shift to the next gear, the engine will only drop to about 3500, thus losing the power from 3000 to 3500. Regardless of your engine characteristics, you must try shifting at various RPM points to find the best overall point for your combination.
Disconnecting the alternator will not usually make a measurable difference in acceleration. The normal electrical load without lights and fans is about 4 amps (for ignition system) and that represents less than 1/4 HP load on the engine. However, disconnecting the alternator drops the available voltage from the nominal 14 to the ambient battery voltage of 12.4. That represents a loss of 11% of available voltage for the ignition, and the high voltage to the plugs will drop by about the same percentage. The disconnect exercise may appear to pay off if the vehicle is run first with the alternator disconnected, and then with it reconnected. Running without the alternator discharges the battery, and when it is reconnected, the alternator will charge as much as 35 amps to recharge the battery, as well as affect the engine. However, testing in the correct sequence will reveal no gain and possibly a loss in acceleration due to the reduction of the high voltage to the plugs.
Removing the power steering belt will usually help by several hundredths in the quarter mile. Theoretically, this should not help because there is little if any load on the steering pump while running straight ahead. Apparently, the combination of belt tension and the larger and heavier pump pulley do present a noticeable acceleration load on the engine. The only downside to removing the belt is the harder steering.