Until 1970, high-performance cars often had compression ratios of up to 11 or 12 to one, easily handled with vintage high octane gasolines readily available in the 98–99 ((R+M)/2) range.By 1972, engines were running compression ratios of 8–8.5:1.In the 1980s and 1990s, compression ratios in computer-controlled fuel injected vehicles were again showing up in the9.0–11:1 area based on fuel injection’s ability to support higher compression ratios without detonation, coupled with the precise air/fuel control and catalysts required to keep emissions low. Race car engines typically run even higher compression ratios. In air unlimited engines, maximum compression ratios with gasoline run in the 14–17:1 range. Ratios above 14:1 demand not only extremely high-octane fuel (which might or might not be gasoline), but experienced racers use tricks like uniform coolant temperature around all cylinders, low coolant temperature, and reverse-flow cooling. Extremely high compression ratios also require excellent fuel distribution to all cylinders, retarded timing under maximum power,very rich mixtures, and probably individual cylinder optimization of spark timing, air/fuel ratio, and volumetric efficiency. IS HEALTHY AND TUNABLEPrior to performance tuning, a performance engine must not burn oil, which will tend to act as a pro-knock agent. The engine must have low oil consumption past rings, turbo shaft seals, valvestems, and so on. Obviously, the engine should not be leaking water internally (which would turn oil white), nor should therebe excessive scale in the engine cooling jacket. The motor itself must be mechanically sound, with adequate oil pressure under all circumstances. Most powerful EMSscan monitor oil pressure and sound alarms and take countermeasures to stop the engine if oil pressure drops dangerously low.There are labs with the ability to analyze used engine oil to checkfor abnormal metal content and to analyze the source of abnormal metals, which can be very useful in evaluating internalengine health.If this is a super-duty engine with power-adders, the pistonsshould be thermal-coated, or the engine equipped with oilsquirters, or the rods equipped with an orifice between the bigend at an angle toward the piston wrist pin designed to providea pressurized cooling spray of oil against the undersides of thepistons to cool it.The engine management system and sensors must be working correctly.The external coolant system must have integrity, with theradiator working efficiently. The fans and shroud must be working efficiently, and if the car is on a stationary chassis dyno, therespark advanceSpark advance, which is optimally timed to achieve best torqueby producing peak cylinder pressure at around 15 degrees ATDC,increases octane requirements by a half to three-quarters of anoctane number per degree of advance. Spark advance increasescylinder pressure and allows more time for detonation to occur.Engine speed range and fuel burn characteristics affectignition timing requirements. As an engine turns faster, the sparkplug must fire at an earlier crank position to allow time for agiven air/fuel mixture to ignite and achieve a high burn rate andmaximum cylinder pressure by the time the piston is positionedto produce best torque. This is dependent not only on enginespeed but on mixture flame speed, which, in turn, is dependentnot only on the type of fuel but on operating conditions thatchange dynamically, such as air/fuel mixture.Therefore, an independent variable affecting the need forspark advance as rpm increases is the need to modify ignitiontiming corresponding to engine loading and consequentvolumetric efficiency variations, which demand varying mixtures.Throttle position, for example, affects cylinder filling, resulting incorresponding variations in optimal air/fuel mixture requirements.An important factor that affects VE—and potentially flame speed—is valve timing. Remember, a denser mixture burns more quickly, and a leaner mixture requires more time to burn.Valve timing has a great effect on the speeds at which an engine develops its best power and torque. Adding more lift and intake/exhaust valve overlap allows the engine to breathe more efficiently at high speeds. However, the engine may be hard to start, idle badly, bog on off-idle acceleration, and produce bad low speed torque. This occurs for several reasons. Increased valve overlap allows some exhaust gases still in the cylinder at higher than atmospheric pressure to rush into the intake manifold exactly like EGR, diluting the inlet charge—which continues to occuruntil rpm increases to the point where the overlap interval is so short that reverse pulsing is insignificant. But big cams result ingross exhaust gas dilution of the air/fuel mixture at idle, which consequently burns slowly and requires a lot of spark advance anda mixture as rich as 11.5 to 1 to counteract the lumpy uneven idleresulting from partial burning and misfires on some cycles. Valve overlap also hurts idle and low-speed performance by lowering manifold vacuum. Since the lower atmospheric pressure of high vacuum tends to keep fuel vaporized better, racing cams with low vacuum may have distribution problems and a wandering air/fuel mixture at idle, which may require an overall richer mixture in order to keep the motor from stalling, particularly with wet manifolds. Carbureted vehicles with hot cams may not have enough signal available to pull sufficient mixture through
The idle system, leaning out the mixture, requiring a tuner to increase the idle throttle setting (which may put the off-idle slot/ port in the wrong position, causing an off-idle bog). Obviously, this is not a problem with fuel injection. Short-cam engines may run at stoichiometric mixtures at idle for cleanest exhaust emissions. Beginning with the Acura NSX, some high-performance engines began to make use of a dual-mode cam profile, in which one set of cam lobes is used for low speed conditions and another for high rpm. Coming off idle, a big-cam engine may require mixtures nearly as rich as at idle to eliminate surging, starting at 12.5–13.0 gasoline air/fuel mixtures and leaning out with speed or loading. Mild cams will permit 14.0–15.0 gasoline mixtures in off-idle and slow cruise. With medium speeds and loading, the bad effects of big cams diminish, resulting in less charge dilution, allowing the engine to happily burn gasoline mixtures of 14 to 15:1 and higher. At the leaner end, additional spark advance is required to counteract the slower flame speed of lean mixtures. Hot cams may produce problems for carbureted vehicles when changed engine vacuum causes the power valve to open at the wrong time. Changed vacuum will affect speed-density fuel-injection systems but have no effect on MAF-sensed EFI. Where air/ fuel mixtures are inconsistent or poorly atomized, flammability suffers, affecting many other variables. With a big cam, the spark advance at full throttle can be aggressive and quick; low VE at low rpm results in slow combustion and exhaust dilution, lowering combustion temperatures and reducing the tendency to knock. Part-throttle advance on big-cam engines can also be aggressive due to these same flame speed reductions resulting from exhaust dilution of the inlet charge due to valve overlap. Turbulence and swirl are extremely important factors in flame speed—more important, within limits, than mixture strength or exact fuel composition. Automotive engineers have long made use of induction systems and combustion chamber geometry to induce swirl or turbulence to enhance flame speed and, consequently, anti-knock characteristics of an engine. Wedge head engines, with a large squish area, have long been known to
induce turbulence or swirl as intake gases are forced out of the squish area when the piston approaches top dead center. In the 1970s, automotive engineers began to de-tune engines to meet emissions standards that were increasingly tough. They began to retard the ignition timing at idle, for
example, sometimes locking out vacuum advance in lower gears or during normal operating temperature, allowing more advance if the engine was cold or overheating. Since oxides of nitrogen are formed when free nitrogen combines with oxygen at high temperature and pressure, retarded spark reduces NOx emissions by lowering peak combustion temperature and pressure. This strategy also reduces hydrocarbon emissions. However, retarded spark combustion is less efficient, causing poorer fuel economy, reduced power, and higher heating of the engine block as heat energy escapes through the cylinder walls into the coolant. The cooling system is stressed as it struggles to remove the greater waste
heat during retarded spark conditions, and fuel economy is hurt since some of the fuel is still burning as it blows out the exhaust valve, necessitating richer idle and main jetting to get decent off-idle performance. If the mixture becomes too lean, higher combustion temperatures will defeat the purpose of ignition
or a reasonable idle speed, which, combined with the higher operating temperatures, can lead to dieseling (not a problem in fuel-injected engines, which immediately cut off fuel flow when the key is switched off). By removing pollutants from exhaust gas, three-way catalysts tend to allow more ignition advance at idle
and part throttle. Undesirable products of combustion include formaldehyde, NOx, CO2, and fragments of hydrocarbons. In any case, various high-performance fuels vary in burn characteristics, particularly flammability, flame speed, emissions, and so on, which all affect spark timing requirements. Gasoline
engines converted to run on propane, natural gas, or alcohol require a different timing curve due to variations in combustion flame speed of the air/fuel mixture.
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You are probably taking this course for one of two reasons. Either you are preparing yourself to enter into the field of automotive service, or you are expanding your skills to include automotive electrical systems. In either case, congratulations on selecting one of the most fast-paced segments of the automotive industry. Working with the electrical systems can be challenging, yet very rewarding; however, it can also be very frustrating at times. For many people, learning electrical systems can be a struggle. It is my hope that I am able to present the course to you in such a manner that you will not only understand electrical systems, but will excel at it. There are many ways the theory of electricity can be explained, and many metaphors can be used. Some compare electricity to a water flow, while others explain it in a purely scientific fashion. Everyone learns differently. I am presenting electrical theory in a manner that I hope will be clear and concise. If you do not fully comprehend a concept, then it is important to discuss it with your instructor. Electricity is somewhat abstract; so if you do have questions, be sure to ask me in Udemy ask section.
Why Become an Electrical System Technician?
In the past, it was possible for technicians to work their entire careers and be able to almost completely avoid the vehicle’s electrical systems. They would specialize in engines, steering/ suspension, or brakes. Today, there is not a system on the vehicle that is immune to the role of electrical circuits. Engine controls, electronic suspension systems, and anti-lock brakes are common on today’s vehicles. Even electrical systems that were once thought of as being simple have evolved to computer controls. Headlights are now pulse-width modulated using high side drivers and will automatically brighten and dim based on the light intensity of oncoming traffic. Today’s vehicles are equipped with twenty or more computers, laser-guided cruise control, sonar park assist, infrared climate control, fiber optics, and radio frequency transponders and decoders. Simple systems have become more computers reliant. For example, the horn circuit on the 2008 Chrysler 300C involves three separate control modules to function. Even the tires have computers involved, with the addition of tire pressure monitoring systems!
Today’s technician must possess a full and complete electrical background to be able to succeed. The future will provide great opportunities for those technicians who have prepared themselves properly and learn more with this Car Mechanic Course.
On the off chance that you’re not especially precisely slanted, you might watch the people who are with appreciation, surprise, and irritation since they have something you don’t: a comprehension of how things work and how things fit together. Whenever they dismantle something, they can reassemble it how it was. Whenever they say that they need to investigate the hood, they can really get the darn thing open. Furthermore, when they need to change a level, they don’t endure ten minutes attempting to sort out which end of the raise is.
Fortunately, you don’t need to be brought into the world with a wrench in your grasp to know how to fix things — even things as apparently convoluted as a vehicle. I know; I’ve been there. The Introduction fills you in regarding my car revelation.
The Best Way to Learn Car Repair is start with this Auto Mechanic Course.
Obviously, the easiest errands can once in a while be the greatest obstacles to survive. All things considered, in the event that you couldn’t actually sort out some way to open the hood, how might you check the oil or the coolant level? That is the reason I start this course with the essentials: straightforward positions that you’ll have to do over and over — like opening the hood, lifting a vehicle, and replacing a tire. I likewise incorporate guidelines for filling the gas tank yourself (it’s less expensive than full-administration), a reliable technique for dismantling anything and assembling it back once more, and security pointers that each technician — experienced and amateur — ought to notice.
