Efi Ignition
Efi Ignition Do Electronic Fuel Ignition Engines (EFI) Have to be "tuned up?" If NOT, then, why? DOES THE TIMING HAVE TO BE SET ON AN EFI ENGINE? Yes. And, No. But first, EFI refers to fuel IN...
Efi Ignition
 Do Electronic Fuel Ignition Engines (EFI) Have to be "tuned up?" If NOT, then, why? DOES THE TIMING HAVE TO BE SET ON AN EFI ENGINE? Yes. And, No. But first, EFI refers to fuel INJECTION, not ignition. Even so, the question and general answer as to the contribution of electronics to engine performance is a good one. A tune-up, in days of old, generally referred to the car's ignition system, including a mysterious thing called "timing," which is to say the relationship between the physical position of the power-plant components (pistons, valves) and the occurrence of the spark from the sparkplug. The idea was to make the spark fire off at precisely the moment the piston had moved all the way up inside the cylinder -compressing the fuel air mix- just at the point it was ready to start down again in the "power stroke" caused by igniting the fuel-air mix in the top of the cylinder. Ignite the mixture too SOON, and there is a loss of power because the piston hasn't gotten all the way up there yet; ignite it too LATE and there is a loss of power because of less compression -the space for the explosing fuel/air mix is too big, so you won't get a full power . And in BOTH cases, you have "rough running," poor fuel economy and dirty cylinders and valves (the things that let fuel and air into the cylinders) because of incomplete combustion of the fuel. If you're old enough to remember the mechanic working on your old heap, or your older brother working on his, or the 18 year old down the street with his head under the hood of the souped-up '38 Pontiac decorated with speeding tickets along the headliner, then you may also remember a special light that they pointed at the rim of flywheel as they tuned the car. The light was pointed at a mark (usually made with a yellow crayon) on the flywheel, and flickered on and off as the mechanic made adjustments to various controls in the ignition system. If you actually looked in there, you'd see the yellow mark move ahead or move backwards, sort of like looking at the spokes on a wheel appear to move backwards even though the wheel is moving forwards. The light was turned off and on by the pulses of electricity being sent to the spark plugs, so that when it was on, a spark had just been fired inside the cylinder. Of course, the engine is turning pretty fast, even when idling, so it was a sort of "strobe effect." Anyway, once the "timing mark" seemed to stand still in the flickering light, everything was timed right. The ignition system in an old style car like that included mechanical and electronic parts that would wear out, or go out of adjustment simply from being used. These included: The distributor, which was a hollow, cylindrical thick plastic container with nipples at the top to which were attached the spark plug cables. Inside the distributor was a "rotor," another piece of thick "plastic" mounted on a shaft in somewhat the same way the needle on a compass is mounted. On the bottom of the rotor and at each end was a disc of metal, about as big as the head of a thumb-tack. Near the perimeter and on the bottom of the distributor was a circle of similar thumb-tack heads. There was one contactor for each spark plug. The disc on the rotor would contact each of these in turn as it spun inside the distributor body, picking up electricity to send to the spark plugs. COMPLETELY mechanical! And the whole thing was powered by a small linkage to the engine itself. The other major part was a "capacitor," a small metal can (about the size of a 35 MM film canister) with wires coming out of it. And that was the only "electronic" part of the ignition system. A capacitor is a sort of short-lived battery, which holds a big jolt of electricity for a moment, then discharges it in a split second - BANG! So it was being charged and discharged as everything rotated, sending jolts of electricity down to the spark plugs. And so, the "tune-up," usually involved replacing all or some of these parts so that everything was back to "no wear and tear" status. Usually, the air filter and oil filter was also changed at this time, and often the sparkplugs, the idea being to bring everything up to optimum performance before tuning the engine. The last step was "timing," to get all the parts working together "in sync." Until next time -usually 6 months down the road, so to speak. And all of this applies to the "ignition system." That is, every bit of it has to do with making the gasoline ignite at just the right moment. So, ignition applies to a great deal more than just turning the key. In fact, all the key does is switch on a small electric motor (powered by your battery) to make the engine turn over. Once it "catches," the ignition is an entirely self-working process. But suppose you could get RID of all that mechanical stuff? Suppose there was a way for the engine to "tune itself?" THAT'S where the "EFI" comes in. The move to EFI was inspired in great part by -are you ready for this? -our Arabian friends! That's right: the oil crisis of the '70's and Federal fuel economy legislation that followed encouraged auto makers to make more fuel efficient vehicles. At the same time, auotmakers were also responding to pressure to lower vehicle emmissions to clean up the air. In both cases, you need to know more about what's going on inside the engine if you want it to run better and cleaner. AND -at about the same time- advances in electronics and onboard monitoring and computing systems, spawned in part by the space program, were coming into the market place -and a decent price. And THUS, the auto industry had both the motive and the means to improve fuel economy, vehicle emissions, and power-to-weight engine characteristics pretty much all at the same time. EFI was an early adaptation. Sensor data about engine performance could be used to make the engine adjust itself according to conditions and according to wear and tear in the engine itself. All of that is done with electronic parts -circuit boards and little computers that figure it all out in real time as the vehicle is being operated. And this includes metering the gas going to the engine -the fuel "injection" part. Old style cars used "carburators" to do the job -mechanical systems that fed gas in gulps pretty much in response to the gas pedal. These were replaced with "throttle bodies" that used some electronic control, and finally by fuel injection, which blends together the driver's demand for acceleration and current operating conditions to figure out the best mix. And so, the old mechanical parts are history. Electronic components don't "wear out" the way mechanical ones do, because they don't move or have any friction. Consequently, the tune-up is a thing of the past. Obviously, there can be conditions that the system can't handle, such as failure of a sensor, or serious engine failure that can't be corrected by self-adjustment. But the system, while it can't FIX the problem, often knows what the problem is. It logs it into memory, so the mechanic can attach a system to learn what the engine is reporting about itself. If you have abuddy who is a mechanic, he'she may show you how you can do it YOURSELF by pushing some buttons in the car. What you'll get are codes that match up to various problems. Otherwise, when you see the "Check Engine Soon" light comes on -do what it says -check it SOON. All of this electronic capability leaves out one key element of the ignition system that's STILL there -the sparkplugs! While they don't "move," they do sustain millions of bursts of electricity, each one actually being, in effect, a tiny arc-welder. Over time, that means the plugs will wear out or stop working. But now, that's a much longer period of time because the engine runs cleaner and more consistently. And, the plugs themselves have been re-engineered to last 100,000 miles or more. I've not changed one yet in my '03 Chevy, which has over 150,000 miles on it, runs like a dream and gets a clean bill of health whenever its in for some other service -such as power windows that stop working. That said, at some point you may need to replace your plugs or cables, but very infrequently and maybe never. This is very much like modern medicine. Medical advances have eliminated or decreased to lethality of certain diseases realted to the heart, for example. So now, many people will die of something related more to the aging process than to the action of disease itself. Likewise your car. It may rust out before it needs a tune up. I hope this helps. A fun question! |
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Supercharger FAQ
Why has supercharging become so popular?
There are a number of reasons. First, an efficient supercharger system can produce yesterday's musclecar performance using today's low-octane gasoline, with exceptional reliability and minimal impact upon fuel economy. Second, superchargers have developed to the point that they are easy to install and simple to maintain, especially when compared to pulling, rebuilding and fine-tuning an engine. Finally, unlike nitrous oxide, which requires frequent repurchase of fuel, once a supercharger is installed there is no more expense or hassle associated with performance. In short, supercharging delivers exceptional performance with little of the hassles traditionally associated with high performance. Centrifugal supercharging is the only way to make a reliable 500, 600, 700+ horsepower on otherwise stock, daily driven V-8's.
How does supercharging increase engine performance?
Superchargers achieve performance gains by increasing the density of the air/fuel charge within the combustion chambers of an engine. This increase in density is achieved by forcing additional amounts of air (beyond the amount of air that normal atmospheric pressure would force into the engine) at the lowest temperature possible. CFM measures the volume of air that an engine is flowing, while MAF (mass air flow) also factors in the temperature of the air charge, since a cooler charge is more dense and therefore more powerful. So in more technical terms, supercharging increases both the volumetric efficiency of the engine and the mass air flow through the engine to produce gains in both horsepower and torque.
How much horsepower will a supercharger add to my engine?
Although some manufacturers claim a specific horsepower increase, superchargers actually add horsepower as a percentage gain (percentage of an atmosphere). Assuming an engine with a compression ratio of around 9:1 running pump gas,if a supercharger gives your engine 14.7 psi of boost (another atmosphere) that will essentially double the output of your engine, everything else being equal. After adjusting for thermal and mechanical energy transfer, if an efficient centrifugal supercharger is generating 7.5 psi (approx. 1/2 an atmosphere), you will see around a 35-40% gain in horsepower and torque at your non-supercharged maximum horsepower rpm. If detonation forces you to use an ignition/timing retard system, you will of course see less of a gain because backing off several degrees of timing will greatly reduce an engine's power output. At higher boost levels, the heat generated by compressing air will produce diminishing returns as the boost is increased, although the use of intercooling or racing fuel can avoid this scenario of diminishing returns. Assuming the use of intercooling to run higher boost levels while maintaining reliability, a 100% increase can generally be achieved at around 17 psi on an engine with 9:1 compression running pump gas.
What type of fuel do I need with a supercharged automotive or truck engine?
The primary issues that determine the type of fuel needed are whether the engine is fuel-injected or carbureted, the compression ratio of the engine, and whether or not the supercharger system is intercooled.
For Intercooled ProCharger EFI/TPI applications with compression ratios less than 9.5:1, boost levels of 14-17 psi can be safely run with full timing on pump gas, and will produce horsepower gains of 75-100% (depending upon the boost level and the motor specifications). For 9.5:1 EFI/TPI applications running without an intercooler, boost levels above 5 psi will require the use of ignition/timing retard on pump gas, and will produce horsepower gains of 35-45%. Boost levels above 12 psi should generally be avoided even with racing fuel on a 9.5:1 motor. Of course, lower compression motors will be able to run more boost, and higher compression motors should run less boost, everything else being equal.
For carbureted motors, the rules are slightly different. Carburetors deliver the vast majority of fuel in a liquid state, and as this raw fuel atomizes from liquid to gas, a chemical state change actually occurs. Due to this endothermic reaction, which draws heat and cools the incoming air, a carbureted motor can safely handle more boost than a comparable EFI/TPI motor. For carbureted engines with compression ratios of 9:1 or less and boost levels in the 8-14 psi range, pump gasoline works very well. Compression ratios of 10:1 and higher require lower boost levels, higher octane fuel, intercooling, or some combination of the above. Compression ratios in the 7or 8:1 range can usually handle 12-20 psi on pump gasoline.
What is detonation, and how can it be controlled?
Detonation, or engine knock, occurs simply when fuel pre-ignites before the piston reaches scheduled spark ignition. This means that a powerful explosion is trying to expand a cylinder chamber that is shrinking in size, attempting to reverse the direction of the piston and the engine. When detonation occurs, the internal pneumatic forces can actually exceed 10x the normal forces acting upon a properly operating high performance engine. Detonation is generally caused by excessive heat, excessive cylinder pressure, improper ignition timing, inadequate fuel octane or a combination of these. Of the previous, excessive heat is usually the culprit. As an engine is modified to generate more power, additional heat is produced. Today's pump gas will only tolerate a finite amount of heat before it pre-ignites and causes detonation. Although forced induction engines usually produce far less heat than comparable naturally aspirated high compression engines, the cylinder temperatures in intercooled engines are radically cooler yet. It is rarely boost that causes detonation, just unnecessary heat. An intercooler is such a natural solution for forced induction, that in almost every sophisticated application, intercooling is part of the package.
For engines that are experiencing detonation problems, the primary options are the use of ignition/timing retard systems, higher octane fuel, or intercooling. While ignition retard systems can be helpful in certain situations, they can also greatly reduce the horsepower output of an engine, as any reduction in timing will reduce horsepower. And while a reduction in timing can save a motor from detonation, the excessive heat which was causing the detonation is still present. Intercooling, on the other hand, actually removes the heat which causes detonation, and allows higher boost levels to be safely run with full timing on pump gas. This produces the maximum benefit in terms of both horsepower gains and engine protection, without any additional maintenance or hassle.
How will a supercharger affect my fuel economy?
Although roots superchargers have significant parasitic load and do dramatically decrease fuel economy, centrifugal superchargers will yield approximately the same fuel economy as normally aspirated engines, under normal throttle conditions. When racing, however, fuel enconomy will decrease given the supercharged engine's ability to consume additional fuel and produce additional horsepower.
Will a supercharger shorten the life of my engine or drivetrain?
That is a very subjective question, as the manner in which an automobile is driven directly affects engine life. Assuming a properly tuned system, proper oil change and engine maintenance, and similar driving, supercharging generally will not shorten the life of an engine, just as is the case with OEM turbocharging (with proper cooldown for turbochargers. A cooldown period after driving is not necessary with supercharging). This is especially true of centrifugal supercharging, which generates boost in line with engine rpm, unlike roots and twin screw blowers, whose low rpm boost can place additional strain on the engine and drive train.
Superchargers can be used with automatic or manual transmissions and will not increase transmission wear under normal driving. When racing, however, the additional torque provided by supercharging will place additional load on the transmission, especially when increased traction is present, such as with slicks. This impact is minimized when the boost increases with engine rpm, as is the case with centrifugal supercharging and turbocharging.
What is the difference between Supercharging and Turbocharging?
A supercharger is a mechanically driven air pump that is connected directly to the engine crankshaft via the serpentine belt. A turbocharger is driven by the flow of exhaust gas which is generated as part of the engine combustion cycle.
Why choose Supercharging over Turbocharging?
Because turbochargers depend on the energy in the exhaust gas stream to spool up and generate boost pressure, there is often a delay in the response of the engine at lower engine speeds where exhaust energy is lower. This delay is often referred to as “Turbo Lag”. On the other hand, a supercharger is directly driven by the crankshaft of the engine, and there is no delay in engine response at lower engine speeds. This allows supercharged engines to have instant throttle response and better vehicle driveability.
If more air is pumped into the engine, then more fuel must be used also…Doesn’t this mean less fuel economy?
If a supercharged 3.8L V6 is compared to a naturally aspirated 3.8L V6, the supercharged V6 does use slightly more fuel. However, the power and performance of the supercharged V6 is comparable to a larger V8 which uses much more fuel to achieve the same performance.
Does the Supercharger provide boost at all times?
No. Under cruising conditions, the compressed air from the supercharger is bypassed, and is recirculated in the supercharger, improving fuel efficiency. Under acceleration, the bypass is closed, and the “boosted” air is sent into the engine to provide increased response and power.
How reliable are supercharged engines?
General Motors has been offering a supercharged version of the 3800 V6 engine since 1991. The Supercharged 3800 Series II engine has one of the best warranty ratings amongst all of General Motors powertrain offerings. Along with GM, other automakers like Jaguar, Mercedes-Benz, Nissan, BMW-Mini, and Ford all have used superchargers as an effective and reliable alternative to larger, less fuel efficient powertrains on various cars and trucks.
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