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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