Turbochargers and Superchargers
Let's start with the similarities. Both turbochargers and superchargers are called forced induction systems. They compress the air flowing into the engine. The advantage of compressing the air is that it lets the engine stuff more air into a cylinder. More air means that more fuel can be stuffed in, too, so you get more power from each explosion in each cylinder. A turbo/supercharged engine produces more power overall than the same engine without the charging.
The typical boost provided by either a turbocharger or a supercharger is 6 to 8 pounds per square inch (psi). Since normal atmospheric pressure is 14.7 psi at sea level, you can see that you are getting about 50-percent more air into the engine. Therefore, you would expect to get 50-percent more power. It's not perfectly efficient, though, so you might get a 30-percent to 40-percent improvement instead.
The key difference between a turbocharger and a supercharger is its power supply. Something has to supply the power to run the air compressor. In a supercharger, there is a belt that connects directly to the engine. It gets its power the same way that the water pump or alternator does. A turbocharger, on the other hand, gets its power from the exhaust stream. The exhaust runs through a turbine, which in turn spins the compressor.
There are tradeoffs in both systems. In theory, a turbocharger is more efficient because it is using the "wasted" energy in the exhaust stream for its power source. On the other hand, a turbocharger causes some amount of back pressure in the exhaust system and tends to provide less boost until the engine is running at higher RPMs. Superchargers are easier to install but tend to be more expensive.
The Similarities between Superchargers and Turbochargers
Turbochargers and superchargers are similar in that they both compress air to higher than atmospheric pressures. Normal or standard atmospheric pressure is about 14.7 psi (pounds per square inch or "psi"). The job of the compressor common to both turbochargers and superchargers is to increase air pressure so that more air is forced into the cylinders ("forced induction"). This increased air volume ("boost") is mixed with a proportionately increased fuel volume which, when burned in the combustion cycle, results in increased horsepower and torque production.
Power Curve Differences
Because they are belt driven from the engine crankshaft, centrifugal and roots superchargers build boost as rpm increases in a linear fashion. As engine rpm increases, the supercharger compressor speed (and boost level) increases to the point of peak boost occurring at peak engine rpm. For example, a centrifugal or roots supercharger designed to produce 8 psi at 6,000 rpm may produce as little as 2.5 lbs. of boost at 3,000 rpm. Screw-type superchargers are more like turbochargers in that they build boost much earlier than a centrifugal or roots-type, and they are also belt-driven. Turbochargersare exhaust driven, and come up to speed very quickly (almost instantly if properly sized), and will reach the same 8 lb. peak boost level as low as 2,500 rpm. There will always be lag with a turbo system. Small size turbos are good for spooling at lower rpms but the user must utilize a wastegate to slow down the fans when boost gets too high. thus at a higher rpm. smaller turbos loose their appeal. On the other hand, you can use a twin turbo setup with a small and a large turbo mounted and this does well for having boost at all rpms.
Just like the air conditioner compressor on a car, all superchargers, including centrifugal, roots and screw-type, require horsepower to turn them. This "parasitic" drag is always present, even when the car is being driven normally, and can rob 20%-30% of the power being produced by the engine. The result is a significant decrease in fuel economy and less net power produced. Turbochargers, however, are exhaust gas driven and don't require the same parasitic loss to spin the compressor. When driven normally, a turbocharged car will not consume more fuel and, in fact, gas mileage can actually increase. Even when under full throttle, a turbocharger system will produce as much horsepower at 9 psi as a supercharger at 12 psi. Over all though, Superchargers are more reliable than turbos by themselves. This is because of the residual oil that sits inside the bearings can cook due to the high temperatures these turbos operate at; combined with the insane amount of rpms they spin at.
Both superchargers and turbochargers require high compressor rpm to compress the air. This ranges from 30,000-65,000 rpm in superchargers and can be even higher with turbos (over 100,000 rpm). In order to achieve the high rpm levels required to compress the air to the psi required, superchargers must have a step-up mechanism (gears, belts, pulleys or a combination thereof) consisting of numerous moving parts, to convert 6,000 engine rpm to the 40,000+ rpm necessary to build boost. Turbochargers need no step-up mechanism and have only one moving part, the compressor/turbine wheel assembly (see Figure 2). The simplicity of the turbocharger is therefore less prone to mechanical problems. Superchargers must have a belt to drive them, and belt slippage or breakage can be a problem. More serious problems include crankshaft, bearing and engine damage caused by belt tension forces on the crankshaft. Turbochargers have no belt and no direct mechanical connection to the crankshaft, thereby eliminating these problems. It is interesting to note that many automobiles and nearly all large over-the-road trucks use turbochargers that regularly log in excess of a million miles of reliable performance.
Some superchargers have a separate lubricating system that must be maintained and some don’t. Turbochargers are lubricated by the engine oil, but will require tapping the oil pan to install, and require no additional maintenance beyond what is normally required for a naturally aspirated car.
Superchargers are directly connected to the belt drive system, they are always producing some level of boost and cannot be "turned off". Because turbochargers only produce boost when under load (as in full throttle acceleration), performance under normal driving conditions is no different than if the engine were naturally aspirated. Turbocharged cars exhibit excellent drivability characteristics.
Upgradability and Adjustability Comparison
Superchargers are generally not upgradeable. When higher performance is required beyond the capabilities of a specific supercharger system, the entire system must be replaced. Turbocharger systems, however, are usually upgradeable by simply upgrading or installing a larger turbocharger without requiring replacement of the entire system. Further, adjusting the boost levels on a supercharger requires removing and replacing pulleys, idlers and belts. Adjusting the boost levels on a turbocharger may be accomplished as easy as a simple turn of a boost controller knob from the comfort of the inside of the car or without a controller a different spring must be installed in the wastegate.
At first glance, turbo systems may appear to cost more. However, if you consider everything that is included in a complete turbo kit that must be purchased in addition to the supercharger kit in order for the supercharger kit to be comparable (not even considering the performance differences), you may find the turbo system is less expensive and a much better horsepower per dollar value. Depends on your unique setup and what the purpose of your car is to decide on which is a better value.
Because of the few things required, most diy'ers can install a supercharger easily. Turbos require more installation work and also more upgrades to the engines bay. Supercharges on the other hand if not tuned properly can detonate and destroy the top end a lot easier.
Turbo Tech 101 ( Basic )
How a Turbo System Works
Engine power is proportional to the amount of air and fuel that can get into the cylinders. All things being equal, larger engines flow more air and as such will produce more power. If we want our small engine to perform like a big engine, or simply make our bigger engine produce more power, our ultimate objective is to draw more air into the cylinder. By installing a Garrett turbocharger, the power and performance of an engine can be dramatically increased.
So how does a turbocharger get more air into the engine? Let us first look at the schematic below:
1 Compressor Inlet
2 Compressor Discharge
3 Charge air cooler (CAC)
4 Intake Valve
5 Exhaust Valve
6 Turbine Inlet
7 Turbine Discharge
The components that make up a typical turbocharger system are:
The air filter (not shown) through which ambient air passes before entering the compressor (1)
The air is then compressed which raises the air’s density (mass / unit volume) (2)
Many turbocharged engines have a charge air cooler (aka intercooler) (3) that cools the compressed air to further increase its density and to increase resistance to detonation
After passing through the intake manifold (4), the air enters the engine’s cylinders, which contain a fixed volume. Since the air is at elevated density, each cylinder can draw in an increased mass flow rate of air. Higher air mass flow rate allows a higher fuel flow rate (with similar air/fuel ratio). Combusting more fuel results in more power being produced for a given size or displacement
After the fuel is burned in the cylinder it is exhausted during the cylinder’s exhaust stroke in to the exhaust manifold (5)
The high temperature gas then continues on to the turbine (6). The turbine creates backpressure on the engine which means engine exhaust pressure is higher than atmospheric pressure
A pressure and temperature drop occurs (expansion) across the turbine (7), which harnesses the exhaust gas’ energy to provide the power necessary to drive the compressor
What are the components of a turbocharger?
The layout of the turbocharger in a given application is critical to a properly performing system. Intake and exhaust plumbing is often driven primarily by packaging constraints. We will explore exhaust manifolds in more detail in subsequent tutorials; however, it is important to understand the need for a compressor bypass valve (commonly referred to as a Blow-Off valve) on the intake tract and a Wastegates for the exhaust flow.
Blow-Off (Bypass) Valves
The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo’s compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it.
Blow-Off valves use a combination of manifold pressure signal and spring force to detect when the throttle is closed. When the throttle is closed rapidly, the BOV vents boost in the intake tract to atmosphere to relieve the pressure; helping to eliminate the phenomenon of surge.
On the exhaust side, a Wastegates provides us a means to control the boost pressure of the engine. Some commercial diesel applications do not use a Wastegates at all. This type of system is called a free-floating turbocharger.
However, the vast majority of gasoline performance applications require a Wastegates. There are two (2) configurations of Wastegates, internal or external. Both internal and external Wastegates provide a means to bypass exhaust flow from the turbine wheel. Bypassing this energy (e.g. exhaust flow) reduces the power driving the turbine wheel to match the power required for a given boost level. Similar to the BOV, the Wastegates uses boost pressure and spring force to regulate the flow bypassing the turbine.
Internal Wastegates are built into the turbine housing and consist of a “flapper” valve, crank arm, rod end, and pneumatic actuator. It is important to connect this actuator only to boost pressure; i.e. it is not designed to handle vacuum and as such should not be referenced to an intake manifold.
External Wastegates are added to the exhaust plumbing on the exhaust manifold or header. The advantage of external Wastegates is that the bypassed flow can be reintroduced into the exhaust stream further downstream of the turbine. This tends to
improve the turbine’s performance. On racing applications, this Wastegated exhaust flow can be vented directly to atmosphere.
Oil & Water Plumbing
The intake and exhaust plumbing often receives the focus leaving the oil and water plumbing neglected.
Garrett ball bearing turbochargers require less oil than journal bearing turbos. Therefore an oil inlet restrictor is recommended if you have oil pressure over about 60 psig. The oil outlet should be plumbed to the oil pan above the oil level (for wet sump systems). Since the oil drain is gravity fed, it is important that the oil outlet points downward, and that the drain tube does not become horizontal or go “uphill” at any point.
Following a hot shutdown of a turbocharger, heat soak begins. This means that the heat in the head, exhaust manifold, and turbine housing finds it way to the turbo’s center housing, raising its temperature. These extreme temperatures in the center housing can result in oil coking.
To minimize the effects of heat soak-back, water-cooled center housings were introduced. These use coolant from the engine to act as a heat sink after engine shutdown, preventing the oil from coking. The water lines utilize a thermal siphon effect to reduce the peak heat soak-back temperature after key-off. The layout of the pipes should minimize peaks and troughs with the (cool) water inlet on the low side. To help this along, it is advantageous to tilt the turbocharger about 25° about the axis of shaft rotation.
Many Garrett turbos are water-cooled for enhanced durability.
Which Turbocharger is Right for Me or more affectionately known as My Turbo & Me
Selecting the proper turbocharger for your specific application requires many inputs. With decades of collective turbocharging experience, the Garrett Performance Distributors can assist in selecting the right turbocharger for your application.
The primary input in determining which turbocharger is appropriate is to have a target horsepower in mind. This should be as realistic as possible for the application. Remember that engine power is generally proportional to air and fuel flow. Thus, once you have a target power level identified, you begin to hone in on the turbocharger size, which is highly dependent on airflow requirements.
Other important factors include the type of application. An autocross car, for example, requires rapid boost response. A smaller turbocharger or smaller turbine housing would be most suitable for this application. While this will trade off ultimate power due to increased exhaust backpressure at higher engine speeds, boost response of the small turbo will be excellent.
Alternatively, on a car dedicated to track days, peak horsepower is a higher priority than low-end torque. Plus, engine speeds tend to be consistently higher. Here, a larger turbocharger or turbine housing will provide reduced backpressure but less-immediate low-end response. This is a welcome tradeoff given the intended operating conditions.
Selecting the turbocharger for your application goes beyond “how much boost” you want to run. Defining your target power level and the primary use for the application are the first steps in enabling your Garrett Performance Distributor to select the right turbocharger for you.
Journal Bearings vs. Ball Bearings
The journal bearing has long been the brawn of the turbocharger, however a ball-bearing cartridge is now an affordable technology advancement that provides significant performance improvements to the turbocharger.
Ball bearing innovation began as a result of work with the Garrett Motorsports group for several racing series where it received the term the ‘cartridge ball bearing’. The cartridge is a single sleeve system that contains a set of angular contact ball bearings on either end, whereas the traditional bearing system contains a set of journal bearings and a thrust bearing
Turbo Response – When driving a vehicle with the cartridge ball bearing turbocharger, you will find exceptionally crisp and strong throttle response. Garrett Ball Bearing turbochargers spool up 15% faster than traditional journal bearings. This produces an improved response that can be converted to quicker 0-60 mph speed. In fact, some professional drivers of Garrett ball-bearing turbocharged engines report that they feel like they are driving a big, normally aspirated engine.
Tests run on CART turbos have shown that ball-bearings have up to half of the power consumption of traditional bearings. The result is faster time to boost which translates into better drivability and acceleration.
On-engine performance is also better in the steady-state for the Garrett Cartridge Ball Bearing
Reduced Oil Flow – The ball bearing design reduces the required amount of oil required to provide adequate lubrication. This lower oil volume reduces the chance for seal leakage. Also, the ball bearing is more tolerant of marginal lube conditions, and diminishes the possibility of turbocharger failure on engine shut down.
Improved Rotordynamics and Durability – The ball bearing cartridge gives better damping and control over shaft motion, allowing enhanced reliability for both everyday and extreme driving conditions. In addition, the opposed angular contact bearing cartridge eliminates the need for the thrust bearing commonly a weak link in the turbo bearing system.
Competitor Ball Bearing Options – Another option one will find is a hybrid ball bearing. This consists of replacing only the compressor side journal bearing with a single angular contact ball bearing. Since the single bearing can only take thrust in one direction, a thrust bearing is still necessary and drag in the turbine side journal bearing is unchanged. With the Garrett ball bearing cartridge the rotor-group is entirely supported by the ball bearings, maximizing efficiency, performance, and durability.
Ball Bearings in Original Equipment – Pumping up the MAZDASPEED Protegé’s heart rate is a Garrett T25 turbocharger system. With Garrett technology on board, the vehicle gains increased acceleration without sacrificing overall efficiency and it has received many rave reviews from the world’s top automotive press for it’s unprecedented performance.
Source by Honeywell Garrett
And here’s its Wiki site for Turbochargers:
Turbocharger - Wikipedia, the free encyclopedia
Getting more fuel into the charge would make for a more powerful explosion. But you can't simply pump more fuel into the engine because an exact amount of oxygen is required to burn a given amount of fuel. This chemically correct mixture -- 14 parts air to one part fuel -- is essential for an engine to operate efficiently. The bottom line: To put in more fuel, you have to put in more air.
That's the job of the supercharger. Superchargers increase intake by compressing air above atmospheric pressure, without creating a vacuum. This forces more air into the engine, providing a "boost." With the additional air in the boost, more fuel can be added to the charge, and the power of the engine is increased. Supercharging adds an average of 46 percent more horsepower and 31 percent more torque. In high-altitude situations, where engine performance deteriorates because the air has low density and pressure, a supercharger delivers higher-pressure air to the engine so it can operate optimally.
ProCharger D1SC centrifugal supercharger
To pressurize the air, a supercharger must spin rapidly -- more rapidly than the engine itself. Making the drive gear larger than the compressor gear causes the compressor to spin faster. Superchargers can spin at speeds as high as 50,000 to 65,000 rotations per minute (RPM).
A compressor spinning at 50,000 RPM translates to a boost of about six to nine pounds per square inch (psi). That's six to nine additional psi over the atmospheric pressure at a particular elevation. Atmospheric pressure at sea level is 14.7 psi, so a typical boost from a supercharger places about 50 percent more air into the engine.
As the air is compressed, it gets hotter, which means that it loses its density and can not expand as much during the explosion. This means that it can't create as much power when it's ignited by the spark plug. For a supercharger to work at peak efficiency, the compressed air exiting the discharge unit must be cooled before it enters the intake manifold. The intercooler is responsible for this cooling process. Intercoolers come in two basic designs: air-to-air intercoolers and air-to-water intercoolers. Both work just like a radiator, with cooler air or water sent through a system of pipes or tubes. As the hot air exiting the supercharger encounters the cooler pipes, it also cools down. The reduction in air temperature increases the density of the air, which makes for a denser charge entering the combustion chamber.
Types of Supercharger
There are three types of superchargers: Roots, twin-screw and centrifugal. The main difference is how they move air to the intake manifold of the engine. Roots and twin-screw superchargers use different types of meshing lobes, and a centrifugal supercharger uses an impeller, which draws air in. Although all of these designs provide a boost, they differ considerably in their efficiency. Each type of supercharger is available in different sizes, depending on whether you just want to give your car a boost or compete in a race.
A twin-screw supercharger operates by pulling air through a pair of meshing lobes that resemble a set of worm gears. Like the Roots supercharger, the air inside a twin-screw supercharger is trapped in pockets created by the rotor lobes. But a twin-screw supercharger compresses the air inside the rotor housing. That's because the rotors have a conical taper, which means the air pockets decrease in size as air moves from the fill side to the discharge side. As the air pockets shrink, the air is squeezed into a smaller space.
Twin Screw Supercharger
A centrifugal supercharger powers an impeller -- a device similar to a rotor -- at very high speeds to quickly draw air into a small compressor housing. Impeller speeds can reach 50,000 to 60,000 RPM. As the air is drawn in at the hub of the impeller, centrifugal force causes it to radiate outward. The air leaves the impeller at high speed, but low pressure. A diffuser -- a set of stationary vanes that surround the impeller -- converts the high-speed, low-pressure air to low-speed, high-pressure air. Air molecules slow down when they hit the vanes, which reduces the velocity of the airflow and increases pressure.
*Information gathered from HowStuffWorks.com
And here’s the Wiki site for Superchargers:
Supercharger - Wikipedia, the free encyclopedia
- Feel free to PM me more information or a change of information if you feel the need to do so. Majority of this information was gathered from a previous thread by members on this forum and the rest of the information was gathered from websites.