turbo2.4
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 posted on 3-9-2010 at 04:35 PM |
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James brings you the Turbo knowledge!
I found this on http://www.turbochargerpros.com/about-turbocharger.html
If you are new to turbos or just want to know better how they work,take a look. I will keep bringing articles like these to the site.You never know
what you may learn. If you are already a turbo veteran,feel free to add your knowledge and experience.
Remember,we all had to start learning somewhere.
Turbocharger
This article describes the internal combustion engine component often known as a turbo. For other meanings of turbo, see turbo (disambiguation).
Turbocharger cutaway
A turbocharger is an exhaust gas driven compressor used in internal-combustion engines to increase the power output of the engine by increasing the
mass of oxygen entering the engine. A key advantage of turbochargers is that they offer a considerable increase in engine power with only a slight
increase in weight.
Principle of operation
A turbocharger is an exhaust gas driven supercharger. All superchargers have a gas compressor in the intake tract of the engine which compresses the
intake air above atmospheric pressure, greatly increasing the volumetric efficiency beyond that of naturally-aspirated engines. A turbocharger also
has a turbine that powers the compressor using wasted energy from the exhaust gases. The compressor and turbine spin on the same shaft, similar to a
turbojet aircraft engine.
The term supercharger is very often used when referring to a mechanically driven turbocharger, which is most often driven from the engine's
crankshaft by means of a belt (otherwise, and in many aircraft engines, by a geartrain), whereas a turbocharger is exhaust-driven, the name
turbocharger being a contraction of the earlier "turbosupercharger". Because the turbine of a turbocharger is in-itself a heat engine, a
turbocharger equipped engine will normally compress the intake air more efficiently than a mechanical supercharger. But because of "turbo lag" (see
below), engines with mechanical superchargers are typically more responsive.
The compressor increases the pressure of the air entering the engine, so a greater mass of oxygen enters the combustion chamber in the same time
interval (an increase in fuel is required to keep the mixture the same air to fuel ratio). This greatly improves the volumetric efficiency of the
engine, and thereby creates more power. The additional fuel is provided by the proper tuning of the fuel injectors or carburetor.
The increase in pressure is called "boost" and is measured in pascals, bars or lbf/in². The energy from the extra fuel leads to more overall engine
power. For example, at 100% efficiency a turbocharger providing 101 kPa (14.7 lbf/in²) of boost would effectively double the amount of air entering
the engine because the total pressure is twice atmospheric pressure. However, there are some parasitic losses due to heat and exhaust backpressure
from the turbine, so turbochargers are generally only about 80% efficient, at peak efficiency, because it takes some work for the engine to push those
gases through the turbocharger turbine (which is acting as a restriction in the exhaust) and the now-compressed intake air has been heated, reducing
its density.
For automobile use, typical boost pressure is in the general area of 80 kPa (11.6 lbf/in²), but it can be much more. Because it is a centrifugal pump,
a typical turbocharger, depending on design, will only start to deliver boost from a certain rpm where the engine starts producing enough exhaust gas
to spin the turbocharger fast enough to make pressure. This engine rpm is referred to as the boost threshold. Another fact to observe is that the
relation between boost pressure and compressor rpm is somewhat exponential, and the relation between compressor rpm and airflow is very small. A
turbocharger that is pushing 15 psi when the engine is at 3000 rpm will only have increased a little bit in speed when maintaining the same pressure
at 6000 engine rpm; given that it is still within the design limits of the compressor. For this very same reason, belt driven centrifugal
superchargers have a very narrow power band and deliver max boost only when the engine is at max rpm.
A disadvantage in gasoline engines is that the compression ratio should be lowered (so as not to exceed maximum compression pressure and to prevent
engine knocking) which reduces engine efficiency when operating at low power. This disadvantage does not apply to specifically designed turbocharged
diesel engines. However, for operation at altitude, the power recovery of a turbocharger makes a big difference to total power output of both engine
types. This last factor makes turbocharging aircraft engines considerably advantageous—and was the original reason for development of the device.
A main disadvantage of high boost pressures for internal combustion engines is that compressing the inlet air increases its temperature. This increase
in charge temperature is a limiting factor for petrol engines that can only tolerate a limited increase in charge temperature before detonation
occurs. The higher temperature is a volumetric efficiency downgrade for both types of engine. The pumping-effect heating can be alleviated by
aftercooling (sometimes called intercooling).
A Pair of turbochargers mounted to an Inline 6 engine in a dragster.
Design details
When a gas is compressed, its temperature rises. It is not uncommon for a turbocharger to be pushing out air that is 90 °C (200°F). Compressed air
from a turbo may be (and most commonly is, on petrol engines) cooled before it is fed into the cylinders, using an intercooler or a charge air cooler
(a heat-exchange device).
A turbo spins very fast; most peak between 80,000 and 150,000 rpm (using low inertia turbos, 190,000 rpm) depending on size, weight of the rotating
parts, boost pressure developed and compressor design. Such high rotation speeds would cause problems for standard ball bearings leading to failure so
most turbo-chargers use fluid bearings. These feature a flowing layer of oil that suspends and cools the moving parts. The oil is usually taken from
the engine-oil circuit and usually needs to be cooled by an oil cooler before it circulates through the engine. Some turbochargers use incredibly
precise ball bearings that offer less friction than a fluid bearing but these are also suspended in fluid-dampened cavities. Lower friction means the
turbo shaft can be made of lighter materials, reducing so-called turbo lag or boost lag. Some car makers use water cooled turbochargers for added
bearing life.
Turbochargers with foil bearings are in development which eliminates the need for bearing cooling or oil delivery systems.
To manage the upper-deck air pressure, the turbocharger's exhaust gas flow is regulated with a wastegate that bypasses excess exhaust gas entering
the turbocharger's turbine. This regulates the rotational speed of the turbine and the output of the compressor. The wastegate is opened and closed
by the compressed air from turbo (the upper-deck pressure) and can be raised by using a solenoid to regulate the pressure fed to the wastegate
membrane. This solenoid can be controlled by Automatic Performance Control, the engine's electronic control unit or an after market boost control
computer. Another method of raising the boost pressure is through the use of check and bleed valves to keep the pressure at the membrane lower than
the pressure within the system.
Some turbochargers utilise a set of vanes in the exhaust housing to maintain a constant gas velocity across the turbine, the same kind of control as
used on power plant turbines. These turbochargers have minimal amount of lag, have a low boost threshold, and are very efficient at higher engine
speeds. In many setups these turbos don't even need a wastegate. The vanes are controlled by a membrane identical to the one on a wastegate but the
level of control required is a bit different. The first car manufacturer to use these turbos was the limited-production 1989 Shelby CSX-VNT. It
utilised a turbo from Garrett, called the VNT-25 because it uses the same compressor and shaft as the more common Garrett T-25. This type of turbine
is called a Variable Nozzle Turbine (VNT). Turbocharger manufacturer Aerocharger uses the term 'Variable Area Turbine Nozzle' (VATN) to describe
this type of turbine nozzle. Another common term is Variable Turbine Geometry.
Reliability
As long as the oil supply is clean and the exhaust gas does not become overheated (lean mixtures or retarded spark timing on a gasoline engine) a
turbocharger can be very reliable but care of the unit is important. Replacing a turbo that lets go and sheds its blades will be expensive. The use of
synthetic oils is recommended in turbo engines.
After high speed operation of the engine it is important to let the engine run at idle speed for one to three minutes before turning off the engine.
Saab, in its owner manuals, recommends a period of just 30 seconds. This lets the turbo rotating assembly cool from the lower exhaust gas
temperatures. Not doing this will also result in the critical oil supply to the turbocharger being severed when the engine stops while the turbine
housing and exhaust manifold are still very hot, leading to coking (burning) of the lubricating oil trapped in the unit when the heat soaks into the
bearings and later, failure of the supply of oil when the engine is next started causing rapid bearing wear and failure. Even small particles of burnt
oil will accumulate and lead to choking the oil supply and failure. A turbo timer is a device designed to keep an automotive engine running for a
pre-specified period of time, in order to execute this cool-down period automatically.
Turbos with watercooled bearing cartridges have a protective barrier against coking. The water boils in the cartridge when the engine is shut off and
forms a natural recirculation to drain away the heat. It is still a good idea to not shut the engine off while the turbo and manifold are still
glowing.
In custom applications utilising tubular headers rather than cast iron manifolds, the need for a cooldown period is reduced because the lighter
headers store much less heat than heavy cast iron manifolds.
Diesel engines are usually much kinder to turbos because their exhaust gas temperature is much lower than that of gasoline engines and because most
operators allow the engine to idle and do not switch it off immediately after heavy use.
Lag
A lag is sometimes felt by the driver of a turbocharged vehicle as a delay between pushing on the accelerator pedal and feeling the turbo kick-in.
This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its
rotational inertia and reach the speed necessary to supply boost pressure. The directly-driven compressor in a positive-displacement supercharger does
not suffer this problem. (Centrifugal superchargers do not build boost at low RPM's like a positive displacement supercharger will). Conversely on
light loads or at low rpm a turbocharger supplies less boost and the engine is more efficient than a supercharged engine.
Lag can be reduced by lowering the rotational inertia of the turbine, for example by using lighter parts to allow the spool-up to happen more quickly.
Ceramic turbines are a big help in this direction. Unfortunately, their relative fragility limits the maximum boost they can supply. Another way to
reduce lag is to change the aspect ratio of the turbine by reducing the diameter and increasing the gas-flow path-length. Increasing the upper-deck
air pressure and improving the wastegate response help but there are cost increases and reliability disadvantages that car manufacturers are not happy
about. Lag is also reduced by using a precision bearing rather than a fluid bearing, this reduces friction rather than rotational inertia but
contributes to faster acceleration of the turbo's rotating assembly.
Another common method of equalizing turbo lag, is to have the turbine wheel "clipped", or to reduce the surface area of the turbine wheel's
rotating blades. By clipping a minute portion off the tip of each blade of the turbine wheel, less restriction is imposed upon the escaping exhaust
gases. This imparts less impedance onto the flow of exhaust gasses at low rpm, allowing the vehicle to retain more of its low-end torque, but also
pushes the effective boost rpm to a slightly higher level. The amount a turbine wheel is and can be clipped is highly application-specific. Turbine
clipping is measured and specified in degrees.
Other setups, most notably in V-type engines, utilize two identically-sized but smaller turbos, each fed by a separate set of exhaust streams from the
engine. The two smaller turbos produce the same (or more) aggregate amount of boost as a larger single turbo, but since they are smaller they reach
their optimal rpm, and thus optimal boost delivery, faster. Such an arrangement of turbos is typically referred to as a "twin turbo" setup.
Some car makers combat lag by using two small turbos (like Toyota, Subaru, Maserati, Mazda, and Audi). A typical arrangement for this is to have one
turbo active across the entire rev range of the engine and one coming on-line at higher rpm. Early designs would have one turbocharger active up to a
certain rpm, after which both turbochargers are active. Below this rpm, both exhaust and air inlet of the secondary turbo are closed . Being
individually smaller they do not suffer from excessive lag and having the second turbo operating at a higher rpm range allows it to get to full
rotational speed before it is required. Such combinations are referred to as "sequential turbos". Sequential turbochargers are usually much more
complicated than single or twin-turbocharger systems because they require what amounts to three sets of pipes-intake and wastegate pipes for the two
turbochargers as well as valves to control the direction of the exhaust gases. An example of this is the current BMW E60 5-Series 535d. Many new
diesel engines use this technology to not only eliminate lag but also to reduce fuel consumption and produce cleaner emissions. An example of this
would be the Ford Power Stroke engine.
Lag is not to be confused with the boost threshold, however many publications still make this basic mistake. The boost threshold of a turbo system
describes the minimum turbo rpm at which the turbo is physically able to supply the requested boost level. Newer turbocharger and engine developments
have caused boost thresholds to steadily decline to where day-to-day use feels perfectly natural. Putting your foot down at 1200 engine rpm and having
no boost until 2000 engine rpm is an example of boost threshold and not lag.
Race cars often utilise anti-lag to completely eliminate lag at the cost of reduced turbocharger life.
On modern diesel engines, this problem is virtually eliminated by utilising a variable geometry turbocharger. The newly presented Porsche 911 Turbo
has eliminated this problem for gasoline engines as well.
Boost
Boost refers to the increased manifold pressure that is generated by the intake side turbine. This is limited to keep the turbo inside its design
operating range by controlling the wastegate which shunts the exhaust gases away from the exhaust side turbine. Many diesel engines do not have any
wastegate because the amount of exhaust energy is controlled directly by the amount of fuel injected into the engine, and slight variations in boost
pressure do not make a difference for the engine.
Applications
Turbocharging is very common on diesel engines in conventional automobiles, in trucks, for marine and heavy machinery applications. In fact, for
current automotive applications, non-turbocharged diesel engines are becoming increasingly rare. Diesels are particularly suitable for turbocharging
for several reasons:
· Naturally-aspirated diesels have lower power-to-weight ratios compared to gasoline engines; turbocharging will improve this P:W ratio.
· Diesel engines require more robust construction because they already run at very high compression ratio and at high temperatures so they
generally require little additional reinforcement to be able to cope with the addition of the turbocharger. Gasoline engines often require extensive
modification for turbocharging.
· Diesel engines have a narrower band of engine speeds at which they operate, thus making the operating characteristics of the turbocharger
over that "rev range" less of a compromise than on a gasoline-powered engine.
· Diesel engines blow nothing but air into the cylinders during cylinder charging, squirting fuel into the cylinder only after the intake
valve has closed and compression has begun. Gasoline/petrol engines differ from this in that both fuel and air are introduced during the intake cycle
and both are compressed during the compression cycle. The higher intake charge temperatures of forced-induction engines reduces the amount of
compression that is possible with a gasoline/petrol engine, whereas diesel engines are far less sensitive to this.
Today, turbocharging is most commonly used on two types of engines: Gasoline engines in high-performance automobiles and diesel engines in work
trucks. Small cars in particular benefit from this technology, as there is often little room to fit a larger-output (and physically larger) engine.
Saab has been the leading car maker using turbochargers in production cars, starting with the 1978 Saab 99. The Porsche 944 utilized a turbo unit in
the 944 Turbo (Porsche internal model number 951), to great advantage, bringing its 0-100 km/h (0-60 mph) times very close to its contemporary
non-turbo "big brother", the Porsche 928. Contemporary examples of turbocharged performance cars include the Audi TT, Dodge SRT-4, Subaru Impreza
WRX, Mazda RX-7, Mitsubishi Lancer Evolution, Nissan Skyline GT-R, Toyota Supra RZ, and the Porsche 911 Turbo.
Small car turbos are increasingly being used as the basis for small jet engines used for flying model aircraft—though the conversion is a highly
specialised job—one not without its dangers.
Most modern turbocharged aircraft use an adjustable wastegate. The wastegate is controlled manually, or by a pneumatic/hydraulic control system, or,
as is becoming more and more common, by a flight computer. In the interests of engine longevity, the wastegate is usually kept open, or nearly so, at
sea-level to keep from overboosting the engine. As the aircraft climbs, the wastegate is gradually closed, maintaining the manifold pressure at or
above sea-level. In aftermarket applications, aircraft turbochargers sometimes do not overboost the engine, but rather compress ambient air to
sea-level pressure. For this reason, such aircraft are sometimes refered to as being turbo-normalised. Most applications produced by the major
manufacturers (Beech, Cessna, Piper and others) increase the maximum engine intake air pressure by as much as 35%. Special attention to engine cooling
and component strength is required because of the increased combustion heat and power.
Turbo-Alternator[1] is a form of turbocharger that generates electricity instead of boosting engine's air flow. On September 21, 2005, Foresight
Vehicle announced the first known implementation of such unit for automobiles, under the name TIGERS (Turbo-generator Integrated Gas Energy Recovery
System).[2]
History
The turbocharger was invented by Swiss engineer, Alfred Buchi, who had been working on steam turbines. His patent for the internal combustion
turbocharger was applied for in 1905. Diesel ships and locomotives with turbochargers began appearing in the 1920s.
One of the first applications of a turbocharger to a non-Diesel engine came when General Electric engineer, Sanford Moss attached a turbo to a V12
Liberty aircraft engine. The engine was tested at Pike's Peak in Colorado at 14,000 feet to demonstrate that it could eliminate the power losses
usually experienced in internal combustion engines as a result of altitude.
Turbochargers were first used in production aircraft engines in the 1930s prior to World War II. The primary purpose behind most aircraft-based
applications was to increase the altitude at which the airplane can fly, by compensating for the lower atmospheric pressure present at high altitude.
Aircraft such as the Lockheed P-38 Lightning, Boeing B-17 Flying Fortress and B-29 Superfortress all used exhaust driven "turbo-superchargers" to
increase high altitude engine power. It is important to note that turbosupercharged aircraft engines actually utilized a gear-driven centrifugal type
supercharger in series with a turbocharger.
Turbo-Diesel trucks were produced in Europe and America (notably by Cummins) after 1949. The turbocharger hit the automobile world in 1952 when Fred
Agabashian qualified for pole position at the Indianapolis 500 and led for 100 miles before tire shards disabled the blower.
The first production turbocharged automobile engines came from General Motors. The A-body Oldsmobile Cutlass Jetfire and Chevrolet Corvair Monza
Spyder were both fitted with turbochargers in 1962. The Oldsmobile is often recognized as the first, since it came out a few months earlier than the
Corvair. Its Turbo Jetfire was a 215 in³ (3.5 L) V8, while the Corvair engine was either a 145 in³ (2.3 L)(1962-63) or a 164 in³ (2.7 L) (1964-66)
flat-6. Both of these engines were abandoned within a few years, and GM's next turbo engine came more than two decades later.
Offenhauser's turbocharged engines returned to Indianapolis in 1966, with victories coming in 1968. The Offy turbo peaked at over 1,000 hp in 1973,
while Porsche dominated the Can-Am series with a 1100 hp 917/30. Turbocharged cars dominated the Le Mans between 1976 and 1994.
BMW led the resurgence of the automobile turbo with the 1973 2002 Turbo, with Porsche following with the 911 Turbo, introduced at the 1974 Paris Motor
Show. Buick was the first GM division to bring back the turbo, in the 1978 Buick Regal, followed by the famed Mercedes-Benz 300D and Saab 99 in 1978.
The worlds first production turbodiesel automobile was also introduced in 1978 by Peugeot with the launch of the Peugeot 604 turbodiesel. Pontiac also
introduced a turbo in 1980 and Volvo Cars followed in 1981
In Formula 1, in the so called "Turbo Era" of 1977 until 1989, engines with a capacity of 1500 cc could achieve anywhere from 1000 to 1500 hp (746
to 1119 kW) (Renault, Honda, BMW). Renault was the first manufacturer to apply turbo technology in the F1 field, in 1977. The project's high cost was
compensated for by its performance, and led to other engine manufacturers following suit. The Turbo-charged engines took over the F1 field and ended
the Ford Cosworth DFV era in the mid 1980s.
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2DRSRT4
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Posts: 2775
Registered: 1-22-2010
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![[*]](./images/xn/default_icon.gif) posted on 3-9-2010 at 05:02 PM |
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Nice write up James. It's quite detailed.
97 neon
All stock.. For now......
69 C10
L6 6 cylinder engine, hoping to swap out for a 454 soon enough. Stock 3 speed on the floor with a Hurst Indy shifter.
65 C20
283 small block, 4 speed on the floor with granny gear in first. (FOR SALE!!!)
Friends don't let friends drive FORDS!! LOL
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turbo2.4
Super Moderator
Posts: 2110
Registered: 12-5-2009
Location: Stuck in the tailcone of a Blackhawk,Texas
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Mood: Sheetmetal Samurai
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| posted on 3-10-2010 at 02:09 PM |
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I am actually surprised that they did not go any farther than that on the F1 applications and how the turbos became so regulated that they became
obsolete.
A book that is worth looking into is called 'Maximum Boost' by corky bell. That was at one time considered the boosting bible. I never spent the
money on it, but I have read it in increments at the book store. Ha ha
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2DRSRT4
Posting Freak
Posts: 2775
Registered: 1-22-2010
Location: El Paso, TX
Member Is Online
Mood: Eh..
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| posted on 3-10-2010 at 06:30 PM |
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Haha nice one. I might try to find it at Barnes over here
97 neon
All stock.. For now......
69 C10
L6 6 cylinder engine, hoping to swap out for a 454 soon enough. Stock 3 speed on the floor with a Hurst Indy shifter.
65 C20
283 small block, 4 speed on the floor with granny gear in first. (FOR SALE!!!)
Friends don't let friends drive FORDS!! LOL
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turbo2.4
Super Moderator
Posts: 2110
Registered: 12-5-2009
Location: Stuck in the tailcone of a Blackhawk,Texas
Member Is Online
Mood: Sheetmetal Samurai
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| posted on 3-11-2010 at 02:59 PM |
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Last I checked the book still goes for about $40 but I dare say it would be money well spent.
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2DRSRT4
Posting Freak
Posts: 2775
Registered: 1-22-2010
Location: El Paso, TX
Member Is Online
Mood: Eh..
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| posted on 3-16-2010 at 05:27 PM |
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Alright, sounds pricey but oh well. Worth it indeed.
97 neon
All stock.. For now......
69 C10
L6 6 cylinder engine, hoping to swap out for a 454 soon enough. Stock 3 speed on the floor with a Hurst Indy shifter.
65 C20
283 small block, 4 speed on the floor with granny gear in first. (FOR SALE!!!)
Friends don't let friends drive FORDS!! LOL
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turbo2.4
Super Moderator
Posts: 2110
Registered: 12-5-2009
Location: Stuck in the tailcone of a Blackhawk,Texas
Member Is Online
Mood: Sheetmetal Samurai
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| posted on 4-12-2010 at 03:01 PM |
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WORK IN PROGRESS
Turbo Tech - Turbos!
HOT ROD's guide to the ultimate power-adder
From the February, 2009 issue of Hot Rod
Photography by Marlan Davis
Part I: Science & Selection
We've all heard the homilies, "There's no replacement for displacement," and "You just can't beat cubic inches." The basis for these statements
is that the greater an engine's displacement, the more air and fuel can be squeezed into the cylinders, and the higher its potential power output.
But they're not entirely accurate: There is another way to stuff more air and fuel into the cylinders--lots more, in fact--without increasing an
engine's size. It's called supercharging, which is a way to force more air into an engine than it could normally take in by atmospheric pressure
alone. Only the most efficient normally aspirated race engines with very specialized induction tuning can exceed 100 percent volumetric efficiency
(VE), but a supercharger's forced induction makes exceeding 100 percent easy; 15 pounds of boost pressure (defined as pressure above the normal 14.7
psi atmospheric pressure) effectively doubles an engine's displacement--with correspondingly huge potential horsepower increases.
Turbos have three major subassemblies:... read full captionTurbos have three major subassemblies: an exhaust turbine housing, a bearing housing,
and a compressor housing. The exhaust and bearing housings each have a wheel with integral blades, and are connected together by a shaft mounted on
bearings. Some turbos--like this Turbonetics Super Thumper that can support over 2,400 hp--offer a ceramic ball bearing option. A: Turbine wheel, B:
Bearing and seal, C: Turbo shaft, D: Exhaust turbine housing, E: Backplate, F: Compressor wheel, G: Compressor housing, H: Bearing housing, I: Inducer
bore, J: Exducer bore"Supercharger" is a generic term for any forced-induction compressor that is driven by a belt, gears, or a turbine. The
turbine-driven version is known as a turbocharger, and it has the potential to be the most efficient power-adder for an internal-combustion engine on
the planet. An internal-combustion engine is notoriously inefficient: Only about one-third of the energy released during combustion actually drives
the crank. Of the remaining two-thirds, one-third goes into the cooling system, and one-third goes out the exhaust as heat. In fact, a 200hp engine
dumps the equivalent of about 70 hp of raw heat straight out the tailpipe! However, a turbo's turbine-wheel is driven by the engine's own exhaust
gases as they exit the motor, so some of the heat that normally goes to waste is now used to power a compressor that pumps more air into the
engine.
Although a turbo's position in the exhaust stream does restrict exhaust flow potential to some extent, the pumping losses are much less than the
parasitic drag induced by a conventional supercharger's belt or gears. In a typical gasoline-fueled engine, it's common to see 30 out of every 100
hp added by a beltdriven supercharger being wasted turning the drive pulleys and belts; this compares to about 5-10 hp per every 100 suffered as
pumping losses by a typical well-designed turbo installation. Considered as a system, the turbo setup has less heat buildup than an old-style Roots
blower, and its smaller size compared to a centrifugal supercharger permits higher compressor-wheel rotational speeds and more radical blade-tip
curvature that collectively translate into greater pumping efficiency.
The little brother of the... read full captionThe little brother of the TO4 (far right) is the T3 (far left). The T3's envelope is about 25
percent smaller, making it easier to package. Turbonetics says many street V-8s run OK with T3 or T3/TO4 hybrids, which is a real godsend in a tight
engine compartment.If turbos are so cool, why don't we see more of them on street machines outside of imports? In racing, it's discrimination, plain
and simple. Turbos are dominant anywhere they're allowed to compete against beltdriven blowers (as well as nitrous oxide), so rule-makers almost
always legislate against them, adding weight, reducing displacement, or relegating them to a separate class. On the street, it's due to perceived
complexity and installation difficulty. While these issues certainly aren't trifles, in these pages--with help from Innovative Turbo, Turbonetics,
and other turbo specialists--HOT ROD will attempt to demystify some of these complexities and get you started on the road to making some serious
horsepressure.
The Feedback Loop
There are four TO4 turbine... read full captionThere are four TO4 turbine wheel trims (rear row)--N, O, P, and Q. The large Q-trim reduces
backpressure, but being heavier, it spools up slower. Each trim level is available in two shaft diameters and with a choice of ball or plain bearings.
In the front and middle rows are just 10 of the literally dozens of TO4 compressor wheel trims; they're ID'ed by numbers.There are a bewildering
variety of turbo configurations, but they're all similar in appearance and function: During engine operation, hot exhaust gases blow out of the
engine's exhaust ports, into the exhaust manifold, through connecting tubing, and into the turbo's turbine housing. They strike the blades on the
turbine wheel and make it spin. When the turbine wheel spins, so does the compressor wheel. As the compressor wheel rotates, it sucks air (or both air
and fuel in the case of a draw-through carbureted setup) into the compressor housing. Centrifugal force throws the air outward, causing it to flow out
of the turbo into the intake manifold under pressure.
As engine speed and boost increase, the turbo becomes self-feeding: The more air the compressor packs into the engine, the more exhaust gas is
generated, which causes the turbine wheel to spin faster, in turn spinning the compressor faster and packing more air into the engine.
Turbo bearings are subject... read full captionTurbo bearings are subject to tremendous heat. The water-cooled housing (above left) is
recommended for prolonged highway use. Short-duration competition engines often use an air-cooled housing (above right) for less complexity.The key is
getting the wheels spinning fast enough in the first place to start generating boost and a feedback loop. Turbos are load-sensitive and need energy to
work. If the compressor and turbine wheels are not spinning fast enough when the accelerator pedal is mashed, there will be a slight delay before the
turbo develops sufficient boost, a phenomenon known as turbo lag. Factors contributing to turbo lag include improper turbocharger selection, the
turbo's physical location within the system, and the inherent limitations of nonelectronically managed engine packages.
No Junkyard Dogs
The most critical aspect of a successful turbocharger installation is the proper selection of the basic turbocharger unit itself. Conventional
superchargers come in only a few different size variations, and their output is easily adjustable by changing the drive-pulley ratio. Turbochargers
come in an enormous array of sizes and shapes to confuse you, and if you select the wrong one, the engine won't function at anywhere near its
potential.
This 358ci small-block Chevy... read full captionThis 358ci small-block Chevy is about as rad as it can get and still use conventional
23-degree-valve-angle heads. Electronically managed by ACCEL Gen 7 DFI, the 10.0:1 engine runs a single large-frame Innovative GTB88 turbo and makes
over 1,400 hp on C-16 race gas. Big race turbos are typically identified by the inducer orifice size--in this case 88 mm.First, you can't just go
down to the salvage yard, pick up an OEM unit, and bolt it onto your hot rod. Its size and design characteristics almost certainly won't be right for
your custom engine from a flow and efficiency standpoint. Its physical layout may also be hard to adapt: The wastegate may be integral with the turbo,
making it hard to mate with other engines' exhaust systems, and the compressor and turbine halves may not be clockable as is the case with
high-performance aftermarket units intended for use on custom installations.
Specifically intended for custom installations, aftermarket units like AirResearch's popular TO4 series are modular and assemble like an erector set,
allowing for variable combinations of turbine housings, compressor housings, turbine wheels, and compressor wheels within a given turbo series. Just
like cams, there are so many factors governing turbo selection that consulting an expert is highly recommended. However, the following overview will
get you close.
Turbo Tech - Turbos!
This graph can be used to... read full captionThis graph can be used to determine engine airflow requirements for 10- and 15-psi boost
levels.Compressor Housing
Turbo size selection begins with choosing the compressor housing (the air-into-engine side of the turbo). Racers operating with high-octane fuel
usually base this on how much horsepower is required to be competitive in their particular racing venue. Street-driven cars operating on available
pump gas are boost-limited, so their primary selection criterion is based on how much turbo their engine combination can accept at a specified boost
level. Generally, 10 psi without an intercooler, or 15 psi with an intercooler (on a well-tuned, electronically managed 8.0:1-compression engine) is
about the best a street guy can hope for on pump gas.
Modern CNC-machining has made... read full captionModern CNC-machining has made it easier to produce trick blade angles that further enhance
performance. Compressor wheels may have radial or backswept blades. Radials yield a faster pressure rise, but are less efficient. Like a loose auto
trans torque converter, Innovative's backswept blades slip more before they start to work, but are more efficient upstairs.Whether you're seeking to
reach a desired power level (for racing) or a specific boost level (on the street), first determine how much airflow is needed to reach your goal at a
given engine displacement and engine rpm. A normally aspirated four-stroke engine's cfm requirements are expressed by the classic formula: VE is at
least 100 percent for a turbocharged engine, so use 1.0 for VE.
Next, you need to add boost into the equation. Turbo engineers use pressure ratio (the ratio of the total absolute pressure produced at the turbo
outlet divided by atmospheric pressure) instead of an outright expression of boost pressure. Compressor pressure ratios corresponding to boost levels
of 10 psi and 15 psi are 1.68 and 2.02, respectively; to find other pressure ratios:
Therefore, the cfm requirement under boost would be:
Cfm boosted = Cfm unboosted x pressure ratio
In the turbo world, engine airflow is measured in pounds/minute (lb/min). To convert cfm to lb/min, a good rule of thumb for 80 degrees F at sea level
is to multiply cfm by 0.07:
Lb/min = cfm boosted x 0.07
Or, use the accompanying graph (above) to determine engine airflow requirements for 10- and 15-psi boost levels.
For any turbo series, the... read full captionFor any turbo series, the higher the A/R ratio, the better the top-end performance. The lower the
A/R ratio, the better the low-speed response.Generally on a high-performance EFI engine, every 1 lb/min of airflow is worth about 10 hp, so to find
the required lb/min for a race-only application, start with the horsepower requirement, then divide by 10:
Lb/min = hp / 10
Every compressor has a definite combination of airflow and boost pressure at which it is most efficient. When choosing a compressor, you want to
position the point of maximum efficiency in the most useful part of the engine's operating range. As efficiency drops off, heat transferred to the
air-induction side of the turbo goes up. That's bad for both power and durability.
A tangential turbine housing... read full captionA tangential turbine housing (left) offers about 4 percent higher flow but has less mounting and
packaging flexibility than the on-center housing (right). In the ubiquitous TO4 line, each design is available in a choice of four different trim
levels (which must match the turbine wheel trim), and up to eight A/R ratios.Turbo manufacturers publish compressor maps that establish the peak
efficiencies of every turbo unit and its variations. These maps are an extremely important part of compressor selection because popular turbo series
like the TO4 and its custom aftermarket derivatives have many different available wheel trims--a classification system that defines the relationship
between the compressor's inducer (inlet orifice) and the compressor wheel overall diameter and tip shape. At first glance, these maps resemble a
topographic contour map, and in a sense the map's bands are describing a turbo's output geography, but in terms of boost and airflow instead of
elevation. They may look complex, but don't be put off. The accompanying sidebar shows how to read a compressor map and use it to select a compressor
for some hypothetical engine combos.
Turbine Housing
Because of the turbocharger's modular nature, in many instances it is possible to mix and match different turbine housings (the exhaust side of the
turbo) with a given compressor housing. This permits tailoring the turbo specifically to the individual engine's operating characteristics and the
vehicle's intended usage.
The turbine must make the compressor spin fast enough to produce the required airflow at the specified boost level. A small turbine spins faster than
a larger turbine (which reduces lag), but develops more backpressure (which restricts exhaust flow). The goal is a turbine that spins fast enough to
generate the necessary response and airflow while minimizing backpressure in the exhaust.
The turbine housing A/R (area/radius)... read full captionThe turbine housing A/R (area/radius) ratio is the area (A) of any turbine inlet scroll
cross-section divided by the distance from the center of that cross-section to the center of the turbine shaft (R). For any given turbine housing, A
and R vary in the same proportions, so all As divided by their corresponding Rs yield the same dividend--which is the A/R ratio.The turbine wheel's
overall diameter and the housing exducer bore (the turbine outlet's id) basically determine the turbine's ability to generate the shaft power needed
to drive the compressor at the flow rate required to create a given boost or power level--or simply put, larger turbines make more power than smaller
turbines.
But brute size is not all that matters. The turbine's A/R (area/radius) ratio basically determines where the turbo starts to accelerate. A turbine
housing looks kinda like a big snail shell. Unwrap the shell and it resembles a cone. Cutting off the tip of the cone leaves a hole--the
cross-sectional area of this hole is the A in A/R. The hole size is important since it determines the velocity at which the exhaust gases exit the
turbine scroll and enter the turbine blades. For a given flow rate, the smaller the hole, the higher the velocity--but the greater the restriction to
exhaust-gas flow.
The compressor housing is... read full captionThe compressor housing is a primary factor in determining how much boost (and power) a turbo is
capable of supporting. There are at least nine different housings available for standard shaft-diameter TO4s alone! Here are three of 'em.The R in
A/R is the distance from the center of the cone's cross-section to the center of the turbine shaft. A smaller R imparts a higher rotating speed to
the turbine; a larger R gives the turbine shaft greater torque to drive the compressor wheel (because the lever arm R is longer).
Why is A/R ratio important? Consider two extremes: Bonneville land-speed racing (LSR) versus quarter-mile drag racing. In an LSR application, the
turbo's rate of acceleration is not critical; the setup can be lazy off-the-line, but the overall acceleration rate, once it begins, should be smooth
and linear--this application generally calls for a high A/R ratio. At the drags (and on a street car), you need more aggressive, instant response,
which tends to lean toward a lower A/R ratio.
Unfortunately there is no easy scientific method for selecting the proper A/R ratio. Seat-of-the-pants feel is important: If boost rise is sluggish,
the ratio is too large. In extreme cases, the ratio gets so big the turbo can't turn fast enough to produce the required boost. But if the ratio is
too small, the turbo gets into boost so quickly that the vehicle becomes almost undriveable--and on top, it will feel like a choked-up normally
aspirated engine that's under-carbureted. Also, what equates to a low or high A/R ratio varies by turbine series and engine displacement. Assuming
the ubiquitous TO4-style turbo on a typical 350ci engine, Innovative offers these A/R guidelines as a starting point, based on where you want the
turbo to work best:
Operating Range; A/R Ratio
Low-end; 0.58
Midrange; 0.69-0.81
High-rpm; 0.96
Turbonetics latest Inconel... read full captionTurbonetics latest Inconel Super T turbine wheels (right) feature 10 improved high-efficiency
blades in place of the previous 11-blade design. Super T turbines fill the gap between the TO4 family that tops out about 900 hp and the huge Super
Thumper family that starts working at 1,400 hp. Inconel is good up to 1,700 degrees F. Need more? Special Mar-M 247 exhaust wheels survive at 2,000
degrees.The accompanying Turbonetics table lists its baseline recommendations for a variety of engine displacements.
Given an equivalent turbine trim and A/R ratio, as engine displacement increases, the operating rpm range characteristics of the turbine decrease.
Then there's also the heat the unit will see from the engine and exhaust gases, which change the unit's efficiency curve. Wastegate location and
design also affects the turbine's performance. The interrelationship of all these factors is extremely complex, so there are no simple selection maps
for turbines like those available for compressors. Even for experienced turbo installers, it often boils down to trial-and-error--kind of like trying
several different size carbs on a normally aspirated motor. About the best advice we can give is that once you've settled on the compressor, consult
your favorite turbo dealer for advice on mating it to a turbine housing that's best suited for your application's needs.
Turbo Tech - Turbos!
One Turbo or Two?
For racing only, there are super-large single turbo setups that can support over 1,500 hp, but they don't work well down low. Generally, when not
restricted by sanctioning body rules, the usual crossover point between single and dual installations is in the 900-1,000hp range. Most under-900hp
requirements can be met by one turbo, typically the universal TO4 or a custom derivative based on the TO4 frame. However, some claim that even in the
under-900hp regime, two smaller turbos reduce lag over one big turbo; others counter that basic physical laws postulate that the reduction in inertia
and flow caused by splitting the exhaust energy in half more than outweighs the supposed advantages of lighter, smaller components--or, in English,
one big turbo housing is more efficient than two smaller housings.
But turbos must also be considered as part of the overall induction and exhaust system. There's no doubt that twin turbos have certain advantages on
V-type engine layouts. The cross-tube on single-turbo V-8 installations can lose a lot of heat, and heat energy powers the turbine; two turbos permit
a greater cross-sectional discharge pipe area, and dual wastegates are more efficient.
Ford 302, Actual displacement:... read full captionFord 302, Actual displacement: 301.59 ci, Peak engine speed: 6,000 rpm, Airflow: 1,057.67 cfm
(74.04 lb/min), HP potential: 740 hp, Compressor: GT76, Approx. efficiency: 66%Finally, there is a special type of dual-turbo setup called
compounding, where multiple turbos are mounted in series instead of in parallel, as is normally the case on a multi-turbo setup. Compounding is for
extremely high boost pressures (on the order of 50-100 psi!) and is usually only encountered on tractor pullers, big diesels, and aircraft. With one
turbo alone making 50 psi under extended operation, the high boost causes shaft overspeed and eventual unit failure. With compounding, a larger unit
mounts ahead of a smaller unit. Since it's able to work harder and draw in more air, the larger unit generates an initial 15 psi or so, which the
smaller unit then multiplies by three or four times to generate high boost without overspeed. With the air already condensed, the second, smaller
turbo is not a restriction.
Honda B18, Actual displacement:... read full captionHonda B18, Actual displacement: 1,834 cc (111.95 ci), Peak engine speed: 9,000 rpm, Airflow:
588.88 cfm (41.22 lb/min), HP potential: 412 hp, Compressor: TO4E-50 trim, Approx. efficiency: 72%We've said that heat is good on the turbine side,
but bad on the inlet side. When an engine makes over 10 psi of boost, heat buildup on the inlet side requires cooling the incoming air down using a
charge-air cooler (aka "intercooler"). We'll get into 'coolers, wastegates, system layout (including turbo location), and turbo engine-building
stuff next month. Stay tuned!
Sample Compressor Maps
These Innovative Turbo maps are just a few examples of some of the many available compressor variations. We've selected them because they meet the
needs of common high-performance engine combinations in terms of efficiency and airflow. The selection is based on 15 psi of boost pressure
(approximately a 2.0:1 pressure ratio), the absolute maximum for an electronically managed and efficiently intercooled engine running on pump gas.
Chevy 350 (+0.030), Actual... read full captionChevy 350 (+0.030), Actual displacement: 355.11 ci, Peak engine speed: 6,500 rpm, Airflow:
1,349.15 cfm (94.44 lb/min), HP potential: 944 hp, Compressors: Two GT61 (47.44 lb/min per turbo), Approx. efficiency: 73%To select a compressor by
means of an airflow map, use the engine airflow in lb/min to establish an operating line on the compressor map for the turbo combo in question. Choose
a map so that the intersection point of lines drawn from the desired engine airflow in lb/hr (the green vertical line in these examples) and the boost
pressure-ratio axis (the blue horizontal line in these examples) ideally falls within the 70-75 percent efficiency region. On an intercooled
application, you can scrape by with as low as 60 percent, but higher is better.
If several different maps seemingly meet your efficiency goal, choose one that has the intersection point farthest to the right side of the 70-75
percent island. This results in quicker turbo response. You want to play in right field.
Chevy 454, Actual displacement:... read full captionChevy 454, Actual displacement: 453.96 ci, Peak engine speed: 6,000 rpm, Airflow: 1,592.01
(111.44 lb/min), HP potential: 1,114 hp, Compressors: Two GT70 (55.75 lb/min per turbo), Approx. efficiency: 70%In a dual turbo installation, divide
the total airflow requirement in half, then select a map that satisfies those conditions. Note that as engine displacement increases, a given turbo
still passes the same amount of air, but observed gauge boost pressure will be lower.
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2DRSRT4
Posting Freak
Posts: 2775
Registered: 1-22-2010
Location: El Paso, TX
Member Is Online
Mood: Eh..
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| posted on 4-12-2010 at 04:00 PM |
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More info. I'm going to do a complete write up when I swap my 2.4 with the turbo. It's good
97 neon
All stock.. For now......
69 C10
L6 6 cylinder engine, hoping to swap out for a 454 soon enough. Stock 3 speed on the floor with a Hurst Indy shifter.
65 C20
283 small block, 4 speed on the floor with granny gear in first. (FOR SALE!!!)
Friends don't let friends drive FORDS!! LOL
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turbo2.4
Super Moderator
Posts: 2110
Registered: 12-5-2009
Location: Stuck in the tailcone of a Blackhawk,Texas
Member Is Online
Mood: Sheetmetal Samurai
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| posted on 5-15-2010 at 06:36 PM |
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Donovan's Dodge garage
http://www.thedodgegarage.com/index.html
Turbo goodness and turbo Mopar history. I think we could all learn from some of the info that is here. Want to see how to run a turbo without
Megasquirt? Know what a cold start injector is? How about a MAP bleed?
Take a look.
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