A lil Turbo Writeup

[Brad98_teg]

Well i got a bit bored and hopefully this will answer some Questions you may have, so here goes...

Supercharging is a way to force more air into an engine that it cuold normally take in by atmospheric pressure alone. Only the most efficient normally aspirated race engines with very specialized induction tuning can exceed 100% volumetric efficiency, but a supercharger's forced induction makes exceeding 100% very easy; 15lbs. of boost pressure effectivly doubles an engines displacement, with correspondingly huge horsepower increases. Turbocharging has the potentail to be the most efficient power-adder for an internal combustion engine on the planet. An internal combustion engine is notoriously inefficint: Only about 1/3 of the energy released during combustion actually drives the crank. Of the remaining 2/3s, 1/3 goes into the cooling system, and the other 1/3 goes strait out your exhaust as heat. A turbo's turbine wheel is driven by the engines 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 turbos position in the exhaust stream does restrict echaust flow potential to some extent, the pumping losses are much less than parasitic drag induced by a conventional supercharger's belt of gears. In a typical gasoline fueled engine, it's common to see 30 out of ever 100hp 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 puming efficiency.

There is a large variety of turbo configurations, but they're all similar in apperiance and function: During engine operation, hot gases blow out of the engine's exhaust ports, into the exhaust manifold, through connecting tubing, and into the tubo's turbine housing. They strike the blades on the turbine wheel and make it spi. When the turbine wheel spins, so does the compressor wheel. As the compressor wheel rotates. it sucks air 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 echaust gas is generated, which causes the turbine wheel to spin faster, in turn spinning the compressor faster and packing more air into the engine. 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 arre not spinning fast enough when the accelerator pedal is mashed, there will be a slight delay before the turbo developes sufficient boost, a phenomenon known as turbo lag is created. Factors contributing to turbo lag include improper tubo charger selection, the turbo's physical location within the system, and the inherent limitations of nonelectronically managed engine packages.

Now the you know some of the basics of a turbocharger, how about looking at parts of the system like the inlet ducting, exhaust piping, wastegates, and others.

Wastegate
Short of buying stock in a piston company,the primary means of preventing engine destroying overboost is an adjustable wastegate. Located in the exhaust collector downstream of any individual primary tubes, a wastegate keeps boost at a preset level by routing excess exhaust gas around the turbine and out the tailpipe or into the atmosphere.

Blow-off Valve
In a blow-through system sudden throttle closure when the engine is under boost can cause the turbo to surge or choke. On a road race,rally, or street car, this can slow response time if you need to quickly get back on the throttle. A blow-off or bypass valve quickly relieves pressre when you back off the throttle. It may be mounted on the compressor out-let duct, between the intercooler and throttlebody, or even directly on the intercooler.

Exhaust Outlet
Also called a downpipe. Smaller outlets help a turbo spool up faster on a street car; larger outlets help flow on the top-end. In any event, the turbine outlet pipe should be no smaller than the exducer size.

Intercooler
Also known as a charge-air cooler, an intercooler is a heat-exchanger that mounts between the turbo and the engine. It draws heat from compressed air exiting the turbo before it reaches the engine. Air-to-Air coolers generally mount in front of the engine-coolant radiator.

Inlet Ducting
Power level defines the inlet duct sizing. Generally the compressor inlet should be about 1 inch larger in outer diameter than the outlet. You can;t go too far wrong if the inlet ducting is the same size as the compressor inducer size.


Well i hope this helps any questions you may have.
Mabey put this in a sticky or make it a sticky to help some people out with some of the basics. :w00t

[mberndt]

Nice writeup...
I'll add a little engineering info...
The ever-lasting post of "what's better: turbo or supercharger" is an interesting topic, because although it is extremely simple in theory, people will continue to argue their side, because they don't understand the operation and the difference between the two...
First, it must be looked at through an engineering standpoint...
Intercoolers are thermodynamic heat exchangers, not fancy articles of style...
They actually DECREASE the amount of work that the engine must produce, (work=power/time) to provide the same level of power without an intercooler.
And work and power are very different values, and have very different units of measurement. (Power=force/time)
Yes, they do this by removing the heat from the charged air, and cooler air is chemically denser than hot air, so it contains more OXYGEN, which creates more power. 5-stage intercooling is common with large power(electricity) production facilities using steam turbines.
And there are FUNDAMENTAL differences in how the two different "chargers" "charge" the air...
It is very important to grasp the concepts of HORSEPOWER and TORQUE, the differences between them, and other basics about Heat Engine Design. Mainly what on earth is Efficiency, Compression Ratio, bore and stroke, etc, etc...
It's even more important to understand what Enthalpy and Entropy are, and how they are used in the design of a thermodynamic heat engine...
If you can grasp those concepts, u will thoroughly understand how and why different engines use different methods of F/I.
In my opinion, as in Engineering Judgement, Turbochargers are the best way to increase power and efficiency of small engines. Regardless, of what someone thinks about "lag" , yes it is physically inherent, but from a purely theoretical view, turbos are more efficient... Mainly because of ONE reason. This is because they obtain the kinetic energy required to spin the compressor and charge the air for FREE, that is, it's redeemed from the exhaust gases, which would otherwise flow freely out of the exhaust...This is the MAIN difference between the two, the other differences are in packaging and how it attaches to the engine.
Yes, an exhaust wheel will slow the exhaust gases going through, but at the same time, an increase in cylinder pressure will offset the loss of power that would be associated with excess "back pressure"...
A turbo blowing the same amount of CFM or M^3/sec (air flow) as a supercharger, will provide more power theoretically, because there is no direct energy loss associated with the turbo, as there would be with the supercharger...
Now, after we determined that a turbo is more efficient, we can look at the reasons why Superchargers were developed...
Superchargers were developed because, while turbos are more effiecient, superchargers come in a smaller overall package, can be literally "bolted" on in place of the Intake Manifold, are cheaper to manufacture, and provide power without having to wait (for a turbine to surpass the surge limit. ie lag).
Superchargers were very popular on radial-piston aircraft engines, and they were used on planes like the B-29 superfortress, to develop 2200 HP from each engine. Not to mention, on V-engines, it's easier to mount a S/C than to run a two-turbo setup.
NOTE : Vortech superchargers and the like, operate like mechanically driven turbochargers (ie non-linear airflow delivery), so they can be compared to both turbos and Roots type superchargers (ie linear airflow delivery), and they have properties associated with the manner in which the charger recieves and provides it's power.

Some of the bad points of a supercharger include:
-Not being able to incorporate an intercooler (be it air/air, air/water, etc)
because the supercharger itself takes the place of the intake manifold, and sends the compressed charge directly through the valves. This leads to higher cylinder temperatures and less power because of the inability of hot air to effectively burn the octane of fuel provided. Now I know Vortech has an "aftercooler" for use with superchargers, but it's still not as efficient as an air/air intercooler traveling at 35mph, and most superchargers do not come with one.
-More mechanical mass, and therefore, more mechanical wear and tear, which leads to shorter life spans if comparable material is used. ( a titanium supercharger would last a LONG time, but be WAY TOO expensive, get it?)
-Constant boost pressure when driving, leading to increased gas mileage and increased wear and tear on engine itself.
-Not being able to instantly change the Pressure Ratio, (must change mechanical drive pulley)

Some good points of a turbo are:
-No parasitic loss of power to drive compressor wheel
-Ability to change boost, by regulating the air flow through a wastegate, at the touch of a finger.
-Ability to use Intercooling to decrease the amount of work that must be done to achieve the same outout, ie HP.
-Ability to drive with low/no boost and preserve gas mileage and reliability

Some of the bad points of a turbo system include:
-Many parts needed to complete turbocharging system (charge pipes, oil lines, coolant lines, wastegate, manifold, etc.)
-Lag, although, if your car is fast enough, it won't matter, cause u could just wait till boost hits, then rip off...Or just turn up boost and call it a day
-more parts that could be damaged, more parts=more probability something breaks or becomes problematic
-Much thought/engineering must be put into designing the cooling and oiling systems because of the extremely high-rpm of turbos.

And just for those who are Hell-bent on proving that superchargers are better, even though they're not, Just take one look at a Mazda RX-7 or a Supra TT from the late 90's, Those companies spent ALOT of money on R&D developing SEQUENTIAL turbo systems, to help eliminate the inherent turbo lag... Why wouldn't they use a supercharger?? Because simply put, it's not as efficient as a properly sized turbo for the intended power band (ie small turbo for low rpms, and big for high respectively).
Hope this helps clarify this age-old comparison.
Later