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NORMALLY ASPIRATED (also known as NT,
non-turbo)
Examples: Chevrolet Corvette, Ford Ranger, Buick Park Avenue.
A normally aspirated car is one without any compression of the inbound air
before reaching the cylinders. Air is brought in through the air filter, sucked
into the combustion chamber, intake valve(s) close, sparkplugs ignite the fuel &
air and combustion occurs. Exhuast valve(s) open and the exhaust gas is
released, exiting out the exhaust manifold through the catalytic converter and
exhaust piping to the muffler.
TURBOCHARGED
Examples: Porsche 911 Turbo, Eagle Talon TSi, Dodge Daytona ES Turbo.
A turbocharged engine makes use of the hot escaping exhaust gases that the
normally aspirated engines 'waste'. On a turbocharger, there are two turbine
wheels very close to each other, and they are linked via a solid metal shaft.
One turbine connected to intake side of the motor while the second one is in the
path of the exhaust gases. As exhaust gases pass by the exhaust turbine on the
turbo, the force of the rushing air spins the turbine. Well, since the two are
linked, this means the intake turbine begins spinning at the same time, forcing
more air into the engine. This cycle, however, is dangerous; more air into the
engine makes more exhaust gases which spins the exhaust turbine which spins the
intake turbine which pushes more air into the engine. See what can happen? It's
like a small runaway nuclear explosion. If you keep your foot all the way to the
floorboard, the turbo would build so much pressure up in your engine that you
will blow your engine up. To prevent this, there is a valve in the exhaust
turbine housing that opens at a certain pressure to allow air to pass by the
exhaust turbine without increasing the turbine's speed (this valve is called the
"wastegate".)
Turbocharged cars typically have a intercooler
in between the turbo and the intake manifold. The intercooler is designed like a
radiator for the air passing through; air leaving the turbo is extremely hot
(the exhaust gases rushing through the turbo can reach temperatures well over
1600 degrees.) Cooler air is more dense, contains more oxygen (and other gases)
per volume, and combined with more fuel means more horsepower.
The problem with a turbo is that it requires
exhaust gases to get it moving, so the car has to be moving. And from the time
you press the gas to the floor to the time you get a response is called 'turbo
lag'. While a properly tuned turbocharger, this lag is minimal but still
present.
SUPERCHARGED
Examples: Pontiac Grand Prix GTP, Pontiac Bonneville SSEi, Ford 150 SVT
Lightning.
Supercharged cars do what turbocharged cars do, they force air into the motor,
but in a different fashion. To get additional air in the engine without the
turbo lag, someone designed a roots-type rotor that sits on top of the motor and
runs off of a belt, just like the water pump and alternator. As the engine
spins, the supercharger spins just as fast as the crankshaft spins (or possibly
slower if underdrive pulleys are used.) There are also different designs of
superchargers; some are a bolt-on accessory that sits in the front on the motor
just like any other belt-feed item like the power steering pump or alternator.
With this design, are in sucked in one side from the air filter and forced down
a tube in the other direction and into the intake manifold. This is typically an
aftermarket supercharger, not originally sold with the car at production time.
There are drawbacks to a supercharger. First, a
decent well designed supercharger is more expensive than the largest and most
powerful turbocharger sold for street cars. Second, because a supercharger runs
off of a belt, it takes horsepower away from the motor to operate just like the
air conditioning compressor. In high performance situations, this can be
anywhere from 25 or 50 horsepower lost up to losing 200+ horsepower JUST to spin
the supercharger. Third, a supercharger gradually increases the PSI of boost in
the cylinders with increased rpms. You can only get max boost at the redline.
With a turbo, the turbo spools and the wastegate opens up once the peak desired
boost is reached (on street cars this is usually around half way to the red line
or lower.) Fourth and finally, a supercharger generally can not produce boost
pressure as efficiently as turbocharger can.
| AIR FLOW
THROUGH STOCK ENGINES WITH COMPLETE EXHAUST SYSTEMS |
| |
Normally Aspirated |
Single Turbocharger |
Supercharged |
| 1 |
Air filter |
Air filter |
Air filter |
| 2 |
Intake manifold |
Intake turbine on turbocharger |
Supercharger |
| 3 |
Combustion chambers |
Intercooler (with most turbos) |
Intake manifold |
| 4 |
Header(s) |
Intake manifold |
Combustion chambers |
| 5 |
Exhaust system |
Combustion chambers |
Header(s) |
| 6 |
|
Exhaust manifold(s) |
Exhaust system |
| 7 |
|
Exhaust turbine on turbocharger |
|
| 8 |
|
Downpipe |
|
| 9 |
|
Exhaust system |
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