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PART 1: TURBO BASICS
- The exhaust gases exit through the exhaust manifolds or headers and
into the Turbo.
- Exhaust gases then move the Turbine wheel and exit the housing through
the exhaust pipes and to the atmosphere.
- The Turbine and Compressor Wheels are joined by a shaft which is lubricated
by engine oil.
- The compressor wheel pulls the filtered ambient air and compresses
- The compressed air then moves into an intercooler to cool the air
- After the intercooler, the air charge moves into the Throttle body
- The Compressed air charge enters the cylinders in a "compressed
state" and so it enables the engine to draw more air into the chambers,
this "synthetic" increase in compression is called "dynamic
compression" or in other terms "forced induction".
- This increased compression enables the engine to behave like a larger
Typical Turbo System Parts
Turbo: Complete housing with Wastegate,
Turbine and Compressor
Intercooler: cools Compressed air
Wastegate: Valve that controls the
boost amount by releasing exhaust gases to the exhaust before they
reach the turbine.
FUEL: One of the priciples of internal
combustion engines is that for any amount of fuel there's a need for
a given air charge.
In the case of Turbos AND supercharger systems, the Increased
air charge needs a proportional increase in fuel delivery. The consequence
of a LEAN air fuel mixture (or lack of fuel) is called Detonation.
Detonation is the main concern on forced induction engines
since it can cause severe damage to the engine.
On a stock 5.0 liter the fuel injectors are small, and
at medium boost levels, the 19lph (pounds per hour) stock fuel injectors
might not be enough to compensate for the increase in air charge.
COOLING: Another point of high importance
is to make sure your cooling system is operating properly, the increased
compression at the cylinder heads will cause an increase in engine temperature.
EXHAUST: The increase in exhaust flow
and turbo backpressure makes very important to have a good exhaust system,
what goes in must go out.
IGNITION: With the increase in cylinder
pressure, a better spark will be needed to ignite the air/fuel mixture.
This can be achieved by reducing plug gap and/or installing an aftermarket
ignition system or a better coil. At low boost levels reducing plug
gap could be the only needed ignition modification.
Twin Turbo and Single Turbo selection
Before you start the search for a TURBO, there are some
considerations you might need to address first:
Will it be a single or twin setup?
How big a Turbo do i need?
For any given Turbo model are there any variations?
What about intercoolers?
To answer some of these questions lets just say that you
have to choose your turbo(s) depending on their capabilities, a small
Turbo such as the ones you find in small displacement engines like a
Nissan 1.3L will be too small for a V8 5.0 or 4.6. Others such as DIESEL
engine Turbos might be too big.
In order to help you decide what brand-type of turbo you
need, the next application can help you a lot.
Engine type: select gasoline (or diesel
if you have a 5 ton truck)
Number of Turbos: its your choice, we will
later explain some pros-cons of both setups.
Intercooler: YES, this is the most efficient
setup, you won't regret it.
Engine Capacity in CC's: for both 5.0 and
4.6 select 5,000
Maximum RPM: again your choice...will depend
a lot on your actual modifications.
For a Stock 5.0 or 4.6 select 6,000 +/-
BOOST: how much you want/need? a safe limit
for a STOCK 5.0 or 4.6 will be 8psi.
Now that you selected your dream setup you might have
the following results:
Note that for every type of Turbo there are different
"trim" versions, each trim has different turbine and compressor
designs that promote a given characteristic such as volumetric efficiency,
Both setups have almost the same BHP capabilities, but
there are some pro's and con's to each setup.
A Twin turbo setup will probably be more efficient than
a single one at low RPMs but it is certainly more difficult to install.
The single turbo setup could have lower boost at low RPMs
but a bit more on top and is easier to maintain and install.
This considerations could be affected by several variables,
compressor and turbine design, piping, intercooler efficiency, etc.
But consider the above assumptions as "valid" for most "stock"
turbos you will find in a junkyard.
There are some guidelines you might want to follow, choose
and intercooler that was designed for an engine as big as yours (5.0L,
4.6L, etc), or BUY 2 with half the displacement of your engine. You
could place each intercooler in sequence one after the other or have
someone weld them together.
Don't restrict your search to Gasoline engine coolers,
probably a Turbo diesel engine intercooler is what you need.
This ends part 1 of our Turbo How to series, we hope the
provided info will prove itself useful. We would like to hear your comments
and suggestions on the subject.
We want to keep this pages updated as much as possible,
so if you find any inconsistencies, errors or want to suggest something,
don't hesitate to do so.
END of PART 1
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