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The purpose of this page
is to answer some general questions about turbocharging. It is not
intended to be the be-all, end-all technical resource on turbocharging;
rather, this is a primer to help you understand the basics of
operation. We hope that you find this information useful.
What is a turbo?
Quite simply, a turbo is
merely an exhaust-driven compressor. Imagine a small shaft about the
size and length of a new pencil. Now rigidly attach a pinwheel to each
end of the pencil. One pinwheel (called the turbine) is placed in the
path of the exhaust gases which are exiting the engine. These gasses
are 'caught' in the turbine, causing it to spin. This in turn spins the
whole shaft, along with the pinwheel on the other end (called the
compressor). The compressor is placed in the intake air's path; once it
begins spinning, it actually compresses the air on its way into the
engine.
Why is this beneficial? Well, normally aspirated engines have to work
to draw in their intake air. In other words, as the intake valves open,
the piston's downward movement creates a vacuum which 'sucks in' some
air through the intake system. Ideally, the piston's movement would
suck in 100% of the air that could fill the combustion chamber. In the
real world this is not the case; the typical engine will draw in only
about 80% of the total volume of the combustion chamber. There are many
reasons for this--intake restrictions, valve timing, camshaft design,
and much more.
Now imagine that the
engine mentioned above has a turbocharger. When the turbo compresses
the air, it builds up pressure in the intake manifold. Now when the
intake valves open, air is actually forced into the combustion chamber.
(This is one reason why turbocharged engines are sometimes referred to
as 'forced-induction' engines.) As you might imagine, this allows more
air molecules to fill the chamber.
Okay, so now we have
more air molecules entering the engine. To benefit from this, we need
more fuel to match. On computerized vehicles such as these, various
sensors will "see" this amount of boost pressure and increase the
amount of fuel accordingly. Now that we also have more fuel entering
the engine, more power is made. (When you get right down to it, the
only way to make more power--on any engine--is to shove more of the
proper air/fuel mixture into the engine.)
How do turbochargers and
superchargers differ?
While they perform the
same function, turbochargers and superchargers go about it in
completely different ways. As has already been mentioned, a turbo is
driven by the exhaust gasses which are already being expelled from the
engine. So, in effect, turbos add 'free' power since their compression
is created by what was already discarded.
Superchargers, however, are different: they are belt-driven. They
feature a pulley whose belt is directly attached to the crankshaft,
this allowing them to spin in direct proportion to the engine itself.
The upside is a near absence of lag (see below); at least some boost is
typically available the instant you crack the throttle. The primary
drawback to a supercharger, however, is that they take power to make
power. The overall result is more power than there would be without the
supercharger; it's just that they aren't as efficient as a turbocharger
from an energy standpoint. Other drawbacks include lower mid-range
power than a turbo, lower thermal efficiency than a turbo, (sometimes)
much harder to incorporate intercooling, etc.
What is turbo lag (and
how do I avoid it)?
The majority of
turbochargers feature a wastegate--a valve which allows some of the
exhaust gas to be directed around the turbine. This allows the turbo's
shaft to spin at a reduced speed, promoting increased turbo life (among
other things). Think of it as a 'stand by' mode. Since the turbo isn't
needed during relaxed driving anyway, this effect is harmless...
...until you suddenly
want to accelerate. Let's say that you are loafing along, engine
spinning 1500 rpm or so. You instantly floor the throttle. The exhaust
gas flows through the turbo and cause it to spool (spin up to speed and
create boost). However, at this engine speed there isn't very much
exhaust gas coming out. Worse still, the turbo needs to really get
spinning to create a lot of boost. (Some turbos will spin at 150,000
rpm and beyond!) So you, the driver, need to wait for engine revs to
raise and create enough exhaust gas flow to spool the turbo. This wait
time--the period between hitting the throttle at low engine speed and
the creation of appreciable boost--is properly called boost response.
Many people incorrectly call it lag, which is really something
different. Lag actually refers to how long it takes to spool the turbo
when you're already at a sufficient engine speed to create boost. For
example, let's say your engine can make 12 psi at 4000 RPM. You're
cruising along at a steady road speed, engine spinning 4000 RPM, and
now you floor it. How long it takes to achieve your usual 12 psi is
your turbo's lag time. Between the two, slow boost response usually
causes the most complaints.
There are two aspects to
consider when dealing with boost response: engine factors and driver
factors. As far as engine factors go, there are many things which
affect turbo lag... although most are directly related to the design of
the turbo itself. Turbos can be designed to minimize lag but this
usually comes at the expense of top-end flow. In other words, you can
barter for instant boost response by giving up gobs of horsepower in
the upper third of your RPM range. (Behold the catch-22 in designing
one turbo for all uses.)
Driver factors are
another matter. You basically need to understand how a turbo works and
modify your driving style accordingly. To sum it up, don't get caught
with your pants down! If you feel that there may soon be a sudden need
for serious thrust, downshift until your engine speed is at least 3000
RPM. This way there will be noticeable boost almost as soon as you hit
WOT. If you are going up a hill at WOT around, say 1800 RPM and your
speed is dropping, you'll need to downshift just like any other car in
the same situation. Remember: turbos need exhaust gas in order to spin.
Let them have some when they need it.
What's an intercooler
and how does it help?
To answer that question,
a discussion of thermodynamics is involved. Turbos, as has been
mentioned, compress an engine's intake air. By laws of physics,
compressing air also heats it. For an engine, heating the intake air is
a bad thing. For one, it raises the combustion chamber temperature and
thus increases the chance of detonation (uncontrolled combustion which
damages your engine). Another bad thing is that air expands as it is
heated. So in other words, it will lose some of the compression effect
and the turbo must work harder to maintain the desired level of
compression.
Thus enters the intercooler into the equation. An intercooler is a heat
exchanger--sort of like a small radiator except that it cools the
charge (your intake air) rather than the engine coolant. Now that the
charge is being cooled, two benefits appear: combustion temperatures
decrease (along with the detonation), and the charge becomes denser
which allows even more air molecules to be packed into the combustion
chamber. Exactly how much heat is removed varies greatly; some factors
include the type of intercooler used, its efficiency, and its mounting
location. From what I've seen, getting your intake charge temperature
within 20 degrees of ambient is excellent; consider this a practical
limit for a street-driven car (meaning you might get closer but
probably not without spending tons of money).
There are two types of
intercoolers: air-to-air and air-to-water. Air-to-air means that as the
charge passes through the intercooler, the intercooler itself is cooled
by air flowing through its fins. Picture your car's radiator but
substitute the intake air where the coolant goes and you'll have a
rough idea of how it works. In an air-to-water intercooler, the
intercooler is cooled by a liquid rather than air; this liquid has its
own radiator placed where it can receive airflow, hoses connect this
radiator to the intercooler itself, and the liquid must be circulated
throughout the entire system.
Each type of intercooler
has its strength and weakness. Air-to-air units tend to require longer
ducting to route the air from the turbo through the intercooler then
back to the engine; this extra tubing might increase lag slightly on
mass-flow engines and may also present interesting packaging
challenges. Air-to-water units, however, can have significantly shorter
intake plumbing; the intercooler can be placed in hot underhood areas
where no airflow is present since the liquid coolant circulates to its
radiator. This allows for simpler installation but at an expense of
reduced cooling efficiency. Note that both kinds cool better when air
is flowing through the intercooler (air-to-air) or the radiator
(air-to-water); both kinds can benefit from the installation of a fan
for low-speed operation.
Which type is better?
Depends on your goal. From where I sit it seems that air-to-water
intercoolers are used either for convenience--to eliminate the possible
ducting nightmare of the intake--or for drag-only vehicles where a "one
shot" setup uses ice to actually drop charge air temps below ambient...
for a very short while.
Can I mount more than
one intercooler?
Sure you can; your
limits will be defined by the room you have to work with and your
budget. (Owners of mass-flow setups will need to keep an eye on the
total length of their intake plumbing.) If you try this, should you
mount your intercoolers parallel or in series? The correct answer is
simple: in parallel. ALWAYS. Mounting intercoolers in series doubles
your pressure drop, which is very bad, while mounting in parallel cuts
your pressure drop in half while also allowing for more thorough
cooling. Twin intercooling can cause great results, just like upgrading
to one large intercooler. A racer's rule of thumb states you can never
have too much intercooler.
Can I make my air-to-air intercooler more effective?
Certainly! What can be
done? For starters, maximize airflow through the intercooler. This
means remove anything between the incoming air and the intercooler's
fins--the A/C condenser, funky ducting, or anything else that actually
impedes airflow. If your intercooler isn't directly in the path of air,
relocate it so that it is. If you are unable to move it around, create
some sort of shroud/airdam to redirect air through the intercooler (tin
or plastic should be great for this).
Another idea for you
creative types is to make a mister. Get a windshield fluid reservoir,
mount it where it will stay cool, and fill it with water. Now run the
output tube to the intercooler. Mount a few spray nozzles aimed at the
front of the intercooler's core, then join them to the output line with
tees and such. Rig up this reservoir pump to a switch or button inside
the car so that you can momentarily enable it when desired. The water
evaporation will help draw even more heat off the intercooler, further
lowering the temperature of the intake air that flows through it. You
can get really fancy here; I had a friend that rigged the on/off switch
to the throttle body so that the mister would activate at WOT.
TURBOs FAQs
What are the main tuning problems when dealing
with Turbos? Engine calibration - fueling and ignition timing.
Under boost, it is crucial that there is no engine-killing detonation
occurring within the cylinder. This is done by fine tuning the air/fuel
ratio a bit rich to help cool the combustion gas, and by tuning the
ignition advance curve to ensure that combustion chamber pressures stay
below the level that causes unburned fuel to ignite ahead of the
advancing flame front.
What are the
main differences between a Single and Twin Turbo setup?
1. A single turbo
receives exhaust flow from and supplies air to all cylinders.
2. The most common type
of twin turbo setup is the parallel system where each turbo is fed by ½
of the engine's cylinders. Here, both compressors supply air to the
intake manifold simultaneously.
3. There are also
sequential twin turbo systems, which run on one small turbo at low
engine speeds and switch to two parallel turbos at a predetermined
engine speed and/or load.
4. Furthermore, there
are series twin turbo systems where one turbo feeds the other turbo.
These are primarily used on diesel engines due to the extremely high
boost levels that can be generated.
Choosing between a
single or parallel twin turbo setup is primarily based on packaging
constraints in the engine bay, or a personal choice by the tuner. In
most cases, for top performance, a single turbo is preferable because
larger turbos are generally more efficient than smaller turbos.
However, often there is not room for one large single, or the tuner
wants the visual impact of twin turbos. The notion that two smaller
turbos will build boost faster than one large turbo is not always
accurate because even though the turbos are smaller, each one is only
getting half of the exhaust flow. Sequential systems seem to have the
capacity to support big power. In theory, the sequential twin turbo
setup is a potent combination. A few O.E.s have produced systems of
this type but control issues have proven significant, making them
challenging to function seamlessly. One slight draw back to a
sequential twin turbo system is that sometimes during daily driving
(specifically, in cornering) if the driver is not constantly aware, the
second turbo will spool and result in a lot of unpredicted power.
What is Turbo
Lag? Turbo lag is the time delay of boost response after the
throttle is opened when operating above the boost threshold engine
speed. Turbo lag is determined by many factors, including turbo size
relative to engine size, the state of tuning of the engine, the inertia
of the turbo's rotating group, turbine efficiency, intake plumbing
losses, exhaust backpressure, etc.
What is Boost
Threshold? Boost threshold is the engine speed at which there
is sufficient exhaust gas flow to generate positive manifold pressure,
or boost.
What is a boost
leak? A boost leak means that somewhere in the turbo or
intake, there is an area where the air (boost) is escaping. Typically a
boost leak is caused by a loose or bad seal, cracked housing, etc. When
a boost leak is present, the turbo will be able to generate boost, but
it may not be able to hold it at a constant level and pressure will
drop off proportionally to the size of the leak.
How can I adjust
the turbo boost? Adjusting the boost is straightforward.
However, it depends on the type of boost controller.
1. For a standard
Wastegate actuator, simply recalibrate the actuator to open (more or
less) for a given pressure. Changing the length of the rod that
attaches to the
2. Wastegate lever
accomplishes this adjustment.
For mechanical boost
control systems, adjustments may involve changing the setting on a
regulator valve(s).
3. For electronic boost
control systems, adjustments may need to be made to the vehicle's
engine management system.
4. For an external
Wastegate, adjusting the boost often requires turning the adjustment
screw (when equipped) to increase/decrease spring load, changing
Wastegate springs, or shimming Wastegate springs.
IMPORTANT:
WHILE ADJUSTING THE BOOST IS
STRAIGHTFORWARD, THIS CHANGE REQUIRES MODIFICATIONS TO THE ENGINE FUEL
MANAGEMENT SYSTEM AND ECU!
What is boost
spike? A boost spike is a brief period of uncontrolled boost,
usually encountered in lower gears during the onset of boost. Typically
spikes occur when the boost controller cannot keep up with the rapidly
changing engine conditions.
What is boost
creep? Boost creep is a condition of rising boost levels past
what the predetermined level has been set at. Boost creep is caused by
a fully opened Wastegate not being able to flow enough exhaust to
bypass the housing via the Wastegate itself. For example, if your boost
is set to 12psi, and you go into full boost, you will see a quick rise
to 12 or 13psi, but as the rpm's increase, the boost levels also
increase beyond what the boost controller or stock settings were. Boost
creep is typically more pronounced at higher rpm's since there is more
exhaust flow present for the Wastegate to bypass. Effective methods of
avoiding or eliminating boost creep include porting the internal
Wastegate opening to allow more airflow out of the turbine, or to use
an external Wastegate.
What is
compressor surge? The surge region, located on the left-hand
side of the compressor map (known as the surge line), is an area of
flow instability typically caused by compressor inducer stall. The
turbo should be sized so that the engine does not operate in the surge
range. When turbochargers operate in surge for long periods of time,
bearing failures may occur. When referencing a compressor map, the
surge line is the line bordering the islands on their far left side.
Compressor surge is when the air pressure after the compressor is
actually higher than what the compressor itself can physically
maintain. This condition causes the airflow in the compressor wheel to
back up, build pressure, and sometimes stall. In cases of extreme
surge, the thrust bearings of the turbo can be destroyed, and will
sometimes even lead to mechanical failure of the compressor wheel
itself. Common conditions that result in compressor surge on
turbocharger gasoline engines are:
1. A compressor bypass
valve is not integrated into the intake plumbing between the compressor
outlet and throttle body
2. The outlet plumbing
for the bypass valve is too small or restrictive
3. The turbo is too big
for the application
How does a
Wastegate work? A Wastegate is simply a turbine bypass valve.
It works by diverting some portion of the exhaust gas around, instead
of through, the turbine. This limits the amount of power that the
turbine can deliver to the compressor, thereby limiting the turbo speed
and boost level that the compressor provides.
1. The Wastegate valve
can be "internal" or "external". For internal Wastegates, the valve
itself is integrated into the turbine housing and is opened by a
turbo-mounted boost-referenced actuator.
2. An external Wastegate
is a self-contained valve and actuator unit that is completely separate
from the turbocharger.
3. In either case, the
actuator is calibrated (or set electronically with an electronic boost
controller) by internal spring pressure to begin opening the Wastegate
valve at a predetermined boost level.
4. When this boost level
is reached, the valve will open and begin to bypass exhaust gas,
preventing boost from increasing.
What is the
difference between a BOV and a Bypass Valve? How do they work, and are
they necessary? A Blow Off Valve (BOV) is a valve that is
mounted on the intake pipe after the turbo but before the throttle
body. A BOV's purpose is to prevent compressor surge. When the throttle
valve is closed, the vacuum generated in the intake manifold acts on
the actuator to open the valve, venting boost pressure in order to keep
the compressor out of surge. Bypass valves are also referred to as
compressor bypass valves, anti-surge valves, or recirculating valves.
The bypass valve serves the same function as a BOV, but recirculates
the vented air back to the compressor inlet, rather than to the
atmosphere as with a BOV.
How should I
break in a turbo? A properly assembled and balanced turbo
requires no specific break-in procedure. However, for new installations
a close inspection is recommended to insure proper installation and
function. Common problems are generally associated with leaks (oil,
water, inlet or exhaust).
What is/causes
Shaft Play? Shaft play is caused by the bearings in the center
section of the turbo wearing out over time. When a bearing is worn,
shaft play, a side to side wiggling motion of the shaft occurs. This in
turn causes the shaft to scrape against the inside of the turbo and
often produces a high-pitched whine or whizzing noise. This is a
potentially serious condition that can lead to internal damage or
complete failure of the turbine wheel or the turbo itself.
What is causing
my turbo to sound like a sewing machine's whistle? The "sewing
machine whistle" is a distinct cyclic noise cause by unstable
compressor operating conditions known as compressor surge. This
aerodynamic instability is the most noticeable during a rapid lift of
the throttle, following operation at full boost.
I want to make x
horsepower, which turbo kit should I get? or Which turbo is best?
Select a turbocharger to achieve desired performance. Performance
includes boost response, peak power and total area under the power
curve. Further decision factors will include the intended application.
The best turbo kit dictated by how well it meets your needs. Kits that
bolt on without any modification are best if you don't have fabrication
capabilities. Less refined kits can be cost effective if you access to
fabrication capabilities. For more information on the right
turbocharger for you, please contact Xcceleration.
Does my turbo
require an oil restrictor? Oil requirements depend on the
turbo's bearing system type. Some types of turbos have two types of
bearing systems; traditional journal bearing; and ball bearing. The
journal bearing system in a turbo functions very similarly to the rod
or crank bearings in an engine. These bearings require enough oil
pressure to keep the components separated by a hydrodynamic film. If
the oil pressure is too low, the metal components will come in contact
causing premature wear and ultimately failure. If the oil pressure is
too high, leakage may occur from the turbocharger seals. With that as
background, an oil restrictor is generally not needed for a
journal-bearing turbocharger except for those applications with
oil-pressure-induced seal leakage. Remember to address all other
potential causes of leakage first (e.g., inadequate/improper oil drain
out of the turbocharger, excessive crankcase pressure, turbocharger
past its useful service life, etc.) and use a restrictor as a last
resort. Tuners can tell you the recommended range of acceptable oil
pressures for your particular turbo. Restrictor size will always depend
on how much oil pressure your engine is generating-there is no single
restrictor size suited for all engines. Ball-bearing turbochargers can
benefit from the addition of an oil restrictor, as most engines deliver
more pressure than a ball bearing turbo requires. The benefit is seen
in improved boost response due to less windage of oil in the bearing.
In addition, lower oil flow further reduces the risk of oil leakage
compared to journal-bearing turbochargers. Oil pressure entering a
ball-bearing turbocharger needs to be between 40 psi and 45 psi at the
maximum engine operating speed. For many common passenger vehicle
engines, this generally translates into a restrictor with a minimum of
0.040" diameter orifice upstream of the oil inlet on the turbocharger
center section. Again, it is imperative that the restrictor be sized
according to the oil pressure characteristics of the engine to which
the turbo is attached. Always verify that the appropriate oil pressure
is reaching the turbo. The use of an oil restrictor can (but not
always) help ensure that you have the proper oil flow/pressure entering
the turbocharger, as well as extract the maximum performance.
How much shaft
play should my dual ball bearing turbo have? The full
ball-bearing turbo is designed to have clearance between the bearing
cartridge and center housing for hydrodynamic damping in addition to
the internal clearances of the bearing cartridge itself. Hydrodynamic
damping uses the incompressible properties of a liquid (oil in this
case) and the space around the bearing cartridge to dampen the shaft
motion of the rotating assembly. When the turbo is new, or has not
operated for a long period of time allowing most of the oil to drain
out, the rotating assembly will move more in the radial direction than
a typical journal-bearing turbo because there is no oil in the center
housing. This condition is normal. As long as the shaft wheel spins
freely and the wheels don't contact their respective housings, the
assembly will function properly.
What other systems are affected by turbocharging? (Fuel, Oil, Cooling,
Drivetrain, etc)
There are several factors that must be addressed when deciding to
turbocharge a previously naturally aspirated engine, such as: Is the
current fuel delivery system capable of providing increased, adequate
amounts of fuel? Is the cooling/oiling system capable of handling the
extra power and consequently, extra heat that is generated by the
turbo? Is the clutch/transmission/drivetrain up to the task of handling
the extra power? Etc
OTHER
FAQs
How is boost
measured? (Bar, mmHg, PSI) and How do you convert from one to another?
Boost is measured as the pressure that the turbo creates above
atmospheric pressure.
Normal Atmospheric Pressure (1 atm) = 14.7 psi = 760 mm Hg
1 Bar is not actually equal to 14.7 psi, but rather it is equal to 14.5
psi, = 0.9869 atm = 750.062 mm Hg
The turbo gauges
measures turbine speed, right?
The "turbo gauge", commonly called a boost gauge, does not measure
turbine speed. It measures the intake manifold pressure. Under light
loads the boost gauge will indicate a vacuum due to the turbocharger
shaft not rotating fast enough to create positive pressure (boost).
Once load (throttle position) increases, the boost gauge will indicate
a positive pressure.
What is a boost
controller?
A boost controller is a device that bleeds or blocks the boost pressure
signal entering the Wastegates actuator. The idea is to keep the
Wastegates closed to allow higher boost pressures than the actuator
would otherwise allow. These can be simple mechanical or sophisticated
electronic devices, with price tags to match.
Which boost
controller should I get? (Manual or Electronic)
Boost controllers vary widely in performance, price, and functionality.
We have found the manual boost controllers simple and easy to setup, as
long as your engine is capable of handling constant boost and is tuned
properly. Electronic boost controllers are more complicated, able to
dial in boost for each gear and handle high boost with proper tuning.
As to which one is best for your application, we suggest discussing
your application with us.
How much boost
can I run on pump gas?
The primary limitation to maximum boost is engine knock. It is also not
advisable to run the maximum amount of boost your car can handle on a
daily driven basis as a precaution against if the boost spikes. If your
car's manual states to use premium fuel, do not use regular!
- What is Knock/Detonation?
Knock is a condition caused by
abnormal combustion of the air/fuel mixture and can result in damage to
an engine.
The three factors that result in engine knock are:
1) knock resistance
characteristics (knock limit) of the engine
2) ambient air conditions
3) octane rating of the
fuel being used
Since every engine is
vastly different when it comes to knock resistance, there is no single
answer to "how much." Design features such as combustion chamber shape,
spark plug location, bore size and compression ratio affects the knock
characteristics of an engine. In addition, engine calibration of fuel
and spark plays an enormous role in dictating knock behavior.
For the turbocharger
application, both ambient air conditions and engine inlet conditions
affect maximum boost. Hot air and high cylinder pressure increases the
tendency of an engine to knock. When an engine is boosted, the intake
air temperature increases thus increasing the tendency to knock. Charge
air cooling (e.g. an intercooler) addresses this concern by cooling the
compressed air produced by the turbocharger.
The octane rating of
fuel is a measure of a fuel's ability to resist knock. The octane
rating for pump gas ranges from 85 to 94 while racing fuel would be
well above 100. The higher the octane rating of the fuel, the more
resistant it is to knock. Since knock can be damaging to an engine, it
is important to use fuel of sufficient octane for your application.
Generally
speaking, the more boost you run, the higher the octane requirement.
Should I run a
Turbo Timer?
A turbo timer enables the engine to run at idle for a specified time
after the ignition has been turned off. The purpose is to allow the
turbo to cool down thus avoiding "coking" ("coking" is burned oil that
deposits on surfaces and can lead to blocked passages).
The need for a turbo timer depends on how hard the turbo and engine is
used. Running at full speed and full load then immediately shutting
down (heat soak) can be extremely hard on a turbo.
June 2001 TechTIPS
published by Subaru for Subaru Technicians
(http://www.subaruwest.com/PDF_files/Tech_PDF_Folder/june_2001_techtips.pdf)
states:
"2002 WRX TURBO COOL DOWN
PROCEDURE"
FHI's position regarding
this is that it is not necessary to perform a "cool down/idling"
procedure, as was recommended with past turbo models. Our current 2.0L
turbo engine has a far greater cooling capacity and, coupled with
technology advances, makes this practice no longer necessary. This
explains why information about cool down is not included in the 2002MY
Impreza Owner's Manual or newer.
"The heat contained in
the turbo charger will begin to vaporize the coolant at the turbo
charger after the engine is stopped. This hot vapor will then enter the
coolant reservoir tank which is the highest point of the coolant
system. At the same time the vapor exits the turbo charger, coolant
supplied from the right bank cylinder head flows into the turbo. This
action cools the turbo charger down. This process will continue until
the vaporizing action in the turbo charger has stopped or cooled down."
Water-cooling
of the turbocharger's center housing has essentially eliminated the
need for turbo timers or extended idling periods (which are OEM on
Subarus).
Do I really need
the cool down procedure on my turbo?
The need for a cool down procedure depends on how hard the turbo and
engine is used, and whether or not the turbo is water-cooled. All
Garrett turbochargers must pass a heat soak test and the introduction
of water-cooling has virtually eliminated the need for a cool down
procedure. Garrett is one of the few turbocharger manufactures that
subjects their turbos to several OE qualification tests. When you buy a
Garrett turbo you can be sure it's a reliable one!
How can I remove
and clean the oil condensation box/oil catch can?
The oil condensation box, or catch can, can be cleaned once it is
removed with any cleaning solvent. Simply fill the box with a cleaner
and slosh it around until oil deposits are gone. Removing the oil
condensation box can be a challenge and varies by vehicle.
NOTE: some vehicles are not equipped with an oil condensation box.
What is the
purpose of an oil catch can?
An oil catch can's purpose is to catch oil blow-by gasses that can
eventually create a carbon and oil sludge build-up in the intake and
turbo.
What additional
maintenance is required for the turbo?
Good, clean oil is extremely important to the turbocharger. It is best
to change the oil and filter at least as often as the automobile
manufacturer recommends.
Turbo performance is
sensitive to turbo inlet conditions. A clogged air filter can
drastically affect the turbo inlet. Air filters should be inspected at
every oil change and replaced at 12,000 to 15,000 mile intervals.
NOTE:
Never exceed the vehicle manufacturer's recommended filter change
intervals.
What compression
ratio should I run with my turbo engine?
Allowable compression ratio depends on many factors, and there is no
one right answer for every application. Generally, compression ratio
should be set as high as feasible without encountering detonation at
the maximum load condition. Setting the compression ratio too low will
result in an engine that is a bit sluggish in off-boost operation.
Setting it too high however, can lead to serious engine problems due to
knock.
Factors that influence
the compression ratio can include: fuel anti-knock properties (octane
rating), boost pressure, intake air temperature, combustion chamber
design, ignition timing, and exhaust backpressure. Many modern engines
have well designed combustion chambers that will allow modest boost
levels with no change to compression ratio, assuming appropriate
tuning. For higher power targets with more boost, compression ratios
should be adjusted to compensate.
How do I adjust
my compression ratio?
The easiest and most effective way to accomplish this is through the
use of either higher/lower compression pistons, and/or using a head
gasket of a different thickness.
Should my
turbo/exhaust manifold glow red after driving?
Yes, the turbo/exhaust manifold can glow red under certain driving
conditions. The exhaust gas temperature can reach over 1600F under high
load operating conditions; i.e. towing, extended uphill driving, or
extended high rpm/boost conditions.
What should I
look out for when buying a turbo?
1. Condition of the
turbine housing - inspect for cracks on the exterior and inside the
inlet of the housing. If the housing has cracks then the housing needs
to be replaced.
2. Condition of the
turbine and compressor wheels - inspect for cracks and damaged blades.
If either of the wheels are damaged then the wheel (s) need to be
replaced and the center section balanced.
3. Condition of the
bearings - spin the turbocharger shaft and check for roughness. If
roughness is detected then the turbocharger needs to be disassembled
and the internal components inspected and replaced if necessary.
4. The most important
factor is to make sure the turbo is the proper one for your
application. A properly matched turbo will provide better performance
and more reliable operation. A properly matched turbo includes matched
turbine and compressor wheel sizes and appropriate housings.
Are oil deposits
indicative of impending turbo failure? There is blue/black smoke, is my
turbo going bad?
Blue/black smoke can be caused by numerous conditions, and one of them
could be a turbocharger worn past its useful service life. The
following are potential reasons that blue/black smoke could occur:
1. Clogged air filter
element or obstructed air intake duct. This condition creates a vacuum
due to high differential pressure resulting in oil drawn into the
compressor and subsequently burned during engine combustion.
2. Engine component
problems; i.e. worn piston rings or liners, valve seals, fuel pump,
fuel injectors, etc.
3. Obstructed oil drain
on turbocharger resulting in pressure building inside the center
housing and forcing oil past the turbocharger seals
4. Damaged turbocharger
or turbocharger worn past its useful service life
5. Black smoke is also
sometimes indicative of too rich an air/fuel mixture.
How fast will my
car go with xyz?
This question cannot be answered as how fast any given car will go
depends on the unique individual setup, road/weather conditions, and of
course, the driver's skill.
What is the
Inducer?
Looking at a compressor wheel, the inducer is the "minor" diameter. For
a turbine wheel, the inducer is the "major" diameter. The inducer, in
either case, is where flow enters the wheel.
What is the
Exducer?
Looking at a compressor wheel, the exducer is the "major" diameter. For
a turbine wheel, the exducer is the "minor" diameter. The exducer, in
either case, is where flow exits the wheel.
SUBARU
Service Bulletin for Turbo Cars
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