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RB25 and RB2O

Blow off valve

270 degree thrust bearing

ball bearing conversion




A turbo can only work reliably and efficently
if all the components are matched and adjusted
correctly.This page will explain the critical
components assuming the basic system is understood.


Is mainly just a centrifical air pump driven
by exhaust gasses.there are many models
and designs.The latest designs feature
Ball Bearing ,ceramic turbine wheels,
variable nozzle turbine(VNT)and some
even have plastic compressor wheels.


A device to bypass the high pressure exhaust
gasses around the turbine to stop the turbo
from increasing speed which stops any more boost
pressure from increasing.Most smaller
Turbochargers have wastegates built into the
exhaust housing.External wastegates are mainly
on higher horsepower engines to allow more flow.


Compressing any air creates heat,less heat
means less expansion and more denser,
meaning more air in reserve to enter the engine.
An intercooler is an air radiator to cool
down boost.A too large intercooler does
create turbo lag as boost needs to fill up the
tube volume before it gets to the engine.


This device is a protection device for the
turbo on systems where the throttle plate is down
steam from the turbo.On boost,while the turbo is
screaming at say 200,000 rpm, a sudden blockage
down stream(from lifting the throttle) causes a
massive shockwave and boost spike.The
turbo can't stop spinning that quick so the
boost can only escape through the compressor
wheel blades which are spinning in the opposite
direction.So without a blowoff valve or an
incorrectly adjusted one, big demage can occur to
the compressor wheel and thust bearing.A loosely
adjusted and large blowoff valve is better
for reliability but it can effect gear changes
from releasing too much boost,a balance
is needed.


Turbochargers spin incredibly fast and hot
so they need good oil supply.any turbo engine
needs regular oil changes to keep the oil
fresh.Poor oil quality can't handle the heat
and it causes carbon build up inside the turbo
bearing housing causing oil drain blockages,
oil feed blockage,slow rotor spooling,eccessive
heat. Too much oil pressure causes the standard
oil drainage to not handle the volume and backs
up to reach the seals (which are only piston rings)
and leak(smoke).Too little oil pressure can stop a
bush bearings from "floating"and cause the
bearings to wear out. Ballbearing turbo's don't
need a lot of oil pressure as they are ball
bearings instead of bush bearings but still can't
suvive on NO oil.many turbo's come in for
repairs because of oil leaking out of the housings
and smoking ,but once stripped nothing is found
wrong with it so the question is raised "What's
wrong with the engine?"Basically if this is the
case it is an oil drainage issue.Something
is not letting the oil drain back to the sump easily.
On cars fitted with an aftermarket turbo usually
the oil drain is modified,
Also the sump breathing must be looked at as
high horsepower engines or even engines that have
had an increase in power must have good sump
breathing this helps improve horsepower also.
There are internal tricks that can help on turbo's
to increase oil drainage and keep oil away
from seals but not always preventable .
A false statement lots of people say when
explaining the problem with there turbo is "I think
it blew a seal",You can't blow a seal on a turbo
they are a piston ring in a groove with no pressure
behind it ,the problem is usually oil drain back.
A blown piston in the engine could cause a turbo
to leak oil in the housings (smoke)due to blowbye
through the piston rings and the breathers
can't handle it. Thrust failure causes oil leaks
also.If there is axial movement (in and out)then
this causes demage to many internal parts
(see blowoff valves)A blocked air cleaner is
another reason for oil leaks,but only in the
compressor end.The blockage creates a
vaccuum and piston rings don't like it and leak.
that is why they make carbon seals for the
compressor end seals.They are a very good seal
but do slow the spool up a little.
In the days before EFI,carbon seal turbo's were
common because of a carburator attached to the
front of the turbo.


The thrust bearing keeps the rotor in position,
it needs plenty of lubrication due to the huge thrust loads applied to it. Most turbo's come standard
with thrust shaped to a 270° radius.This is fine
for standard cars but high horspower engines
need at least 360° bearings.This spreads the load over larger surface area which is less stress
on the metal. 360° Bearings are in some factory
turbo's and if more thrust strength than that is needed ball bearings are required.


There is no doubt ball bearing turbo's are
superior to journal bearing. They spool up quicker
and can handle huge thrust loads on low oil
pressure. The bearings are angular contact
bearings which replace the journal bearing and
the thrust bearing. Because of the lack of thrust
bearing the drag is less which gives better
spool up. Many manufacturers supply ball
bearing turbo's(seelinks)and some aftermarket
companies offer their version also.
Custom Ball Bearings here-projects
also see Custom Ball Bearings in Performance


This is is one of the very latest turbo designs.
It's called the variable nozzle turbo because
the nozzle area,which is the gap just before
the turbine wheel tips has variable vanes to
change the angle of approach of the gasses to the
wheel tips,the wider the angle the slower the
speed and the sharpest is the fastest. Some
cars operate this off the vaccuum of the manifold
meaning the highest vaccuum is the fastest
spool up. All this is to overcome the "LAG"
which turbo's have a knowm problem of. VNT
turbo's are not so common on the aftermarket
seen yet.


This action is critical to a turbo shaft
considering they spin at about 200,000 rpm and more.
The balancing is done in a 5 step proceedure
        1.compressor wheel
2.turbine wheel
3. rotor
4. core
5. VSR

Every time a shaft is removed it must be rebalanced. Disturbing the secured compressor
wheel throws it out of balance. An out of balance
rotor wears out the journal bearings fast.There
is no reason under normal operation that a turbo rotor will go out of balance unless it is chipped
on the blades on either end of the rotor or blasted
from particals (like sand).


Is when the compressor wheel flow rate exeeds
engine or what is asked of the compressor wheel
falls outside the flow chart of the compressor
wheel. It sounds like a choofing noise and can
make the boost gauge fluctuate. Surging causes
demage to the compressor wheel and thrust,
check the flow chart of the compressor wheel
before deciding on a hiflow of a turbocharger.
(see links for compressor chart site)


Hitachi Turbo

Tial Wastegate

Evo with intercooler

mounted blow off valve

TO4 cutaway

demaged parts

Piston ring seal and carbon seal

360 degree thrust bearing

Journal bearing compared to a Ball Bearing


Fine Balancing

T70 compressor map