This site is part of the 3SG History project.
setups / diagrams / pictures
the Turbo / Intercooler stuff works
The drawing below (from
the Garrett pages) shows the typical Turbo / Intercooler live-circle. Please
note that there are no fuel parts necessary to understand the prinziple.
So, how does the thing work ??
The engines cylinder exhaust gases travel out of the exhaust valves to the Turbo.
The gases speed then drives the large Turbine Wheel and leave the circle through the cats and
On the same axle as the gas-driven Turbine Wheel sits the Compressor Wheel (the axle is lubed by
the engines oil).
This smaller but more
tricky wheel has the same rpm like the Turbine Wheel and compresses the
filtered and measured air.
Compressing anything increases its temperature and therefore the compressed air has to be cooled
For this we let the air
travel through an Intercooler. This reduces the air temperature before
going back into the engine.
Why do we need an Intercooler??
Each engine has an
optimal temperature operating range. As our different ambients can vary
sooo much, the engine computers also measure barmoetric pressure, air temperature
and amount of air the engine sucks in. With this the optimal amout if air/fuel
ratio for the current ambient is determined and the engine runs in its
Fact: The more heat
the engine is getting the less power is produced. For design purposes it
is also desired to minimize the variable "intake temperature" as much as
possible. But we learned that compressing the air produces heat ! And the
more the air is compressed the more heat is produced. Therefore somebody
had the idea to cool down the compressed air ... the Intercooler was born.
With this element the air is cooled down to acceptable temperatures and
allows us freaks to increase the boost without the danger to loose the
needed horses. Of course, cooling the engine always helps to keep it longer
What is a wastegate ??
Its name says all....
a gate that is able to waste something away. Physics tells us that the
faster the turbine wheel turns the faster the compressor wheel turns and
therefore the more air will be transported. Also the compression increases
due to the speed. Of course, this depends on the style of the compressor
wheel, housing and whatever as the boost and rpm curve are not linear together.
But this will be dicussed sometimes later...
The wastegate now is
a device that can control the boost by releasing (wasting) some amount
of the exhaust gases to the exhaust BEFORE traveling to the Turbine Wheel.
Therefore the Compressor Wheels is not driven that fast and boost is reduced.
The wastegate is opened by a actuator, driven by air pressure. The actuator
is preloaded with a spring and opens the wastegate when the pressure applied
exceeds the springs load.
Usually the Compressors
output will be connected by a vacuum hose to the wastegate-actuator. Therefore
the bigger the boost of the compressor the more the wastegate opens and
the less boost will be produced. But less boost means closing the wastegate
more and therefore more boost will be produced. To get more control for
opening and closing the wastegates, the 3000GT/Stealth are having a solenoid
valve that, activated by the ECU, releaves some of the boost out of the
hose that runs to the wastegate acuators. This circle regulates the boost
our car needs to go that fast. This is the basic functionality for
getting more boost.
This is the easiest and
cheapest modification to a Turbo-driven engine. For only a few $ you can
get about 20% more power out of your beast ! This section shows why it
works and also the danger of it !
From the previos section,
we know how a wastegate acts. Check out the picture below. At the y-pipe
from the intercoolers (the black plastic ellbow that goes into the throttle
body) a vacuum hose is attached right at the ellbow (marked red). This
hose is running to a hose distributor called H-connector. At this point,
the pressure is distributed to the front and rear wastegates as well to
a stock solenoid valve. This valve helps the stock system to increase boost
by releasing some of the pressure in this hose connection into the intake
part. This means, if the solenoid valve is open, pressure to the wastegate
actuators will be lowered and the wastegates stay closed or even will be
activated later. If the solenoid closes the valve the full pressure from
the y-pipe goes to the actuators and, if pressure becomes more than the
load of the actuators spring, the wastegate opens and therefore less boost
will be produced.
Now we know that the stock
system controls the wastegates somewhat consevative and the maximum boost
is about 8 to 12 psi maximum that can be achieved. But if you look at the
drawing there must become something in mind. What will happen if I drop
the pressure in the actuator lines compared to the pressure i nthe y-pipe
? You're right, the actuators will be activated later as boost rises. Therefore,
if we are able to release about 2 psi of boost, we are having an advantage
now of 2 psi and gained that amount of boost ! On our cars, this modification
is easy, ..... but dangerous as well : If the vacuum lines for the wastegate
would leak and stay at atmospheric level the wastegates would never open
and you're car would run like hell around 20-30psi. But this would not
last for long as it'll kill your engine for sure...
It can be done with the
help of a cheap aquarium valve that acts as a Bleeder Valve. In
my setup I did 2 years ago, I used a professional bleeder valve with a
locking screw. It's very good quality and withstand high temperatures.
Also it cannot readjust itselfs...
Here you see how this bleeder
valve MUST WORK ! The blue arrow should show the pressure in the line.
A part of it is then bleeded to nowhere (or just the ambient) to reduce
the overall pressure in the line. Note, with only this kind of bleeder
and at this position, the best performance can be achieved. This because
the stock solenoid still controls the boost by the solenoid valve. If you
do a differnt setup, then you'll always loose low-end power
Where do I place the bleeder valve?
First, check out the modified
picture below. Here you can see that the valve is just placed before the
stock solenoid valve. This because it's so easy to reach to and can be
removed within seconds :) Please note, that you have to locate the hose
comming up from the H-connector ! This is the right hose as the ones at
the stock solenoid could be exchanged.
Also note the aftermarket
boost meter we need! You must have it as the stock unit is inaccurate,
too slow and shows not enough on it's scale. A definite MUST for tuning
in your new system.
To connect the gauge simply
cut the line that comes from the upper part of the intake manifold in the
middle and use a T-piece to connect the additional hose that runs to the
meter. The hose can then go through the firewall (under the steering column)
in to the cabine.
Do this before you install
the bleeder valve and go for a run to see if your readings are fine and
you're not having any vacuum leak. With the stock setting you should see
about 6 - 10psi, depending on the year and health of your car.
Now locate the hose that
goes into the stock solenoid valve. If you have an additional hose just
pull it from the stock piece and plug it to the one side of the bleeder
valve. Now use another piece of hose, connect it to the other side of the
bleeder valve and plug the other end to the stock solenoid valve. Secure
both side of the bleeder valve with small clamp or wire ties. Voilà,
that's it. Finally check for any vacuum leak as this is the evil for any
Picture not yet available
How do I adjust the bleeder valve ?
First, close the valve as
much as possible and then just open it a little. Drive the car savely and
watch the boost meter. On our cars, the most boost will be produced in
3rd gear from 3500rpm till about 5700rpm. Of course it depends on your
mods, age and more. S just drive your car in 2nd, hammer it through this
band and go into 3rd around 5000rpm. Rpm will drop to about 4000rpms and
boost rises very quick. Always keep an eye on the gauge and do not exceed
any boost over 15psi. If your car makes less than 14psi open the valve
a little bit more and secure the screw. Do this again and again until you're
at 14psi peak. Of course close it more if you overboost !!
As the 1st generation where
limited to 8psi these cars will gain a lot ! My european 3000GT TT made
284hp stock and we peaked up to 352hp with just this mod. This was in winter
time and after we checked it again in summer time we got about 334hp. After
readjusting the valve we where back at around 345 horses.
The bleeder valve cannot
work like a boost controller. This because it's a passive thing and it
cannot toggle the valve to wave-up the boost or to limit it. Therefore
it was only a timely mod as I saved the money or just waited until the
boost controllers became reachable for my wallet. Read the next section
about the boost controller setup. I highly recommend a boost controller
against the bleeder valve !
boost controller setup in our cars
The following drawing shows
the turbo-system of the 3000GT/Stealth TwinTurbo cars with a typical boost-controller
attached. Of course, my drawing is not complete in all details but contains
the parts that are needed to understand how the system works.
Remember the described
stock solenoid valve ? It releaves some of the boost that goes to the wastegate
actuators and therefore keep them closed longer as they would if the the
boost at the actuators is the same like in the intake. Also remeber the
bleeder valve, with its help we kept the wastegates closed even longer.
But all this setups do not allow to control the wastegates optimally. So
the best thing is to add an intelligent Boost Controller to your cars turbo
As described earlier, less
pressure to the wastegate actuators that their springs load keeps the wastegates
closed. For this, the boost controllers are using their own valve to reduce
the pressure that goes to the actuators.
The picture shows the
typical setup. The source for the boost pressure is the hose connected
to the elbow of the intercooler Y-pipe that combines the two intercoller
pipes and goes into the Throttlebody. This hose is now connected directly
to the IN port of the solenoid valve of the BC. The OUT port of the box
will then be conntected to the front and rear wastegate actuators. Please
note, that no bleeder valve nor the stock solenoid valve is needed because
the BC does its job perfectly with its own valves. To keep the drawing
as realistic as possible, I left the H-connector in place and only capped
the one hose that went to the stock solenoid valve. Also the valves input
A big note : Always check
for any vaccum leak as this is the evil for all problems and never overboost