- Rototest Research Institute

Tuning theory, Part 3
RRI
The intercooler’s to be or not to be?
Is it really necessary to change the intercooler (or charge air
cooler) only because you want to charge a little more? There
isn’t exactly a lot of space in the front. RRI mounts a larger
cooler and analyses the results. And how do you actually
estimate the cooling ability?
BY GUNNAR LJUNGSTEDT, BILSPORT (TEXT & PHOTO)
Rototest Research Institute (TESTS, FACTS & GRAPHS)
Bilsport March 2006 (In English September 2008) • www.rri.se
Tuning theory, Part 3
Tuning theory, Part 3/5 2006
Imprint:
Tuning theory, Part 3/5 March 2006
•
This article is prior published in the Swedish car magazine BILSPORT nr 6, 2006
Text and photo by Gunnar Ljungstedt
Publisher:
Förlags AB Albinsson & Sjöberg
Box 529
371 23 Karlskrona
www.bilsport.se
•
Vehicle tests, technical facts and graphs by Rototest Research Institute, www.rri.se
Originally published in Swedish
•
Stainless steel, sport exhaust system and new catalyser from Ferrita Sweden AB, www.ferrita.com
•
New intercooler from Setrab AB, www.setrab.com
•
Engine tuning calibration, Turbo Center Stockholm AB, Claus Aichberger, www.turbocenter.se
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Rototest Research Institute 2008, www.rri, translation of Bilsport article from 2006
© Copyrights Bilsport 2006 & Rototest Research Institute 2008
2/10
Bilsport March 2006 (In English September 2008) • www.rri.se
Tuning theory, Part 3
CHASSIS DYNAMOMETER. The dynamometer is bolted on to the drive wheel with an adapter plate directly on the bolt circle. One for each drive
wheel, so a 4WD car requires four machines and will hang entirely on the machines. Since the dynamometer supports the car’s weight, the
suspension can move and function as normal.
In the previous featured
aricle we changed the
exhaust system and the
catalyst in our Volkswagen
Passat 1.8T 2003, and
Rototest Research Institute’s
(RRI’s)
measurements
showed that there is now
room
for
further
modifications. This time we
take on the intercooler that
was like a restriction even
when the car was in its
original state.
The original intercooler is of
course a compromise. There
is very little room in the front
and the production cost must
be held down to a minimum.
Besides, the 150 HP Passat
was never produced as a
racehorse, so there was no
reason to oversize the cooler.
But now we want more
3/10
power. First of all it must be
clear what the intercooler is
good for, and to understand
that we must know about the
loads that the engine is
subjected
to,
both
mechanically and thermally.
Higher density
The design limits these loads
wich are connected to the
demand of desired lifetime.
Charge air cooling is a way
to reduce the load on a
supercharged engine. The
efficiency and the size are as
mentioned
above
a
compromise by the car
manufacturer, so therefore
there is a lot to do if one is
willing to invest a neat
amount of money.
Interesting
performance
characteristics
are
for
example
pressure
loss,
efficiency
and
cooling
capacity. Generally you want
the perassure loss to be kept
to a minimum. By rule of
thumb, says Jonny Färnlund,
our guide at RRI, a welldimensioned cooler should
not have more than 0.1 bar
pressure loss at any time of
operation.
The primary task of the
intercooler is to cool the air
after the turbo charger,
before it enters the engine.
This is to reduce the air
temperature and achieve a
larger margin to knocking.
This in turn creates room for
more charging pressure and
increase of power.
– The side effect of reducing
the
temperature
is
a
reduction
of
cylinder
pressure, Jonny points out.
Then you reduce the engine’s
mechanical stress.
Increases with the flow
How efficiently it cools the
air is calculated using
Formula 1. The efficiency is
influenced
by
the
surrounding air-velocity.
The size and location of the
intercooler also have an
impact on the amount of
power it is capable to cool
off. A small cooler, or a
location that restricts the
cooling flow, results in a
limitation of the cooling
ability. We calculate the
cooling power using Formula
2.
With a well-functioning
Bilsport March 2006 (In English September 2008) • www.rri.se
Tuning theory, Part 3
η
ܶ௜௡ − ܶ௖௢௢௟
ூ஼ ܶ௜௡ − ܶ௢௨௧
Formula 1
ܲ
Formula 2
஼௢௢௟
= ‫ܥ‬௣ ∙௠∙ ∆்
ሶ
ܶ௜௡ = temp in to the intercooler
ܶ௜௡ = temp out of the intercooler
ܶ௜௡ = temp of the cooling air
ܶ௜௡ = temp in to the intercooler
ܶ௜௡ = temp out of the intercooler
ܶ௜௡ = temp of the cooling air
intercooler, the cooled off
effect
should
increase
continiously with the air
mass flow untill it reaches
max flow.
The unwelcome consequence
here is that the heat we cool
away has been produced by
the expensive petrol we
cursed when we paid for it
with hard-earned money.
Accordingly,
we
flush
money straight down the
toilet.
Sometimes it's hard to be a
car driver.
Theory can be destroyed
If the engine has no problem
with
knocking,
the
intercooler
does
not
automatically render higher
power.
– Theory can easily be
destroyed in practice, Jonny
emphasizes. No theory is
worth anything unless you
give it practical space.
If you tune, good cooling
will distance you from the
risks
of
knocking.
Sometimes you hear that a
larger volume in the intake
part, which includes the
intercooler, should have a
negative influence on the
throttle response in the
engine. This is true, but in
practice
there
is
no
noticeable difference.
If we take into account that a
fast engine easily swallows a
couple of hundred litres of
air per second, a volume
difference in the system of
4/10
COLLECTOR. There is a lot of data that has to be taken care of. Besides the parameters that are accounted
for in the articles series, large amounts of surplus data are collected. Can be useful on unexpected
occasions, so you can go back and analyze. RRI collects numbers.
range. However you might
see that the larger mass in a
big cooler still renders a
better initial cooling. On the
strip, the accumulated cold
of the material is used at the
start.
In the intercooler test, we
used a standard 400x302x45
Standard elements
mm aluminum intercooler
Due to the low mass flow at
element,
tanks
and
low revs, the profit of
connections from Setrab.
efficiant cooler will not be
Now we have changed
shown untill a bit up in the
some litres is not that
relevant any more. If we put
the cooler in the luggage
compartment, then we could
see a difference, but then it’s
a
question
of
quite
considerable volumes also.
exhaust
system
and
intercooler, and learned from
the results.
In the next featured aricle,
it’s time to investigate the
benefits of
mapping.
Remember that we run with
original turbo charger, air
mass meter and injectors,
which we found to be a
limitation already in the
original car. But maybe there
is still hope. []
“– Theory can easily be
destroyed in practice.”
Bilsport March 2006 (In English September 2008) • www.rri.se
Tuning theory, Part 3
accelerate by 500 rpm/s. We
discussed in the previous issue
why the torque looks different
As usual, the analysis of the than in the steady-state curve
RRI measurement results starts
with a glance upon the curves Perceived as gain
in Fig.1. Now we begin to have Jonny, who was certain that
enough curves to compare someone would give him a
with each other. The grey lines hard time about his statement
represent
the
standard that the volume of the
configuration; the blue lines intercooler not influencing the
were achiveved when a larger throttle response would not
exhaust system with race come true, now exhales. No
catalyst had been added, and deifference is seen inte the
the red curves were achieved trottle response.
with the current setup, having – Didn’t I say so?
added a more efficient The torque, on the other hand,
intercooler.
is decreced in the beginning.
But we still have not re- Why? The answer is probably
mapped the car!
that we have changed the
The torque curve looks a little hardware to such an extent
dubious. At one point, at 4000 that the information the
rpm, there is a torque peak. control system depends on,
The intercooler could not not is being interpreted
possible do this by it self. The properly anymore. Thus, we
reason the original map is not are getting to the point where
working is rather a question of the mapping becomes a
changed conditions. That does necessity.
not mean that there is a safety The torque bump at 4000 rpm
risk, but some intervention in also is a product of this. When
the control box would be of the car is driven with this
great value.
configuration it would be
Then we have a look at the perceived as stronger and
sweep in fig. 2, where the more alert because of this
engine has been made to ”defect”, just due to the
Measurements and
results
torque
having
been
outrageously low before.
– The human body is easily
deceived, says Jonny. Having
paid a lot of money it is even
easier deceived!
Double cooling capacity
But the intercooler was no bad
investment. It creates the
conditions for the continued
tuning. The reasong why we
don’t see a bigger difference in
Fig. 2 is that the pressure drop
over the original cooler was
reasonable good. However, it
would be surprising if the new
cooler would not be better
regarding it’s size. And as
expected, in Fig.3 and Fig.4 it’s
obvious that the new cooler is
far superior the old one
The biggest difference is the
cooling performance as seen in
(Fig. 2). The cooling flow from
the fan in front of the car is the
same
as
in
earlier
measurements, corresponding
approximately 80 km/h on the
highway, but the new cooler
gets rid of almost twice the
amount of heat compared tp
the old one, and has a good
efficiency. []
Conclusions
Exactly as in the case with the
exhaust system it can be said
that it is not possible to
consider only the change of the
intercooler. In any case not in
the actual case where the
pressure loss was small in the
original cooler. On the other
hand, the improved cooling
performance is needed when
we are about to increase the
boost.
Another reason can of course
be the right look, which is
important enough in some
circles. []
” The
human
body is
easily
deceived”
QUICK MOUNTING. The cooler that RRI tested was built from Setrab’s
standard parts. The tube connection has 50 mm dia. and the cooler
weighs 3.77 kg. The mounting looks a little weird but was made that
way for simplicity reasons. The cooler will fit inside the front, although
with some additional work.
5/10
Bilsport March 2006 (In English September 2008) • www.rri.se
Tuning theory, Part 3
Fig. 1
Power and Torque with big intercooler
It is obvious the ECU is having a hard time now. At 3000 rpm there is a decrease in power where as at 4000
rpm the increase is substantial.
6/10
Bilsport March 2006 (In English September 2008)
200 • www.rri.se
Tuning theory, Part 3
Fig. 2
Performance during acceleration
Same behaviour as with steady state tests. Less performance at low rpm with a big increase at 4000 rpm.
7/10
Bilsport March 2006 (In English September 2008)
200 • www.rri.se
Tuning theory, Part 3
Fig. 3
Pressure loss of intercooler
The standard intercooler has a low pressure loss and the new intercooler is just improving a bit.
8/10
Bilsport March 2006 (In English September 2008)
200 • www.rri.se
Tuning theory, Part 3
Fig. 4
Intercooler performance
The cooling performance is not very good on the original intercooler. The new one is good in this aspect.
9/10
Bilsport March 2006 (In English September 2008)
200 • www.rri.se
Tuning theory, Part 3
Chassis
dynamometer –
that’s how it works
To test the engine in an
engine dyno is both reliable
and repeatable, provided the
stand is properly calibrated.
But it is hard work and quite
expensive. The alternative is
often to drive on a rolling
road. Unfortunately, t’s not
very accurate. Friction losses
in the form of wheel slippage
increase with the power and
the
repeatability
is
questionable.
– Ordinary rolls are more a
loading method than a
measuring instrument, says
Jonny at Rototest.
The dyno RRI uses is a
ROTOTEST VPA-R chassis
dynamometer that is almost
painfully simple in its basics
but
considerably
more
advanced under the surface.
– After all, it was not that
easy to invent the wheel
either, Jonny counters. With
the
spreading
of
the
computers it was possible to
develop our system. The
simple part is the mechanics;
the electronics and software
are more advanced.
A tolerance of one percent
The principle is to bolt the
dynamometer directly on to
the car’s wheel hubs, via an
adapter. The car is supported
by the dyno units. The
suspension works normally
during the driving and there
is no tendency for the car to
break away. The force goes
into the floor instead.
The safety factor compared
to when using rollers with
cars howling, strapped down,
which want nothing rather
than drive right through the
wall, is not even comparable.
The
braking
power
is
10/10
generated hydraulically but
the measurement itself is
done separately.
– If you measured the oil
pressure, you would get a
hum, no more.
– The precision in the
rototest dynamometer, is like
in a very good engine dyno,
says Jonny. And it states a
tolerance within one percent
of measured value. Not many
test systems can match that.
Besides power and torque it
is possible to measure fuel
consumption, exhaust data
and other useful things in the
laboratory at RRI. Something
that car makers, tuning
companies and racing teams
all have understood and
profited from.
Different measuring
methods
Portable equipment is an
advantage. It’s only a matter
of taking apart the hydraulic
couplings and transport the
units
containing
oil.
Convinient, for example for
Shell, who have machinery
touring round the world to
present the new V-Power
gasoline. With custom made
software,
overtaking
is
simulated in front of the
audience.
Sound
hoods
covering the machines, make
them so quiet that the people
in the last row will hear the
knocking when the throttle is
hit and lower grade fuel
used.
Measurements
with
the
chassis dynamometer can be
done in two different ways.
The first is as a sweep over
the whole revs range, in
which
the
angular
acceleration (rpm/s) can be
determined (with the help of
the hydralics). The second is
steady state, in which the
engine is held at predetermined
load
points
The
formula
for
power
calculation?
Power (kW) = torque (Nm) x
revs (rpm) / 9549
The correction factor we get
by calculating (990 / air
1,2
pressure)
x
((inlet
0,6
temperature + 273) / 298)
The
correction
factor
multiplied
by
the
measured
Forget the 25 percent
value renders the normalized
losses
result.
In our series we always state 1 kW equals 1.36 metric HP or
the results at the drive 1.34 Imperial HP (often used in
wheels; because that’s the England and the US) []
power we can use to
accelerate the car. If you still
want to calculate the engine
power, it will be an
estimation, since we do not
know the exact losses in the
transmission. RRI usually
estimate seven to ten
percent loss in a manual
gearbox. Others will use
considerably more.
– If you take 200 HP, 20 of
these become heat in the
gear box, Jonny explains. It
cannot be much more before
the gearbox gets overheated.
Forget
figures
like
25
percent. Considering what
amount of heat that would
generate, you will quickly
realize that it gets quite hot.
Also the inlet temperature,
air temperature and air
pressure are measured for
the ISO correction. Normally
aspirated engines are usually
corrected to normal state in
order for measurements
made at different conditions
to be comparable.
– Generally, corrections are
reasonably right but never
exact, Jonny says. All engines
are more or less individual.
straight up to maximum revs.
The revs and the torque are
measured. Out of this, the
power is then calculated and
corrected to ISO standard
according to the air density.
The power is stated in kW or
HP at the drive wheels.
“Portable
equipment
is an
advantage”
Counting the horses
Normal conditions are an
airpressure of 990 mbar
when water partial pressure
deducted, and at 25 degrees
Celsius (298 grader Kelvin).
Bilsport March 2006 (In English September 2008) • www.rri.se