The ECU is easily the most
important piece of the
performance puzzle when it comes
to increasing the power of a
Subaru Impreza STi or WRX
engine. A qualified ECU
programmer or performance
workshop can perform an ECU
remap as a part of the tuning
process.
Subaru fits the WRX with an
extremely sophisticated and
powerful Engine Control Unit
(ECU), pretty much from Version
VII and and onwards. The Subaru
ECU chip operates like any other
computer, taking information
from a wide variety of sensors,
processing the collected data,
and based on this, generates a
number of output functions.
It
is these output functions that
determine actual engine
operating parameters such as the
amount of fuel injected,
ignition advance and turbo boost
pressure to name but a few.
These are complex calculations,
with the input/process/output
routine repeating on a
continuous basis over and over
again. In addition the ECU
continually error checks the
validity of inputted data, and
its own internal calculations
compared against the actual operation
and performance of your Subaru in order to keep
the engine operating safely.
Memory
chips that can be erased and
reprogrammed on the fly
countless times have been used in wide variety of
electronic consumer goods for
years. The
attraction for vehicle
manufactures is obvious, an ECU
chip can be standardised for
use across a wide range of cars
with only a calibration data
change required. More
importantly, upgrades or
patches can be easily applied
throughout the life of the car
in response to possible engine
management or emissions issues.
In typical form, the aftermarket
has wasted no time latching onto
this feature, with companies
such as EcuTeK, Cobb and Techtom
exploiting this new found
functionality, marketing engine
calibration software of varying
sophistication. So much so,
craggy grease-stained blokey
type mechanics are no longer the
real horsepower heroes, as this
title has shifted across to
pointyheaded software
programmers. It is revenge of
the nerds, real-time and in your
car!
The evolutionary process of the
WRX engine management systems
can be described in four broad
steps, with the advent of flash
re-tuning of the OE ECU being
the defining factor. Flash
tuning is something of a
revolution in the aftermarket
performance industry, and is
discussed in more detail in the
Subaru Performance Handbook.
OE Subaru ECUs are divided into
the following:
Pre-flash The Version I-IV
ECU was very much the dark
ages when it came of performance
tuning. Early models could be
modified with the addition of a
plug-in ECU chip, but with limited
results.
Flash 99-00 first Subaru ECU
to allow commercially viable
flash re-tuning, in addition to
a sophisticated ECU generated
data stream, accessible via the
OBDII data port. Fuel and
ignition timing are calculated
by referencing grams per second
of air mass against RPM.
Flash 02 current generation
ECU, as fitted to Subaru WRX models and
the Australian spec Subaru STi. Supports
active variable camshaft system
(AVCS) but not drive by wire (DBW).
Uses a much more sophisticated
fuel and ignition calculation,
expressed in grams per cylinder
charge, determined by a
combination of mass air flow,
manifold pressure and throttle
position.
Flash 04 the very latest ECU
system used by Subaru,
continuing on with the control
architecture of Flash 02, with
the addition of key features
such as DBW throttle control and
CAN bus communication protocols.
Used by range topping Subaru XT
Forester and USDM Subaru STi variants
as well as the MY06 onwards
Impreza WRX and STi.
Liberty/Legacy GT models feature
double AVCS (both intake and
exhaust cam control).
In the past, even relatively
simple performance parts
exceeded the capacity of the OE
ECU, to the point of becoming
somewhat of a liability in terms
of power and reliability. The
advent of EcuTeK has changed
this, as now the OE ECU can be
sent back to school for some
elocution lessons. Seasoned
engine tuners that previously
have had no experience with
flash ECU tuning, can often be
heard to exclaim I see the
light over and over when using
EcuTeK for the first time. In
terms of sophistication and
functionality, none of the
aftermarket engine management
products currently available
come close to matching that of
the OE ECU.
Reprogramming the OE ECU is by
and far the best method for
correctly compensating for the
effects of mechanical tuning on
engine operation. It is simply
the quickest, easiest and safest
way to come up with a tune to
suit most modifications that are
ever likely to be performed.
Advantages of reprogramming the
OE ECU include;
No need for risky electronic
boost clamps, bleed valves,
add-on interceptors or boost
controllers that otherwise
dilute the functional simplicity
of the OE management system.
No modifications to wiring or
sensors are required,
eliminating the potential for
system failures caused by badly
cut or spliced wiring.
Repair and diagnosis of a
re-flashed ECU remains exactly
the same as before. System fault
tracing and diagnosis is
unchanged simplifying
maintenance operations,
especially in remote areas away
from specialist tuners.
All the inbuilt refinements of
the OE system are retained, such
as civilised hot and cold
starting, throttle response and
idle quality.
Tuning the engine does not
have to start from scratch, as
the process of optimising
performance starts with a set of
fuel and ignition maps that are
very good to start with.
Additionally, only areas of the
OE mapping that need to be
changed are adjusted, instead of
having to start from a clean
sheet of paper.
All adaptive functions of the
ECU are retained and can be
improved in their operation to
harmonise completely with
mechanical tuning modifications.
Closed loop to open loop fuel
control transition points are
adjusted to improve engine
durability and driveability.
Active ignition timing control
parameters are modified to
increase both engine power and
driveability. While reliability
is maintained by adjusting the
system to react more
appropriately in response to the
increased intensity at which a
modified engine will detonate
at.
Sophisticated safety features
built into the OE ECU are
maintained, such as sensor error
checking, boost and RPM
limiting. The ECU also has the
ability to dynamically intervene
in the event of detectable
problems, and as it is still in
full control of the boost
control system, it can command
boost reductions in an
attempt to protect the engine
from damage.
The adjustable parameters via
EcuTeK include:
Base ignition mapping, active
ignition parameters and
compensations for temperature
and pressures.
Base fuel mapping, closed loop
operational parameters and
compensations for temperature
and pressures.
Desired boost pressure,
overboost safety cut limit,
turbo dynamics (to suit
different turbos and exhaust
characteristics), minimum and
maximum wastegate duty cycles
and boost pressure based speed
limiting.
Engine idle speed.
Fuel injector scaling.
Air mass sensor input scaling.
And a whole lot more!
What does this mean? In the
hands of a skilled engine tuner,
substantial improvements to
power and driveability are
easily within reach without
sacrificing any of good features
that set the OE ECU apart from
anything else available in the
aftermarket. Power gains of up
to 20kW can be made on otherwise
un-modified late model WRX with
a simple ECU reflash. When
combined with parts such as an
exhaust and intake, power
increases of 40kW and more can
be made over standard. In
practice there seems to be
really no effective power level
at which the OE ECU cannot
achieve, although it takes a
very skilled operator and a lot
more than just a passing
familiarity with EcuTeK to
extract really big power
outputs.
If you want to enhance
your Subaru, be it a mild set of
modifications or by going the
whole nine yards I recommend
that you factor in tuning
with EcuTek and understanding how the ECU
works is vital to getting top
performance from your car.
Find out lots more great
information just like this in
the Subaru Performance Handbook. |
