Doing the bolt-on and putting
APS's WRX Power Up claims to the test.
It quietly started a revolution:
Subaru's seemingly humble, giant-killing Liberty TS Turbo. Very few, around
1500 over four years, cottoned on to the sublime boxer-engined sedan. That
was until its little brother was released the Impreza WRX. A few more kW
and a lot lighter, the WRX has proved so popular over the years, everyone
wants a piece of the action.
From locally designed and manufactured
exhaust systems to Japanese produced blow off valves, boost controllers, intercoolers,
cold air induction systems and more, with so many performance upgrade options,
the claims of tuners and suppliers tend to get embellished at times, and
for the average punter it can be confusing.
APS High Output System for the Î97-â98 WRX claims it is able to produce 33 percent more grunt from a WRX, taking power from 155kW to 206kW.
As a quick brief, I have much experience
with standard and modified Libertys and WRXs, wrote the "What WoRX" technical
features a few issues back, have owned and modified two Liberty RSs and am
able to analyze products and claims with an open, independent and prejudice
Essentially, the kit consists
of four major components: a free flowing exhaust, cold air induction, computer
modification and a water injection kit.
The combination is the brain
child of Peter Luxon who, drawing on 18 years of off road 4WD Turbocharging
experience, turned his talents to Subaru's cult car.
Emphasis is place on delivering
the claims, reliability and low down response, with EPA testing a mandatory
To this end, APS spent many months
developing a computer program capable of "steering" a large percentage of
engine management systems. Four months of fine tuning a piggy back computer
control module resulted in APS being able to safely and precisely increase
the ECU-controlled boost on a â97 WRX from 13psi to 17.4psi, or 1.2
bar, through modified fuel and ignition maps. The VHS tape sized Pro Chip
case mounts on top of the standard harness through a number of wires and
alters the parameters full time.
Other developments included an
exhaust system that wouldn't foul the underbody, was neat, would meet EPA
noise limitations and yet provide excellent performance. A number of pipe
configurations and sizes were tried along with various catalytic converters
and something like 10 different mufflers. The '"inner" punches out a quiet
and legal spot-on 90dB and consists of 3" mandrel bent aluminised steel pipe,
a high flow catalytic converter, resonator and stainless steel muffler with
an off-set, perforated tube design. And for those who don't know, 90dB is
the maximum legal noise permitted by the EPA and, if ever pulled over by the
police, APS can supply the appropriate ADR37 emission and noise test report
documentation supporting its legality.
On the induction side, APS smartly
chose to retain the factory air box and use cold air induction to maximise
air flow without drawing in underbonnet heat.
Following the removal of the
factory resonating chambers mounted in the inner guard, a moulded polyethelene
one-piece ram tube mounts behind the driver's side brake duct and fits snugly
in the inner plastic guard. And to finish the air-induction, a flat-pad K&N
filter replaces the standard paper element.
The last part of the kit is the
water-injection. The kit is boost sensitive (adjustable, but generally above
12psi) and injects water from the factory washer bottle into the intake manifold
post-intercooler. Incorporating an anti-blow-back facility and electric pump,
boost is used to pressurize the water line to allow it to be injected into
the highly pressurized intake manifold. The kit includes a small bottle which
mounts in front of the battery, which is used as the windscreen washer reservoir.
The larger factory windscreen bottle's sole duty is now water injection. And
briefly, water injection sprays into the intake to suppress detonation and
cool the induction charge a little like a secondary intercooler.
Even fitted, the APS kit is difficult
to visually detect: the duct into the standard air box and the few lines
and wiring for the water injection are the only real clues.
Handed the keys and invited to
test its mule, at the end of the test drive the APS enhanced WRX came out
with the flag still at full mast and the test pilot impressed. Low-down and
mid-range response is, to put it mildly, sensational. Top-end though, because
of the relatively small turbo, does level off, but the kit is meant to enhance
what is already there. Up-changing at 6000rpm however, gave the most acceleration
and still managed a genuine push into the seat in lower gears.
Also impressive was a lack of
exhaust resonance or boom, particularly with the windows wound down. There
is a pleasant background burble, all within the 90dB limit.
The next phase was to put the
WRX through its paces in a number of 0-100km/h passes to confirm the seat-of-the-pants
With Peter Luxon behind the wheel,
with a hint of wheelspin and an ordinary 1st-2nd gearchange, it recorded
a "very average" 5.05 seconds. Second time, the launch was better and the
0-100 dropped to 4.76.
Third time lucky and tenths started
dropping: more wheelspin off the line improved the 0-100km/h to 4.62, before
a best of 4.50. I tried a few runs and reasonably easily managed a 4.78 and
4.66. I believe a perfect run would result in a 4.4 second 0-100km/h using
the G-Tech accelerometer. Quarter-mile times drop from the standard car's
14.3s @ 94mph, to 13.4 @ 103mph and could be (and actually was!) repeated
consistently at a Calder Park street drags meeting, and on a Correvit timer.
More importantly, from this power
output, we can calculate if APS's claim of 206kW is justifiable. And this
is where we get into a very delicate subject. Using the Sammut Drag Racing
Calculator results in a reading of 196kW, which in our opinion seems right
given the 206kW STi WRX runs a little faster 107mph terminal speed this being
the best indication of power. APS's Peter Luxon politely disagrees with this
figure suggesting from his vast previous dyno experience, and his time with
this WRX on a four wheel drive dyno, the APS kit does indeed produce its
claimed 206kW, and also rightly suggests all methods of calculating horsepower
are vague, unless the engine is run on an engine dynamometer. What also supports
his claim is that when testing both cars with a Correvit timer, the APS at
least matched the STi's acceleration times. Until we put them back to back,
we won't fully commit either way. Regardless, it is splitting hairs and the
point should be it far exceeds standard 155kW, can run mid 13's all day and
is fully legal, emission proven, and carries the full after-sales support
of APS. In terms of legality, it's the closest thing Australians can get
to owning the equivalent of an STi WRX.
A warranty is offered with the
kit and covers the components against manufacturing defects. The clutch,
for example, seems to stand up to the extra power with ease, but even APS
recommends if you're into regular drag racing, you may need to consider upgrading.
In the world of after market
performance parts, unrealistic claims are thrown about often. While certainly
not the only way of powering up a WRX, the APS kit comes as close to its
claims as you'd want, and is not only quiet and refined, but able to pass
any roadside emission and noise test. Power without compromise, that's what
we like to see.