Nasty business: your WRX,
Air Power System's 33 percent power up kit and STi III performance &
dash; for under three grand!
There's a road not far out on
Melbourne, in the southernmost foothills of the Great Dividing Range, I call
Targa Victoria. Generally well surfaced with testing camber changes and mossy
shaded bits, there are superb increasing radius switch backs sprinkled generously
between 100 metre sprints. Cut into the side of a range, there's no room for
error on either side, but on a clear, quiet day, it's God's gift to motoring.
I've enjoyed it from the cockpits
of a highly capable arsenal over the years, mostly the hypo two wheeled variety.
But with the exhaust temp gauge showing 750 degrees C as we idle into the
60km/h zone on the other side, I struggle to think of another vehicle capable
of traversing this piece of bitumen any faster.
Hours earlier, in turbo-perfect conditions on Caller's drag strip, this APS-modified Rex ripped off half a dozen sub-13.5 second quarter mile passes. The fastest car ever recorded by our Correvit pulled one g in acceleration off the line, reached 100km/h in 5.0 sec dead and hit 400 meters in a sizzling 13.44, quicker than a $300K F355 Ferrari. Off the shelf, Subaru's Impreza WRX is one quick motor vehicle. And with four wheel drive grip, it has cornering performance to match: a point and squirt pocket rocket that make the inexperienced seem talented.
But this here is no ordinary
WRX. Bolted to it is a matched, five part power up system that increases
the 2.0 litre DOHC four's effective turbocharging, cooling and engine management
performance to produce 206kW. That's a 33% power increase.
But can APS get this much more
out of something Subaru can't safely and reliably? The answer is yes, according
to APS boss, Peter Luxon, thanks to a combination of increased boost, additional
intake cooling and technological control over ignition timing and air/fuel
ratios via programmable engine management computer chips, such as his own
This interfaces with the car's
original ECU to meter air/fuel ratios and ignition timing throughout the
rev range, in this case every 100 rpm. With modern engine management and
EFI you can dial in X amount of ignition timing or Z air/fuel ratio at any
given rpm, something distributors and carburetors were unable to achieve.
Here's the rub. You get
a moulded plastic cold air induction duct which supplies a cold volume of
air to a higher flow replacement air cleaner element; a simple water injection
system which is fed from the wiper/washer reservoir (problem is it runs out
before the fuel does, and you get an after market one for wiper water); Pro
Chip computer; and a full, three inch mandrel bent exhaust system with catalyst,
2.5 inch muffler and resonator and four inch tail pipe.
APS also adjusts the WRX turbo's
actuator to increase maximum boost from its standard 0.95 bar (14 lb) to
1.2 bar (18 lb). Because a turbocharger is a supercharger that operates via
exhaust gases from the engine, lower back pressure in the lower exhaust allows
the turbo to spool up quicker and, using the increased intake volume and later
wastegate opening, build more boost.
The downside is that when you
compress air you raise its temperature. The higher the turbo pressure, the
higher the air charge temperature. So to allow the APS System's increased
boost a simple water injection system was developed, in conjunction with
the original intercooler. Air charge temperature is increased by the turbo's
increased boost. The intercooler lowers this by around 50 percent and, just
before it enters the engine, a fine mist of water on the throttle body area
brings it closer to optimum temperature.
Water injection makes the extra
turbo pressure possible, which in turn allows a greater amount of ignition
advance. The further you advance an engine's ignition timing before detonation,
the more power, response and fuel efficiency you can achieve at both part
and full throttle opening. The water ignition is boost controlled (working
only above 0.8 bar) and far more cost effective than the $1200-odd you'd pay
for a bigger intercooler. But that and variable water injection are on the
drawing board for Stage Two: a 300kW WRX·
But how does it all work on the
road? Luxon says that much effort was spent on meeting the EPA's 90dB limit,
hence the 2.5-inch muffler. Its plenty louder than a standard WRX at idle
and our APS-kitted version made a deep burble all the way to its 7000 rpm
rev-limiter, kind of a cross between a V8 and Kombi.
Dropping the clutch at the strip
with 4000-5000 revs on board seemed the best way to launch. The front wheels
would spin up more than the rears, but with so much grip they don't turn
for long and fewer revs would have had the engine bogging down.
Under 3000 rpm its more tractable
and responsive than a stock WRX and there's enough useable power to rev cleanly
from 1500 rpm in fifth, or around 60km/h. But above that is where the APS-kitted
WRX's enormous torque increase really shows. At full boost the acceleration
is neck-wrenching and riding the engine's tidal wave of torque anywhere beyond
3000 rpm is supremely rewarding.
There's far less turbo lag
than standard, but the two stroke like rush at full boost seems to accentuate
its turboed nature. Throttle response and power delivery may not quite be
V8-like down low, but the APS WRX makes up for it with an unrivaled adrenaline
rush once it's on the boil. There's no question it has one-third more power
up top, but more suprising is the hop-up kit's extra punch where you need
it most. It feels like a bigger engine generally, with improved driveability
Will it last? Only time will
tell. We thrashed Luxon's car mercilessly for almost two days, and the only
problem we struck was the original clutch. "For 99 percent of consumers,
it'll be safe forever and a day because you just can't hold the vehicle at
ring-neck speeds for any length of time," he argues. "I'd say there'll be
a marginally shortened engine life through increased boost pressure, so ring
life may be three or four percent less than otherwise. There could be no
engine life reduction, or it could be as high as seven percent."
The APS System has passed both
ADR 30 (emission) and ADR 30.01 (noise) requirements, and its components
are covered by a 12-month/20,000km warranty. As with any after market modification,
you'll void your factory warranty and increase the already high insurance
premium. Warranty, insurance and durability questions aside, the APS kit
is professionally installed, inexpensive, user-friendly, almost maintenance
free and very effective. It makes your Impreza more than half a second quicker
than stock-as quick as the exotic, as yet unavailable Sti, in fact. The WRX
is a contender, but this is unquestionably the new Targa Victoria champ.