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 Pro Chip. 

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 to boot. 

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.