Media Reviews 

"Power without compromise, that's what we like to see".  

Fast Fours and Rotaries Magazine  


by Patrick Felstead


After having owned and driven a MY99 Subaru Impreza WRX for 12 months, I decided it was time to modify. 

The standard WRX is a fantastic package, but I knew it was capable of more. I had experimented with my own minor modifications from time to time, but I wanted a complete powerup package with some real grunt, that had been developed for long term reliability, and that provided an engine warranty.  

Which Kit?  

I looked around Melbourne on and off for a few months, and decided on the APS Engineering (APS) Stage 1 kit. APS have their own 4WD dynamometer, an excellent reputation for forced induction modifications and complete system design, and over 20 years of experience in the after market industry.  

Since the WRX was first released a few years ago, I had read many favourable magazine reviews for the APS kits, and had been in a couple of APS kitted cars, so I was comfortable with the company and impressed with its product.  

The kit comes with a pro-rata engine warranty underwritten by a reputable international (Victorian based) insurance company, providing peace of mind in the event that something went wrong.  

Some may say that APS has a high profile due to their excellent marketing, but a decent marketing budget indicates a good research and development budget too.  

Initially, I wanted an ECU that I could adjust myself, but I soon realised when I had my variable bleed valve boost control, that I had it set to the highest level I could safely achieve most of the time anyway. Besides, how could a company provide an engine warranty on a kit if it was user adjustable?  

In the end, my decision was made based upon APSís reputation, their commitment to product development with their own vehicles, experienced in house tuning ability, the formal engine warranty, and the fact that the kit provided the power and torque gains that I was seeking.  

Customer Service 

I emailed the proprietor of APS (Peter Luxon) the "Bigger than Ben Hur" list of questions, and he rang me back the following day to answer them. On the phone, I confirmed with him what the kit consisted of, and the price. He told me that I would receive a discount for being in the Impreza WRX Club. After thinking it over for a few days, I decided to book the car in, and the following week, drove to the APS workshop in Bayswater, East of Melbourne, for the big moment.  

Peter re-confirmed what would be done to the car. He explained every part that would be fitted, and showed me some of the components that would be used. Later on that day, Peter rang and told me the car would be ready to pick up that afternoon. I was a little preoccupied for the rest of that afternoon as the anticipation was building! 

Kit Design and fit 

The Stage 1 kit consists of the following components:  

  • Unichip real time programmable Electronic Control Unit (ECU). This is a supplementary ECU that operates in conjunction with the factory ECU. Programming is achieved in real time, by plugging in a laptop computer to a connector mounted on the side of the Unichip.
  • Large twin entry top mount intercooler, with aluminium end tanks, tig welded and pressure tested. The factory intercooler hose is replaced with a nomex reinforced silicone rubber connecting hose.
  • Full 3" mandrel bent aluminised steel exhaust from turbocharger back, with a high flow 3" catalytic converter, and a high flow stainless steel muffler, with a dual 2.5" tips.
Peter also told me about a couple of optional extras that they could fit, which I also decided to go ahead with:  
  • Electronic Boost Controller module that is controlled via the Unichip, and incorporates an adjustable electronic fuel cut lifter/defender.
  • Cast aluminium cold air pipe with K&N cone filter mounted in the inner guard area.
APS has fitted many of these kits to WRXís and because of this, the installation is a quality job with no surprises. No holes are drilled in any metalwork. Attention to detail goes as far as either using the factory mounting points for all assemblies, or else, making up brackets to use the factory mounting holes (however, the turbocharger heat shield did require some rework to allow the 3" exhaust to mate to the turbocharger).  

In other words, the kit is almost "mass produced", ensuring a well practiced and polished installation.  

How Much?  

  • The cost (at time of writing) for the basic components is $3,500.
  • Installation, plus before and after dyno plot is $500.
  • The Unichip boost controller and high flow air cleaner add $700 to the damage.
Note that as I'm in the WRX Club, a discount was given on the $4,000 kit and installation price. Contact APS for a quotation.  

The Delivery 

It was a nice cool 21 degrees C the afternoon I picked the car up. It was about 6:30pm after Iíd finished reading and filling in the warranty paper work, and talking to Peter about the WRX in general, and the specific servicing requirements that I needed to perform in order to maintain the engine warranty.  

As I jumped into the car, I saw that the back seat had been folded down to make room for all the original parts, which were sitting on some bubble wrap. Bloody hell that OEM intercooler is tiny!  

I gently eased out of the APS workshop full of expectation, with the 3-inch exhaust burbling away in the background. I took it easy at first, getting used to the new and diverse range of aural qualities that my car had taken on. The exhaust note is fantastic, not too loud, but at the same time, letting me hear the flat four doing itís stuff. As the turbo spools up, the induction noise is quite audible through the K&N air filter. Whilst changing gears, the factory blow off valve could be heard slightly, followed by a really nice kind of a whistle from the air filter as the revs drop. You need to have a keen ear for this though.  

All of these sounds had been so confined and restrained before, but at a gentle pace around town, they are really quite nice to listen to, and unobtrusive. Thatís how a performance car should sound anyway; quiet during light load cruising, and during spirited moments, well, read onÖ  


All the peripheral factors such as customer service, kit design, reliability, fuel economy, etc. are important in making up the whole package, but performance is the bottom line that people look to in such a purchase.  

It was time to see what this beast could do.  

The first time I planted my foot, I said "Faaaar out", or words to that effect. A 2nd gear rolling start, you plant your foot and the G Force pushes you back into the seat hard, as the car rockets away. Itís hard to convey the feeling in words. As more and more air is sucked into turbo, the noise increases, and the exhaust barks. You literally ride a wave of torque and it keeps on building. At the top end of the rev range, the exhaust sounds like a swarm of angry wasps attacking, but itís always mellow. The rubber isolation bushes that the new exhaust sits on are performing their intended function nicely.  

If you want to impress your mates with your APS kit, put the Sube into 1st gear, give it about half throttle from the lights, and be prepared to see a silly grin from ear to ear on your mateís dial! Raw grunt is how Iíd sum it up. If you want to scare your mates with aggressive acceleration, give it about 4500 revs, and dump (or slip) the clutch. Donít try this with your Granny on board either Ė if the G force doesnít make her swallow her falsies, the noise will probably blow her hearing aid!  

To remove my biased and subjective perceptions, I borrowed a GTech performance meter from Dave Smith (thanks again Dave).  

With a full tank of fuel, and driver only, on an average 25 degree day, the car ran a 5.06sec for 0-100km/h, and 13.52sec for the 400m. This was the from the first run too. I didnít bother with any further attempts, as numbers arenít that important to me, and I know itís now a very quick car. Keep this in context of the standard car which (with a GTech meter again) took about 5.9 seconds to reach 100km/h from a standing start, and the 400m point in 14.1 seconds. Hey, that's quicker to 100 km/h than a standard 2 door Sti (on paper anyway), and about the same time for the standing 400 m. Motor Magazine's best times for the 2 door Sti are 5.38 sec, and 13.59 sec respectively.  

No doubt with less fuel, on a cooler day, and a couple more attempts at the launch, the car will probably achieve 5.00 seconds flat or less for the 0 to 100 km/h sprint. Oh, by the way, during the launch, I spun the wheels - I say spin and not chirp, because thatís what it was - which I've never done in a WRX before. Now if only I could have a bit of power oversteer every now and thenÖ  

The car keeps building power right up to redline, and doesnít taper off like the factory setup did just before 6000 rpm. Also worthy of note is that Iíve never heard the car ping since the kit was fitted. During the dyno tune, APS use a listening device to detect the onset of detonation, and the final tune includes a reasonable safety margin, to ensure the point of detonation is not reached under any conditions on the road or track.  

For those interested in peak power output figures, the standard car developed 90kW at the wheels, and the APS kit boosted this to a healthy 118kW, a power gain of approximately 31%. Not the highest figure APS can produce for a Stage 1 kit, but it all depends how the manufacturing tolerances stack up in your particular Rex. Tractive effort increased from 2400 Newtons, to around 3420 Newtons, a torque gain of approximately 43%. APS definitely know how to tune a turbocharged engine, especially the highly strung WRX.  

Without doubt, the car is brilliant all round. Maybe the top end power could be improved, but the Stage 1 kit has really been aimed at street use; Between the lights, or down a tight twisty road, it excels. However if youíre more interested in performing on a race track, you may be better off considering an APS Stage 2 kit that will provide even higher gains toward redline. For me, the car is brilliant as it is.  

On a final note for performance, in comparison to my own crude do it yourself method of achieving a higher turbo boost pressure, the power delivery of the kit is very smooth and progressive, and the car is much less jerky than it was with the bleed valve. Also, the car has been running on Shell Optimax 98RON fuel since early October 1999.  


The APS brochures and advertisements mention part throttle response and crisp acceleration so much, but itís all so true. In fact, the part throttle response and torque gains low down in the rev range are probably the most impressive features of the Stage 1 package.  

If youíre cruising along with the revs at about 2500 rpm in say 2nd or 3rd gear and you crack the throttle open, only a quarter or a third of the pedal travel, the car just takes off. The original Rex never felt like this. You need to be driving the car, and pressing the pedal, to get the full effect, but when it accelerates like that at only half throttle, itís a thrill.  

Off boost driveability has been improved too, by some clever tweaks in the right places of the Unichipís ignition timing map. Driving along on your average suburban street in 4th gear, and doing the part throttle thing again, results in strong off boost response. Itís a similar story even in 5th gear too.  

The dyno snapshot of boost pressure shows that by 2500 rpm, 13.8 psi of boost is being developed, and by 3000 rpm, it's on full song at a maximum of 16.5 psi. Note that on a cold day in 5th gear, max boost I've seen on my boost gauge is 17.5 psi. The boost controller then tapers this off in a linear manner to safe 14 psi (almost standard boost level) as the engine speed climbs to 6000 RPM and beyond.  

On the freeway, there have been a few occasions where I've had to look down at the gear lever to check that I really was in 5th! Even on warm days, the torque at speeds around 110km/h makes 5th feel like 4th. It really is impressive. This attribute of the tune really makes a difference in every day driving situations.  

Fuel Economy 

Power increases can be achieved by running an engine leaner (higher air to fuel ratio), up to a point, beyond which the cylinder heat becomes excessive leading to the onset of detonation or pinging. Subaru run the engine rich to help cool the cylinders and avoid detonation. They have taken the ultra conservative path, and deliberately run the engine much richer than is necessary, to cover themselves for vehicles used in all sorts of climates (read hot) all over the world.  

APS recognise this, and at light to moderate engine loads, they have had some scope to run the engine a little leaner than factory levels, in combination with ignition timing changes, to achieve that brilliant part throttle response. This is known as running in "closed loop" mode, which means that the oxygen sensor (mounted in the exhaust post turbo) measures the air fuel ratio, and feeds this back to the ECU so that it can add or subtract fuel in order to maintain the near perfect stichiometric level of 14.7:1 (lambda 1) air to fuel ratio.  

Above about half throttle (the mid load point in the fuel map) they do however run close to the richer factory air fuel ratios to maintain the cooling effect, as this is where higher boost pressure, and therefore higher temperatures, will be present.  

A desirable side effect of running a leaner fuel map in the low to mid load sites is that fuel efficiency is improved. Iíve proved that there are in fact fuel efficiency gains by keeping accurate fuel consumption figures, before and after the kit was fitted. Actually, Iíve done this for every tank of fuel since purchasing the car back in September 1998.  

I still need some longer term figures, but so far, after 12 tanks of fuel, my average fuel economy has dropped from about 11.5 L/100km, down to a miserly 10.5 L/100km. My drive to work is a 115km round trip, and the majority of it is freeway driving, so the figures are probably a little lower than most average city bound Rexes.  


The whole package has been engineered and refined by APS for power and reliability, and all the components have been designed as a complete package to work together. And work it does. The car feels like itís been released from a strangle hold imposed at the factory, making it a real joy to drive now. This is how the Subaru WRX always should have been.  

If you like your sound deadened European sedans, then maybe this kit is not for you. But if you want a lightning quick WRX that starts every time, that provides improved off boost characteristics, improved fuel economy, a fantastic exhaust note, and ballistic acceleration, all under the cover of an engine warranty, then I believe, you canít go past this excellent kit by APS. 

Many thanks to Patrick Felstead for his effort and his positive feedback. Patrick's web site is a wealth of information and well worth a visit.