The Impreza WRX phenomenon shows no sign of slowing. Sure, the current models may be a little more contentious in terms of their prowess - not to mention styling - but with so many thousands of older models on the streets, the potential for kick-ass performance at a reasonable cost still remains. It's easy to become blasé - but we're talking constant four-wheel drive, an unflappable chassis and a helluva lot of turbo power.
And of course, it's easy to access a whole lot more of those kilowatts.
Here we'll watch the fitting of a basic power-up kit for the early Rexes - it comprises a new exhaust, under-intercooler replacement Y-piece, cold air intake and management modifications. Sold by ChipTorque as their starting power-up package, it's designed for mostly street use, perhaps with some club-level racing thrown in. Fitted, it costs AUD$3960, with distributors available worldwide.
The Baseline
The first stop for owner Mike Dawson's MY2000 (it's not at STi, despite the badging) was the four-wheel drive dyno at Dyno Source Queensland. The Dyno Dynamics design is the de facto Australian-standard, and the power readings were made in 3rd gear. (Therefore, absolute power figures should only be compared with other cars that have run on the same type of dyno in the same gear.)
Before putting the car through its paces, Lachlan Riddel of ChipTorque carried out a quick once-over of the vitals - oil and coolant levels, and a visual underbonnet check that nothing was astray. He also confirmed that the car had been fuelled with premium unleaded and then plugged in a laptop running the ECUTek Delta Dash software package that shows real-time engine management sensor outputs. While the car was being dyno'd, Lachlan wore earphones connected to a sensitive amplified microphone mounted on the engine - one of the best ways of detecting detonation.
Despite having a slightly dirty factory airfilter, the car pumped out a typical 112kW at all four wheels. This loss from the 160kW flywheel figure is typical of that achieved on this type of dyno on a four-wheel drive car.
The Exhaust
The exhaust used by ChipTorque in this kit is manufactured by Hinterland Performance Exhaust, also located on Australia's Gold Coast. Unlike many exhausts, the polished 3-inch stainless steel design is fully jig-mounted during construction, effectively assuring that every exhaust will fit like the prototype. The exhaust is available with either twin or single outlet mufflers, and comes with a single pipe off the turbo, a large cat converter, a braided flex joint, a small resonator and then the rear muffler. It is constructed of pre-formed mandrel bends TIG'd together.
But why only a single outlet off the turbo, rather than the more fashionable twin dumps, where the wastegate gets its own exhaust that rejoins the main pipe further downstream? Lachlan Riddel says that ChipTorque found boost surge with a twin dump design.
"When we tested the dual pipes we found that it was unnecessarily surgy," he says. "It also made a more annoying fluttering noise in the cabin when cruising on the highway."
Hinterland Exhaust's Todd Clark is proud of their exhausts and had some interesting points - which we'll cover in a moment - to make about aftermarket WRX exhausts.
To make sure that the turbine and wastegate flows can make their way smoothly into the dump pipe, John Hicks used an air die grinder to blend the flange into the pipe.
Because of its jigged construction, fitting the new exhaust is straightforward - just unbolt the old one and bolt-up the new. Important steps included the use of oxygen-sensor safe sealant on the turbo outlet flange...
...and anti-seize compound on both the oxy sensor thread and turbo flange nuts. "We might want to be able to get them off again one day," said Hinterland Exhaust's Kerry Haines.
The turbo heat shield needs to be modified to fit the big pipe. John marked out the cut....
...then used an oxy acetylene flame to make the new opening...
...before smoothing the cut with a belt sander. The raw steel was then painted silver to match the rest of the shield.
In this particular case the guys had run out of pre-built systems with single tip mufflers, so they custom fitted this single outlet design. Lachlan Riddel says that the single-outlet version is marginal in terms of legality - it's noisier that the twin outlet system. Once the muffler was fitted the pipe was polished, giving the same quality visual result as usual.
After a wipe-over with a special compound that maintains the polished stainless steel shine, the exhaust fitting was finished.
Some of the touches that the guys are proud of include adjustable hangers on the muffler, allowing the muffler to be precisely centred in the bumper opening before the lock nuts are tightened....
...and body clearances that are very tight on the leading edge of bends. The reason? As the exhaust gets hot it grows in length, so all these gaps open up. In running conditions, the clearances front and rear are fine.
Hinterland Exhausts also had a few interesting points to make about flex joins, recalling one aftermarket WRX exhaust that they had seen where the manufacturer had placed their flex joint in
front of the gearbox mount. Since the engine and 'box are bolted together, there's not a lot of point in having a flex there....
Finally, the guys made the point that all their hangers have stainless steel locating washers to prevent lateral movement of the system (the hanger is seen here mounted on the jig). A little thing, sure, but there's nothing worse than a knocking exhaust...
The Y-Piece
The intercooler - mounted above and behind the engine - needs to come off to allow access to the turbo heatshield and exhaust flange, so what better time to install the new intercooler Y-piece?
But what's all this about a Y-piece anyway? The standard Subaru intercooler entry is via a Y-branch made from small-diameter plastic pipe. The Y-junction (it's more like a 'T'!) looks quite poor in its flow capability and the convoluted tube bits are also a bit pedestrian. To add another nail to the coffin, the plastic piece has been known to split when working hard.
"We've seen a number of the plastic pipes fail over extended service, particularly for guys who do a bit of club racing," said Lachlan Riddel. "The plastic pipes simply overheat with the underbonnet temperatures and fail."
The replacement is this pictured cast alloy pipe, shown with the original. Which would you rather have?
The plastic pipe was removed, as was one of the original cast alloy elbows.
The Subaru elbow uses a gasket between the mounting face and the intercooler. Note the excellent match between the gasket and the opening. But unfortunately...
...the aftermarket new alloy Y-junction doesn't have quite the same quality of gasket match.
This mismatch was quickly overcome with some die-grinder work.
The new Y-piece in place. With the intercooler back on the car, this modification is effectively invisible - you can see it but you
really have to be looking.
With the exhaust now finished, the intercooler could be reinstalled.
The Intake
Back now at ChipTorque's workshop, it was time to have the cold air intake and the Xede interceptor fitted. ChipTorque head mechanic John Nash performed both jobs. First up was the intake - a quick and simple task. The new intake replaces the resonant box that normally hides in the guard (fender). It is made from moulded rubber tube, 3 inches in diameter. A single small diameter hole is drilled in the sidewall of the tube to reduce intake noise.
"Without the hole in the right place and of the right size they generate an intake whistle or scream at around 2800 or 2600 rpm," Lachlan Riddel said.
A short mild steel bellmouth is clamped into its opening. This aids the passage of air around the sharp lip that would otherwise be present.
The guard liner needs to be unclipped - it doesn't need to be completely taken off, just unclipped sufficiently to give access to the resonant box inside.
The resonant box looks like this. Unlike earlier Subaru turbos, in this design the intake air doesn't pass right through the box - instead the box is just tee'd into the intake. But what is the function of the box? Lachlan Riddel suggests that it is there to reduce noise.
"If you remove the resonance chamber on a car with a standard exhaust you will hear immediately why that resonant chamber is there!" he says.
Note that all the combustion air is normally drawn from the bottom-facing intake located under the bonnet. While some outside air can make its way around the headlight and into the opening, much air is inevitably drawn from within the engine bay. The new duct breathes all of its air from outside of the engine bay - together with the free-er flowing design, the lower temp air gives a performance improvement.
The upper end of the new duct pushes through the original opening into the airbox, while the lower end mounts behind the grille that already exists in the bumper/fascia.
The new duct in place, before the guard liner was replaced. Given that the bumper grille is actually fairly small in cross-sectional area, some holes in the base of the guard liner might not go astray...
The Xede
The Xede (pronounced 'exceed') is ChipTorque's own interceptor module - for more details on this device, go to "The Xede Interceptor". In this application it modifies the signals coming from the ECU, or going into the ECU, in order that timing, fuel and turbo boost can be varied from the factory parameters.
One mechanical mod needs to be made before a new boost range can be obtained. This involves replacing the restrictor 'pill' (which lives inside the factory boost control plumbing) with one having a smaller diameter hole. The factory pulse-width modulated boost control valve signal can then be modified to produce a higher boost level.
"Peak boost gets lifted to about 18 psi," said Lachlan Riddel. "Then we take that back to about fifteen at the top end - primarily for engine safety. But I'll see [on the dyno] what the engine's happy with - what sort of knock retard, what this particular car is like, whether it can stand a bit more boost pressure high."
"The primary advantage of altering boost with this method is that you have the inbuilt safety features of the standard computer. If it overheats, if it sees too much knock retard, it can turn the boost back to actuator pressure."
The engine management computer hides behind the passenger side floor in the WRX. It needs to be accessed so that...
...the new wiring can be crimped into place. Some Xede WRX installations are simple plug-in affairs, but in this case John used special crimp connections to make individual wire-to-wire connections.
With the nine wiring connections made, it was then just a case of plugging in the Xede and locating it next to the ECU back under the floor panel. Note that a bypass plug is included in the Xede loom.
Airfilter
Chiptorque sell a re-usable K&N filter element as part of the kit. However in this case the owner plumped for a new factory filter - a good move, we think. At only $40 for a genuine Subaru filter, it's cheap peace of mind re filtration, together with the normal excellent flow performance gained with factory paper filters.
Dyno Tuning
With all the bits of the kit fitted - a single day operation - it was time to head back to the dyno. The second dyno session had two functions: firstly, to allow tuning of the Xede for this specific car, and secondly so we could also see how many kilowatts had been gained. Same dyno, same day, similar temperature and humidity...
Again the ECUTek Delta Dash live datastream was used to monitor the car's sensors (including knock retard), while another laptop showed the Xede maps. Lachlan Riddel again used amplified earphones to detect any audible knock.
"We don't tune anything where we haven't got our own audible piezo-electric microphones on the engine," he said.
After a few minor problems (the Xede was initially configured for US market WRXs) the tuning could begin.
Firstly maps from another WRX fitted with the same mods were dumped into the Xede, then fine tuning for this car was carried out. Lachlan Riddel says that he adds 2 or 3 degrees of ignition timing on the transition into boost, something he says is needed on WRXs equipped with a high flow exhaust.
"By changing the exhaust system they end with a rich surge on transitional light boost," he says. "You can actually feel it quite noticeably on the highway at 100 kays if you haven't got the chip done correctly. It's surprising how much that small incremental change over that narrow rpm and load area makes a profound difference how the vehicle drives and runs."
In addition, timing is pulled out at the top end to allow for the high combustion pressures being experienced through the increased boost. Lachlan suggests that ignition timing of about 20 - 24 degrees is used at full load, high rpm. Finally, the boost curve is remapped and quite a lot of fuel is pulled out - an air/fuel ratio about 1.5 - 2 ratios leaner than standard is used at high loads.
Once the new maps had been finalised they were burnt into the Xede - should further mods be made, these maps can be easily revised to suit.
During the tuning process the power curve became smoother and fuller, until the results shown here were obtained. This graph shows 'before' and 'after' power curves and also boost levels. In standard form the WRX developed 112kW at the wheels, with the power peak from about 5600 - 6400 rpm. Maximum boost was 11 psi at about 3300 rpm.
In modified form peak power jumped to 145kW - a gain of 29 per cent. This was achieved with a peak boost reading of just over 18 psi; again this occurred at about 3300 rpm. The modified boost curve shows a linear decrease to 6300 rpm, where it has fallen to 14 psi. At revs higher than that it falls sharply, as does the standard boost curve.
Conclusion
Lachlan Riddel suggests that this kit is suitable for almost anyone looking to a first stage street enhancement. He says that it has good response on the track without having to change turbochargers, and doesn't unduly shorten the life of the clutch.
"It's a nice, easy to fit street kit that will respond well on the track in club applications, respond well on the street for nice driving, and it's still road legal," he says.
And what does he see as the downsides of the kit?
"I am sure there are people who complain that our kits cost more than they can do with a bleed valve or whatever but we pride ourselves on the quality of our work and the components in the kit."
But what did the man who had paid the dollars think? Well, first-up he wasn't too happy - on the road and track boost would just go away from no apparent reason. The problem was initially thought to be a defective boost control valve but even when that was replaced, the problem persisted. However, it was sorted by simply cleaning the electrical connections throughout the boost control system.
And now the owner is very positive.
"I am real happy with it," he said. "The only thing that annoys me is all the car club people telling me that it's going to wreck my motor, and the power's wrong, and it's too much boost - and all that!"
"But yes it runs very well - I am more than happy with the way it works. It doesn't do anything wild and comes on real strong down low compared with what it used to do, and it holds real solid all the way up past 6000 [rpm]."
"I would say that it's good value for money - like as far as the competition, anyway. You know everything's expensive when you have to pay for it, but if you look around and see what others are charging then I think that it's definitely a reasonable price."
"I'd highly recommend it."
Mike now has two more things on his wishlist - a surge tank to stop cornering fuel starvation and a water spray for the standard intercooler.
Contacts:
Dyno Source Queensland
+61 7 5596 7000
Hinterland Performance Exhaust
+61 7 5596 2338
ChipTorque
www.chiptorque.com.au
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