Rex-perimental

You can just imagine what goes through someone’s mind when they pull up alongside James Stewart’s MY01 Subaru WRX. The pronounced flat-four beat makes it known there’s a big exhaust but other than that it looks standard; a quick car but easy prey for, say, an LS1 with ‘the usuals’.

And then the lights change.

It turns out you were wrong.

With 260kW at the hubs and the all-round torque of a 2.5 litre, this green Rex wagon is outa there at one hell of a pace.

James never intended to go whole-hog with a WRX and, truth be known, he wasn’t really hankering after a Rex when he bought one. James explains there was no Impreza RS available in Australia at the time so for decent performance you had no choice but to sign for a WRX.

And that he did.

Having stepped up from a Ford KA Laser, the ’01 Rex was a vast improvement – but it wasn’t as quick as expected. As you may remember, the ’01 WRX put on weight compared to the previous generation and didn't have the shorter gearing or variable cam timing found in later models.

James’ aftermarket development began after the rear muffler was damaged and it was cheaper to replace it with a high-flow MRT unit. Well, things kinda snow-balled from there and, a few visits later, the car had a full MRT 3 inch exhaust, MRT up-pipe, STi intercooler, IHI VF34 turbo and custom EcuTeK program. This yielded a fairly typical 195kW at the hubs but, still, the WRX was a bugger to shift off the mark. There wasn’t much below 3500 rpm.

About this time James had the opportunity to purchase a 2.5 litre EJ flat-four – the US-spec STi 2.5 litre short block. James decided to take the plunge and, much to his delight, MRT offered to use the car for 2.5 litre R&D purposes.

Fast-forward to the present and the engine has been out of the car five times and has trialled numerous bits an’ pieces. Brett from MRT tells us the standard US-spec 2.5 litre turbo (which is the same block as the local Forester XT turbo) has relatively delicate pistons that can give problems at boost pressures above 17 psi. As a result, James’ car runs MRT forged pistons in conjunction with custom rods. ARP studs and special head gaskets are also incorporated in the build.

The standard MY01 cylinder heads are seen as the worst for chasing power so MRT bolted on a pair of STi Version 6 items. A few different sets of camshafts have been tested and the current profiles provide an excellent torque spread. James says some monster cams were tested with the standard MY01 WRX heads but he wasn’t happy with the resulting driveability. There are no adjustable sprockets but there are GFB lightweight pulleys.

You may also notice the aluminium radiator. This wasn’t necessary to cope with the extra grunt of the engine – rather, it replaces the stock radiator which went ‘bang’.

The standard EJ exhaust manifolds connect to a MRT up-pipe and Garrett 400hp roller-bearing turbocharger. With boost pressures as high as 22 psi, a MRT/HyperFlow front-mount intercooler kit does a great job chilling charge-air. The intake to the turbocharger comprises a MRT cold air induction (with a filter mounted in the front right guard) and silicone hose kit. A GFB Stealth blow-off valve is also installed. The exhaust is the latest MRT version with a separate passage for the turbine and wastegate bypass.

During each stage of development, MRT tuned the vehicle using EcuTeK programming software. The current tune runs up to 22 psi of boost with relatively tame ignition timing and mixtures. Fuel is delivered through 800cc injectors teamed with a MRT rail set-up running twin regs. A 500hp Walbro pump shoves fuel to the engine bay.

At a maximum of 22 psi boost, James’ stock looking wagon has pushed out a healthy 260kW at the hubs of MRT’s Dynapack dyno. And there’s certainly more waiting to be released – we’re told that the standard MY01 intake manifold and exhaust manifolds are forming a power barrier. James says it starts to choke at about 5500 rpm.

“Above 2000 rpm you know something’s starting to happen, at 3000 it’s all happening and by 3500 rpm you’ve got 22 psi,” he says.

On the road, James says the 2.5 has more torque in all low speed operating ranges. However, the restriction caused by the stock intake and exhaust manifolds mean there’s no point approaching the 7000 rpm limiter. But, still, it’s a wider and more accessible ‘power band’ than anything Subaru has built...

The driveline has received a MRT strengthened clutch and lightened flywheel. The gearbox also runs MRT high-strength helical 1^st and 2^nd gears, which were fitted as a precaution. A gearbox bearing noise prompted the gearbox upgrade.

The chassis is improved with a Whiteline 22mm adjustable rear swaybar with Whiteline bushes. This improves overall balance but James says there’s considerable body roll – a set of aftermarket springs will soon be installed. The wagon body (which isn’t as rigid as the sedan) will also be beefed up with some bracing.

The brakes are also on the ‘to do’ list. Most likely is a set of DBA discs and a master cylinder brace. These yet-to-come suspension and brake mods will give James the opportunity to “get serious” with some circuit work.

James has gone for the stealth look for his R&D beast. The car is completely standard – rims an’ all. At the time of our photo shoot the polished aluminium front-mount intercooler was plain to see, but this has since been painted black.

Sneaky.

The interior trim is also stock aside from an EcuTeK dash monitor. This provides a wealth of engine data as well as some limited user-tune functions – you can lower boost, retard timing alter mixtures and more (For more info see http://www.autospeed.com/cms/A_2175/article.html)

From here James doesn’t plan to do much more to the car other than the suspension and brakes. But you never know what R&D opportunities might appear in the near future...

Contact:

MRT Performance                                              +61 2 9809 2110

                                                                        www.MRTrally.com.au