If the theory of evolution were applied to cars, you could take any vehicle, mix all of its components into a big box, shake vigorously for a million years and the end result would be something totally awesome. Well, hopefully !

The reality is, of course, that cars which evolve into the finest examples of their species require a mastermind to control everything.

Take this 96 model ‘Rex’ from the Xspeed import / tuning workshop in Perth, for example.

For five years now, Xspeed proprietor, Hanson Yeoh, has been slowly building his version of the ultimate WRX, testing, developing, tuning, tweaking .... and even styling.

You have to take a second look at Hanson’s weapon before realising that the chunky appearance isn’t actually standard.

The side skirts, wheel flares, front and rear bumpers are all custom items, designed and added to the car by an outfit called Fibrevision.

Apparently, those rear wheel arches have no less that thirty (yes 30 !) pieces, each joined and smoothed together. The car has also been jacked up on those arches, which must prove a point about how Fibrevision have bonded the bodywork to the car.

Since the car’s release in ‘94, the ability to work that flat-four engine into a 400hp monster has been a struggle and only a select few have dared to enter the forbidden zone and go inside the motor.

Admittedly, the WRX has for most been more than a potent package in stock trim and the term, ‘Best bang for your buck’ is well applied to the model.

For those who want a touch more excitement out of life however, please read on.

The starting point for Hanson’s beast was a closed deck STi RA block, chosen purely for its enhanced strength at high torque and horsepower levels.

Preparation of the RA block in this case was entrusted to the renowned Southside Engine Centre, who also re-bored the barrels by 10 thou’, so the capacity is now out from the original 1994cc to 2016cc.

Another operation performed by Southside was crank lightening.

No figures were provided on exactly how much weight was removed, but Hanson said that the webs were "machined back quite a bit"...

"The engine really does rev much freer with the lightened crank, and we’ve helped there too by adding an aluminium harmonic balancer that is half the weight of the standard one," explained Hanson.

It was, however, admitted that the lightened crank was at the expense of torque, but the loss of work effort was minimal.

Porting work in this case study centred mainly on the intake ports to allow more air into the engine.

After all, if you’re going to bolt up an AVO Garrett 400hp blower, you want what it produces to actually get somewhere, right?!

The turbo receives its exhaust gases via a match ported custom manifold and expels the waste through a Thermotec wrapped 3" mandrel dump pipe.

The remainder of the custom mandrel exhaust system is also 3" and ends with an HKS Super Drager muffler

Air for the combustion process meanwhile, is drawn in through a Blitz Sus air filter mounted on a Race Carbon Australia intake pod.

"We actually measured 880 cfm of air flow with the Blitz filter and the carbon pod," explained Hanson. "With a 3" pipe and no filter it was 920cfm, so we’re obviously very happy with it."

Air entering the engine is regulated by a 3mm oversize throttle body, but air flow in and out of the engine is also controlled to an extent by AVO cams.

These offer a maximum of 268 degrees of duration and 350 thou’ of lift, but it’s an area that Hanson is watching very closely indeed.

"The AVO cams were all you could get about 18 months back, but there could be a few other options coming onto the market really soon," explained the XSpeed head man.

"I’m presently investigating the possibility of STi version V cams, but Zero Sports and Jun in Japan are supposed to be releasing race spec’ WRX cams very soon."

Serious cams should be backed up by serious valve gear and in this motor the double valve springs and solid lifters are also from AVO.

The AVO ball bearing turbo in Hanson’s car is regulated to a maximum of 20psi and works with not one, but two, Apexi twin-chamber blow off valves.

"The dual blow-off valves are something we’re trying at the moment because there’s always a loss of pressure once the pressurised air is passed through the intercooler," said Hanson.

"We wanted improve turbo response when changing gears especially and find that, by placing one valve near the turbo and another near the throttle body, we are able to release more air out of the system and hence keep the turbo spooling. The system certainly seems to work when running higher boost pressures."

On the cooling side of the equation, a massive custom made air-to-air intercooler was made up by Grant at Per4Manz

It was decided to go for a longer intercooler with less rows to help cool the charge air better, while to minimise pressure loss, the core size has been kept down to 2 ½".

"So many people just try to wind the boost up with the WRX engine, without doing anything about fueling and engine management," said Hanson.

It’s alright to have a great big turbo on there, but if you haven’t got the fueling and management sorted, then it’s all a waste of time."

Fuel in this car is nothing but avgas, stored in the standard fuel tank but pumped by a Bosch high-volume / high-pressure pump and regulated by an FSE pressure regulator.

Ultimately, the gas is squirted by four STi 473cc injectors, positioned in the stock locations and fed by Earls 10mm ID braided lines.

The all important engine management meanwhile, is performed by Autronic’s SMC package.

Working entirely from map sensors and set up by Race Torque in Perth, the Autronic unit does away with air flow meters and O2 sensors (good for avgas !).

One interesting feature of the Autronic system is its rotational idling.

"It deliberately limits combustion at idle to just three cylinders, but ‘rotates’ this shutting down very quickly through all of the cylinders," said Hanson.

"The idea behind this is to aid cooling and it certainly works."

Now, if you’ve been reading thus far and are wondering what all this technological wonderment actually produces in real life figures, wonder no longer.

Hanson was extremely coy about quoting horsepower figures, for the simple fact that it would involve him in all the controversy that is presently raging in Western Australia as regards dynamometer readings.

When pushed, he said that the vehicle should be good for around 220kW at the wheels with 20psi of boost, as it has been dynoed at 202kw with 14psi at 6,000rpm.

Hanson added however; "The AVO turbo is absolutely great for bottom to mid range power and the response is great with virtually no lag.

"The only problem with this set up is that it peaks too early and I would really like peak power up around 7,000rpm to 7,500rpm. To this end I am considering a Turbonetics ball bearing T3 / T4 turbo ... either that or a similar turbo from HKS or Trust. Ultimately I want 280kW at the wheels, which is not entirely unrealistic."

Putting it to the ground
Playing around with power figures like this would quickly lead to the destruction of the standard WRX gearbox, but an STi Group A 5-speed cog swapper was a very early addition for this car.

With a 4.5Kg Toda Racing flywheel, 3500lbs pressure plate, 5-button brass clutch plate and 4.444 LSD diffs at either end, there’s already plenty of security under the floor too !

Nonetheless, the best can be made better…

"The STi box in there at the moment has a 1:1 fifth gear, which is really good for acceleration, but not top end," said Hanson.

"It’s not exactly perfect, but the version V STi Group A box is supposed to have a slightly taller fifth gear. The version V box is still a split case design, but it’s got additional re-inforcing which makes it stronger than all other previous Subaru gearboxes. There are an additional three mounting bolts to the engine as well, so that should minimise gearbox twisting."

Dealing with WRXs can obviously be very intricate indeed, and there are a few other things Hanson is considering in regards to the driveline. Cusco have just released a new centre diff’ called the Tarmac gear, which he has already ordered.

"It changes the torque split from 50 / 50 to 35% for the front and 65% for the rear, which should really improve the car’s punch out of corners," he said.

Equally serious is the suspension work performed on this Wrex and while we’ve already discussed much of it above, once again there’s a few future upgrades planned.

Here again though, things can only get better.

"There’s a set of STi four-spot front brakes and two-spot rear brakes sitting in the workshop waiting to go on, but we’re actually thinking of using either Brembo or AP Racing four-spots with the STi four-spots down the back," said Hanson.

And the interior of this wild WReX reflects what’s going on under all that bodywork.

There’s the usual array of custom gauges and electronic controllers, plus sundry re-trimming, carbon fibre and even a mild sound system.

Of course, evolution is an on-going process - even for the Subaru WRX species.

"The Aquamist will allow higher boost levels to be run due to the reduction in charge temperature," said Hanson.

"They’ve tested the same system on a Volvo S80 turbo and apparently it gained almost 30hp at the flywheel. We’ve also tried the Aquamist system on our WRX in Singapore and it’s so far proven to be as good as all the reports."

And the ultimate goal?

"Jun have managed to produce 480 horsepower at the flywheel from the WRX engine, but we’ll be happy with a genuine 400hp WRX that is reliable on the road as well as the drag strip and race track."

As the theory of evolution states - only the strongest shall survive. And this Tyrannosaurus WReX has the strength to do just that!

Nuts`n'Bolts