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Go-Go GX

An Impreza GX wagon capable of 11s - and attracting prime-time media attention!

Words by Michael Knowling, Pix by Julian Edgar

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At a glance...

  • It started as a humble Impreza GX
  • Now it's a 280kW ATW monster!
  • On-screen star status
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It’s the days of traditional street machining all over again.

You may be old enough to remember when it was a ‘done thing’ for street machiners to buy a base-spec Torana, Falcon or Kingswood and proceed to drop in the gruntiest compatible motor. Gutless Starfire fours made way for 308s, 200ci Ford wheezers made way for Clevos and the Holden 202 made way for, well, almost anything.

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Well, here we are 25 years on and people are doing the same – ‘xcept this time around it's buying the most weak-knee'd late-model Subaru you can find and dropping in a compatible turbo motor outa Japan.

Jacob Cramp’s 1994 Subie Impreza GX is a perfect example. When Jacob purchased the vehicle about four years ago the previous owner had already performed a heart transplant – a Japanese-spec EJ20 turbo engine and driveline were bolted in. The conversion is a relatively straight-forward one with only a few minor changes needed.

Already having roughly 100 percent more power than stock, the only aftermarket power-up mods were a pod filter and custom 3-inch exhaust. A set of Liberty 16-inch wheels was also roped-in to replace the stockos.

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Jacob says the WRX-converted wagon didn’t go too badly. And, yes, he had driven something quicker than a Datsun 180B beforehand - a Silvia 1.8 turbo with a few bolt-ons. Unfortunately, this stage of development ended in a pretty nasty way – the Japanese-spec WRX computer is obviously tuned to run aggressive maps to suit Japanese 100 RON fuel and, well, running it on Australia’s lower octane fuel gave a predictable result.

One melted piston.

With a mortally wounded GX wagon sitting in his driveway, Jacob sourced a replacement motor from Rolin Imports and visited ChipTorque for a custom ECU program to suit. The custom program was tailored to maximise the performance to suit local fuel octane.

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A couple of other mods were also stirred in at this time.

A custom front-mount intercooler and a VF22 turbocharger set to deliver 15 psi boost gave the wagon a healthy 150kW at all fours. This was enough to keep Jacob happy for about a year.

But when a friend was forced to offload his 2.4 litre TRP-built EJ20 stroker motor, Jacob knew he couldn’t turn down the opportunity. After handing over a relatively modest amount of cash, he received a ready-to-go 2.4 litre bottom-end – all that was needed was final engine assembly. This task was handed to John French Performance, who finished the motor with standard ’94 EJ20 turbo heads and camshafts.

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A MicroTech plug-in ECU found its way onto the scene and works with a Bosch 044 fuel pump, surge tank and Sard pressure regulator. The standard coil-on-plug ignition set-up was also replaced with a set of four Bosch external coils and leads.

With only mild boost from the existing VF22 turbocharger, the car made 200kW at the treads and went on to record a fairly easy 12.4 second pass at the 2002 Jamboree.

“At that stage it had a Direct Clutch 3000lb heavy-duty clutch with only a standard gearbox so I was pretty gentle with it off the line,” says Jacob.

By now Jacob was severely addicted to his car.

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“I asked John French Performance which way to go to get more power – either rebuild the existing 2.4 or sell it and build a new motor using a factory 2.5 litre platform,” says Jacob.

In the end, it was decided to sell the 2.4 and purchase a 2.5 litre Liberty block equipped with ’98 WRX heads. The block was prep’d with sleeves, dowelling, ARP studs and a semi-closed deck conversion. The standard crankshaft was nitrided, teamed with billet rods and forged pistons. The ’98 heads were also given a port job, custom camshafts and heavier valve springs.

The turbo system also had to be upgraded to match the power potential.

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Jacob found a ZeroSports exhaust manifold and combined it with a custom up-pipe to mount a TurboSmart 45mm external wastegate and a HKS GT30/40 turbocharger (which was snapped up in excellent used condition for about half the new cost). A new 3-inch turbo-back exhaust was also fabricated to suit by Hinterland Exhausts. Jacob tells us the exhaust uses a US-sourced 4 inch cat converter that apparently causes zero restriction at any half-sane power output.

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A replacement bar-and-plate front-mount intercooler from Craig Dyson Rotary was crammed into the nose (with some bumper chopping required) and a TurboSmart Type 2 blow-off valve is fitted to the intercooler plumbing. You may notice something interesting in this pic – all of the vacuum lines lead into a shared vacuum reservoir below the strut brace. Jacob explains this gives a neater appearance, reduces the number of T-pieces and provides a better vacuum signal.

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A custom fuel rail set-up, braided SpeedPro fuel lines and monster 900cc injectors were also required to maintain suitable mixtures. Despite the massive injector capacity, Jacob says driveability is still very good. A MSD CDI unit proved difficult to interface with the existing remote coils so a ’98 WRX coil pack is now in service.

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More poking around in the engine bay will reveal a JR pod air filter, a Trust regulator-type boost control system, TRW fabricated coolant overflow tank, polished intake manifold and induction piping and silicone radiator hoses. Amazingly, the standard Impreza GX radiator – designed for a lowly SOHC 1.8 litre engine – remains up to the task of cooling this 2.5 litre beast.

With boost pressure from the HKS turbo set to 22 psi, Jacob’s wagon has clawed at the rollers of ChipTorque’s Dyno Dynamics chassis dyno to achieve an impressive 280kW. With some C16 in the tank and a few changes Jacob is confident of reaching his goal of 350kW at the wheels.

And what about the Subaru’s brittle AWD driveline?

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Well, Jacob toasted the previous clutch when the new motor was fired into life so a Jim Berry carbon 5 button clutch is now pressed up against the flywheel.

“It’s not the best thing to drive on the street but at least it doesn’t slip,” says Jacob.

There’s no way the standard gearbox was going to cop the bashing it would inevitably receive so Jacob opted for a Pfitzner ‘box with straight-cut dog gears from first to fourth gear and a standard Subaru fifth gear. Interestingly, 4.11 diff gears were fitted to the car when Jacob bought it but he’s since reverted to normal 3.9s. Why? Well, with the 4.11 gears the car needs to shift up to 5th gear momentarily down the quarter mile. With 3.9s he can hold it in fourth and save time.

Jacob hasn’t yet run the car down the quarter but expects it to run a low 11 as-is. A 10 second pass with C16 is almost a definite.

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From the outside, there’s not much to suggest this level of performance – an advantage of the street machiner’s drop-in engine approach. The paint is standard Subaru silver, a WRX bonnet has been bolted on and 19 inch DTM alloys roll under the guards. The ride height has also been brought down thanks to Whiteline/Drummond adjustable coil-overs. A Whiteline adjustable 22mm rear swaybar and a Japanese-import front strut brace completes the handling upgrade. The brakes are standard ’94 WRX – Jacob is currently looking for an aftermarket upgrade that will fit behind his 16 inch wheels that will be used for the drags. If he can’t find anything to suit he’ll probably settle on a ‘99/’00 WRX brake upgrade.

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Onboard, the trim is standard Impreza GX but a Japanese WRX dashboard has been wired in. Jacob has also added a MicroTech digital dash display and a boost gauge on the steering column. A basic Sony MP3/CD head unit takes care of tunes but Jacob admits there’s not much to be heard over the external wastegate, exhaust, pod filter, fuel pump, etc...

Jacob tells us – despite its mild appearance – his Subie wagon is well known around the Gold Coast.

Prime-time media exposure will do that.

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What’s the story, you ask? Well, one night Jacob was out driving and came upon a group of hot cars on the side of the road and a couple of cars that looked like they were about to pair-off. Sure enough, both drivers hit the load pedal – and so did Jacob! Coming up from behind, his silver wagon roared past both of the hotted-up cars in the break-down lane!

It later turns out that somebody was filming the event – a reporter for the current-affairs program, Today Tonight...

Granted, the footage may not have been used in the most complimentary light but you can’t buy exposure like that!


+61 7 5596 4204

Jacob would also like to thank Dyson Rotary for their assistance during the build-up.

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