Daily Hillclimb STi

When this 2005 WRX STi originally came to us, it was for the installation and tuning of an engine management system. We soon realized that there were a few gremlins that the owner Paul thought were sorted. After powering up the ECU our crew soon realised that not only was the fuel delivery system not functioning correctly, it was not functioning safely. Obviously this is one part of the system you do not want failing, but more importantly there is no point of unsafe power.

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Apart from the near catastrophic work carried out by others on the fuel system, Paul’s STi is in fact a very strong build with immense potential. This potential is what we’re trying to extract with the use of correct parts, and correct installation carried out with attention to detail. Before we get into the custom exhaust and down-pipe fabrication, the spec list ;

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  • 2005 WRX STi
  • Deshele Performance built 2.5L EJ25 motor
  • Radium Fuel surge tank
  • Twin Walbro 450 pumps
  • Blouch DOM 3.5 Turbo with standard turbo positioning
  • Powertune custom oil breather
  • Powertune custom 4.inch exhaust
  • Process West V-mount radiator intercooler setup
  • Standard 6-Speed gearbox
  • Haltech Pro Plugin ECU
  • On E85 – 378.2KW on all four wheels @ 5,940rpm with a max 650Nm of torque being produced @ 5,190rpm
  • On 98 octane – 323.1KW on all four wheels @ 5,840rpm with a max 550Nm of torque being produced @ 5,420rpm

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With our efforts well underway in getting Paul’s vision back on track, and knowing the car has potential in creating big low end torque. We soon realised with the correct fuel delivery in place, we were in fact losing top end power from the high exhaust back pressure. Adam quickly got to fabricating a better flowing down-pipe and exhaust system.

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As you can see from the images, Adam is working in incredibly tight spaces when it comes to fabricating and fitting the down-pipe. The steering rack just so happens to be perfectly positioned to be in the way of our custom downpipe. One of the things Adam has to keep in mind is the removal and refit process, making sure there’s adequate room for clamps, v-bands, and mounts. Of Course for future servicing needs all these parts have to be easily removable, and relocatable. These factors greatly affect the design process Adam takes and very much shape the final down-pipe design.

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A thinner tube diameter would be the easy and obvious way out. But! We know the power benefits that we’re able to achieve with our chosen sizes, so to extract the full potential of the power base some fabrication ingenuity and persistence is required.  

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Adam uses an array of 304 Grade Stainless Steel tubes, rods, and bars. Brackets and mounts are taken care of with 12mm 304 Grade Stainless Rods and 25mm Bars. The exhaust itself is 4″ 304 Grade Stainless, Adam utilizing as many straight pieces as possible but where bends are needed a 304 Grade Stainless 4″ Flexi-joint is used. Pushing through and finishing it off with a Verex muffler.

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Achieving a quality exhaust system it all comes down to the final fitment. Every cut must be straight, and all the welds and joints must have perfect fitment to achieve a consistent and strong weld. The end result only depends on the attention to detail put into it from the very beginning.

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Once everything was pieced back together we got it on the AWD Dyno, and it produced a healthy 378.2KW at the wheels on E85 (323.1KW on 98 Octane). With the correct fuel delivery, fuel map, flow, and tune we’re very happy to say Paul’s project is back on track. It has great low end torque with 650Nm @ 5,190rpm. A very balanced chassis means this car is well suited to hill climb or Motorkhana styled events, but is just as comfortable being a daily street’er. We highly recommend a setup like this for people running 98 Octane, or where E85 may not be readily available. After spending some quality time with this WRX the most important modification we made was to repair the fuel system. With the whole system now operating safely for both driver and machine, the chance of catastrophic failure has now being eliminated. As you can see from this quick video below, Paul and his STi are now happily in tune!