Readers might be familiar with this beautiful Volkswagen Golf Mk5 R32. It came to us a couple of months ago for a custom stage 3 calibration for a Ruf supercharger kit that came with a pulley that produced 7.5psi of boost. With our custom calibration, it produced a healthy 203kw at the wheels from 123.5kw in naturally aspirated form.

Upgrade specifications

  • Stock engine
  • 98 RON fuel + AEM water injection kit
  • Upgraded injectors: Bosch EV14 550cc/min
  • Deatschwerks upgraded fuel pump
  • RUF supercharger kit + 11psi pulley
  • HPA charge cooler
  • Upgraded custom 2.5′ exhaust system with APR RSC muffler combo
  • Etuners custom Stage ECU remap for the RUF supercharger kit

The owner wanted more and acquired an upgraded pulley to produce 11psi of boost. He also upgraded the fuel pump and added an AEM water injection system to give a headroom for safety. Tuning this did not come easy as we encountered glitches during the calibration process.


Whilst doing a power run, the supercharger belt shredded into pieces. The exact root cause of it shredding is still a mystery as belt tension was reasonably snug, alignment appeared to be spot on and we did not hit the rev limiter. Upon closer inspection, it was noted that the pulley had some burr/sharp edges. After removing the burrs on the pulley, belt installed and we checked if the belt would show abnormal wear or not. After several short pulls, it was good to go.

We loaded an etuners custom file, tweaked the AEM water meth injection system very closely whilst observing AFRs and knock. It made a safe and healthy 233kw at the wheels. That’s a 30kw gain over the last setup with 7.5psi, and 109.5kw gain over when it was in naturally aspirated!

It is now a completely enhanced car with very linear powerband all the way to redline.

Performance results

  • Maximum wheel horsepower: 232.9 kW/317whp (measured 123.5kW as stock), gained 109.5 kW/149whp
  • Maximum wheel torque: 340 Nm (measured 210Nm as stock), gained 130Nm