I am trying to upgrade the turbocharger on my 2007 Volvo C30 T5 from the stock K04 to something larger and capable of supporting 350-400bhp.

I followed Garrett's website which allowed me to generate a spreadsheet of values, however I am running on several assumed values.

I have measured the manifold pressure of the stock turbo at ~16psig at full boost, and measured the current power to be ~250bhp (flywheel estimate from rundown measurement of drivetrain dynamic losses). The max RPM is 6500, displacement 153.8ci, peak torque at 3500rpm.

I have estimated the AFR (12:1), intake manifold temp (160F), HP per lb/min (9.9), BSFC (0.56/hr) and the engine volumetric efficiency (91%).

This has calculated a stock turbo pressure ratio of 1.98, with actual airflow at peak RPM of 28.11 lb/min, and at peak torque of 14.92 lb/min.

To support 350 bhp, I have calculated a pressure ratio of 2.70, actual airflow at max rpm of 39.20 lb/min and actual airflow at peak torque of 20.80 lb/min.

Does this seem reasonable? and what turbo can support this increase?

1 Answer 1


The Volvo T5 engine was used in many other applications such as the Ford Focus RS. I know that the RS turbo is capable of 400HP so you should look into that, maybe speak to a parts supplier to get a part number and price.

Another option would be the Garret GTX2860R which is often used with the T5 engine to produce 475hp

or the GT2867R which is good for 550hp

or the GTX3071R which is good for 650hp

  • Hi Terry, thanks for the reply. I have considered the Focus RS's K16 turbo, but I'd like to run an external wastegate with a screamer pipe, which I cant support with the K16 due to it being internally wastegated. I've just had a look at the Holset HX30 and HX35, plus the Garrett models you listed. Where I am struggling is selecting the correct turbine size, compressor size, trim and A/R ratios. A tuning site sell the GT3071r-WG but it is internally wastegated!
    – MIL-SPEC
    Jun 14, 2018 at 6:55
  • I wouldn’t worry about the internal wastegate, it’s not uncommon to weld the wastegate shut and use an external one. It’s even done on quite a few small scale production models and turbo kits. Jun 14, 2018 at 6:58
  • That's an interesting idea. Not possible on the K16 as it has an integrated manifold, but I could use the GT3071r-WG, although it is very expensive. Have you ever fitted a Holset turbo?
    – MIL-SPEC
    Jun 14, 2018 at 7:18

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