PRE Tuning

IHI VF40 and VF46 turbo comparison

IHI is the main supplier of OEM turbocharger to Subaru auto company. Although there are abundance of different turbo models across Subaru, they are mostly same turbochargers with slight variations. Today we will look at similarities and difference of the IHI RHF5H VF40 and IHI RHF5H VF46 turbochargers.

IHI VF40 is a turbocharger most commonly found in a Subaru Legacy GT, Forester 2.5XT, and Outback for the 2005-2007 model years.

IHI VF46 is a direct replacement for the VF40 on the 2008-2009 model year vehicles.

Similarities:

  • All internal components are the same. Both turbocharger use the same RHF5H rebuild kit: (journal bearings, clips, oil seals, retainers, fasteners, and thrust components)
  • Turbine housings are the same
  • Bearing housings are the same
Differences:
  • Compressor housings are different– Subaru claims to use a “new” 5 arc design which greatly improves flow and turbo response. Upon measurement of both housing the A/R ratio and internal volume seems to be very similar, thus this claim by Subaru seems to be more of an advertising gimmick than an actual engineering improvement.
  • Compressor wheels are different– inducer and exducer diameters are the same, total blade height and count is the same as well. Difference is in the height of the exducer blade tips. VF46 blades are slightly shorter, about 2mm. This prevent purchase of a VF40 CHRA and mating it with a VF46 compressor housing.
  • Wastegate actuator mounting is different– VF40 uses 3 of the 6 retaining bolts to clamp the actuator, while the VF46 uses only 2 of the 5 bolts to perform the same task. There is no advantage or disadvantage to either design. just noting a change.
  • Compressor seal plate is different– VF40 utilizes a smaller compressor seal plate than the VF46. VF40=119.36mm, VF46=130.07mm
Below you will find pictures of components compared:

3 Comments to IHI VF40 and VF46 turbo comparison

  1. james's Gravatar james
    21/12/2014 at 17:19

    can a ihi 46 fit on the 2005 legacy.


  2. Paul's Gravatar Paul
    25/07/2015 at 01:03

    I have a 2004 forester xt and recently purchased a vf46 to replace the blown turbo in my forester. I am extremely knew to Subaru but am a very talented mechanic. I already know it isn’t a exact replacement but will it work at all?


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