IHI RHB31 VS Hitachi HT07-4A
Introduction
The IHI RHB31 VZ24 9402 is the OEM turbocharger on the Suzuki F6A DOHC and K6A. A popular upgrade is the Hitachi HT07-4A. The following picture is pretty popular on the internet, but usually the comparisons stop there.
Here we explore the differences and similarities between the two turbochargers in more detail.
Compressor wheel
On the left is the compressor wheel for the IHI RHB31 VZ24. On the right is the Hitachi HT07-4A. The IHI RHB31 VZ24 has 4 full-height blades and 4 reduced-height blades. The Hitachi HT07-4A has 5 full-height blades and 5 reduced-height blades.
The following table shows the dimensional differences between the compressor wheel for the IHI RHB31 VZ24, the RHB31FW used in the Suzuki/Monster sport F100 kit, and the Hitachi HT07-4A.
| compressor | IHI RHB31 VZ24 | IHI RHB31FW | Hitachi HT07-4A |
|---|---|---|---|
| major diameter | 36 | 40 | 46 |
| minor diameter | 25 | 30 | 30 |
| blade height | 13 | 16 | |
| tip height | 3.2 | 3.5 |
Turbine wheel
On the left is the turbine wheel for the IHI RHB31 VZ24. On the right is the Hitachi HT07-4A. Both have 9 blades.
| turbine | IHI RHB31 VZ24 | IHI RHB31FW | Hitachi HT07-4A |
|---|---|---|---|
| major diameter | 36 | 39 | 40 |
| minor diameter | 28 | 32 | 34 |
| blade height | 15 | 15 | |
| tip height | 3 | 5.5 |
Turbine housing
Again, on the left in this picture is the IHI RHB31 VZ24 turbine housing and on the right is the turbine housing for the Hitachi HT07-4A. The CHRA flange dimensions between the two housings are, surprisingly, identical. The HT07-4A is, of course, provisioned for the larger turbine wheel. It is also obviously of a different A/R than the RHB31. This can be seen in the size of the gap visible around the CHRA mounting flange and the size of the scroll visible through this gap.
Inlet and outlet flanges are the same dimensions between the housings.
Compressor housing
As can be seen in the first picture in this post, the Hitachi HT07-4A compressor housing is much larger in outside diameter than the IHI RHB31 VZ24.
The pictures below shows the EA11R compressor inlet gasket versus the inlet of the RHB31 VZ24 and HT07-4A compressor housings. The same gasket is used on the EA21R Cappuccino, as well.
It can be seen that the gasket is a close fit for the RHB31 VZ24, while being smaller in diameter compared to the HT07-4A. It is a paper gasket which can be trimmed to size. The inlet elbow should also be ported to match.
Conclusion
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