Mating the turbine wheel to the turbine housing is crucial...
Too much space, and the exhaust gases just bypass the wheel.
Too little space, and you get contact.
The Hitachi HT-18 turbine wheel is not a standard Garrett wheel trim.
Basically, it's not going to work if you're trying to stuff a Garrett turbine housing onto the stock Hitachi CHRA.

Dude, I dunno why you're so stubborn on doing it this way...
Good, used S4 turbos (i.e.turbine housings) are almost a dime a dozen.
Getting a better replacement turbine housing is easy and cheap.

If you insist on a T4 turbine flange, why not just upgrade to a full T4 turbo?
Deals can be found on good, used T4 turbos all over the place.

I agree...I don't get it either.


-Ted

S4 and S5 turbine wheels are interchangeable according to Ted :)

Yep!

Let's see if we can eliminate the confusion...

Compressor wheels are identical.
Turbine wheels (and shaft) are identical.
Center housings are identical.
[The above all make up the CHRA (center housing and rotating assembly) - they are all identical.]
The compressor housings are identical.
The oil inlet / supply pipes are identical.
The water / coolant inlet / supply pipes are identical.
The water / coolant discharge / drain pipes are identical.

The turbine *housings* are different.
The oil discharge / drain pipes are different.
(Obviously, the turbo exhaust manifolds are different.)
The vacuum pipes on the S5 turbo compressor housing has a bleed for the boost control solenoid; the S4 turbo has no such thing - you can just plug this bleed, or remove (or bypass) the metal pipes and connect the vacuum fitting from the top of the compressor housing to the wastegate actuator.

Thus, to retrofit an S5 turbo onto an S4 13BT motor, you need to:
1) Use the S5 turbo exhaust manifold
2) Use the S5 turbo
3) Remove S5 turbo oil drain pipe and swap with an S4 oil drain pipe
4) Do something about the S5 boost control bleed

To convert an S4 turbo to use the S5 turbine housing + S5 turbo exhaust manifold onto your S4 13BT:
1) Use the S5 turbo exhaust manifold
2) Remove S4 turbine housing and swap in the S5 turbine housing
3) Loosen compressor housing and reclock to the proper position

Now, as I mentioned before, the Hitachi (HT-18) is based on Garrett turbo models.
All smaller internal parts are identical to Garrett T3 / T04 part, which include:
* carbon (compressor) seal
* Thrust bearing
* oil journal bearings x2
* snap-ring clips to retain above oil journal bearings x4, 2 per bearing
* turbine piston compression ring
This is why you can order a Garrett T3 / T04 "rebuild" kit to rebuild your Hitachi (HT-18) turbo.

The Hitachi HT-18 uses proprietary turbine and compressor wheels.
This means that the specs do not match any other (i.e. Garrett) turbine or compressor wheel specs.
This is why you cannot slap on a Garrett turbo housing onto the Hitachi HT-18 CHRA and expect everything to work.

Hope this helps!


-Ted

Thanks Ted, that cures up all the confusion I was having, sorry for the big redundancy trip. I'll keep my eyes open for a T3/T04 turbo to do the swapping/rebuild on as well as looking for better used turbine housings for the HT-18, see which one I come up with first.

Yeah you'll need to do that anyways because if you're turboing your N/A and you're using the N/A lower intake - the stock turbo and manifold won't fit.

I didn't have a stock turbo manifold to begin with.