From what I have been able to gather so far, both the TO4R and TO4Z both use the same identical 84mm/66.7mm 63 trim compressor wheel, and 0.7 a/r compressor cover, so you are almost certainly correct Steve.
As sdminus says, where they seem to differ is that the TO4R uses the standard compressor cover, but the TO4Z has the antisurge vents, (exclusive to HKS) giving potentially a much wider flow range. Those vents would significantly change the shape of the compressor flow map, which may be why no flow map is published for the TO4Z ?? THe TO4R and TO4Z compressor wheels are considerably larger than the 62-1, 84mm versus 3" (76mm) outside, and 66.7mm versus 2.441" (62mm) inlet.
Another interesting feature of the TO4S, TO4R and TO4Z are that, although they have all the modern features of ball bearings and water cooling, and a modern efficient compressor wheel design, they all use the old school P trim turbine wheels.
That is probably why they call them a TO4, because that is exactly what the exhaust side is.
That may be good or bad depending on your point of view. But one advantage is that it opens up an absolutely vast range of alternative turbine housings. Single entry or split, T4 or T3 flange, tangental or central inlet, and A/Rs in at least eight steps from 0.5 to 1.71, and possibly more.
been answered before , yes Garret supply the core to HKS that use STD size exhaust/compressor wheels as fitted to a T04 garret Turbo., but the trick part of the TO4z is the TURBINE/COMPRESSOR housings are designed/developed by HKS.
Thanks Mark. I did try a search, but came up with no actual hard data or compressor maps.
From what I have been able to gather so far, the TO4r and TO4z both use the same identical Garrett wheels and ball bearing centre. The R uses a fairly ordinary 0.7 compressor housing, wheras the Z compressor housing has a few rather unique design features exclusive to HKS.