If you remember the GZ, RZ and SZ, then the new Japanese spec trim levels on the A90 GR Supra will be familiar: RZ, SZ-R and SZ. Previously, the GZ was the full optioned version of the RZ twin turbo model while the SZ-R was the fully optioned version of the naturally aspirated 6 variant. With the A90 the RZ represents the 3 liter turbo 6 engine and the SZ-R and SZ carry the 2 liter turbo 4 motor. Without further details we would assume these engines would be some variant of the B58 and B48 power plants all coupled to the ZF 8HP automatic transmission.
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At the bottom of the page it also hints that the US market will only be getting the SZ, and the RZ and SZ-R trims will be exclusive to Japan. Here is the specification chart: