The valve train is not serviceable outside the factory .... only the factory claims to have the setup equipment to assemble the VVEL cams (actually the camshaft and an eccentric shaft that varies the pivot point of the finger-follower to alter the lift as seen by the valve - or more correctly, the plunge depth that the valve "sees").
Since you cannot (in theory) therefore strip the head in order to polish the ports and ptentially reshape the combustion chamber, no-one has yet done a porting job on VVEL (HR-series) heads.
The Euro 370Z GT4 race engines are built using a 350Z block with stroker crank to 3.8 litres and DE series heads as they can be disassembled and modified. Even the Japanese Domestic sports car series is not using the HR heads.
RB
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