from wikipedia
In May 1998 a NEO head was fitted, which enabled the engine to be classified as a low emission vehicle engine (LEV). The non-VCT and non-turbo was fitted to the R32 Skyline, the VCT turbo and non-turbo was fitted to R33 Skylines and the WC34 Stagea. R34 Skylines also use these engines, but they are fitted with a NEO head.