Racing block for RX-Z is known as Y1. Y1 is very popular because it can withstand high temperature for long duration of usage. Also, Y1 has bigger displacement compared to Y2, Y3 and Y4. With Y1, you can also rebore the cylinder to get higher displacement without having to deal with overheating of the engine.
Original Japan Y1 block is very rare, since it has been replaced with the recent Y4. Anyone who wants to get Y1 maybe need to check for secondhand RX-Z.
The video here was found at YouTube, but there is nothing special to look at actually. I was hoping the uploader to show what he did with the block or tell us how to rebore the block.