that might be a very rare rb24s which indeed is a race engine (have a look at wikipedia - they have something about it, maybe?)
its a rb20 that had a gtr crank etc etc in it
the carbs meant that it could rev harder or something - and yeah it made like 300hp at some crazy rpm
taken from wikipedia:
This is a relatively unknown engine, as it was not produced for the Japanese domestic market. These were fitted to some left hand drive Nissan Cefiros exported from Japan new. Mechanically it is made from an RB30E head, RB25DE/DET block and RB20DE/DET crank with 34 mm height pistons. This engine used carburretors instead of the Nissan ECCS fuel injection system. This has the outcome of it being able to rev harder than the RB25DE/DET (as it has the same stroke as the RB20DE/DET) as well as being almost the same displacment as the RB25DE/DET. A common modification is to fit a twin cam head from other RB series motors while retaining the carburreted set-up. The standard single cam form produced 141 PS @ 5000 rpm and 20.1 kgf·m of torque @ 4,400 rpm.