Danny, its the compressor wheel diameter not the trim which is different.

3076 = 76.2mm / 56 trim
3071 = 71.0mm / 56 trim

depending on which 3071 it is, there are also some potential differences on the exhaust side, some of them are a 56.5mm/90trim exhaust and some are 56.5mm/84trim, and others are the same as the 3076 at 60mm/84trim

The smaller exhaust ones will really struggle to break the 450bhp barrier, the 60mm/84 trim ones will do it relatively comfortably though on the right spec engine.


In terms of the difference on an engine, about 500-750rpm later spool typically and a little more laggy as well.

I personally think the 3076 is one of the best turbos around for most 2 litre engines, but on a standard YB the 3071 seems better suited for a road car generally as YB's tend to be relatively unresponsive for the same turbo than superior engines in this respect such as the vauxhall LET engine or Mitsi Evo engine, where bigger turbos seem to perform better in terms of response.
(mainly due to the stroke difference I should think)