Rb/diff/speed question

[Kansei240sx]

Ok as a few of you know, i've got an S1 rb25det in my s13.

Here's my question, i've got a 91 and i've got a super hicas VLSD from another s13, now the gearing is really short for the RB's transmission, for instance, my rpms are really high compared to speed used to be with my KA . 3000 used to be just around 68-70 mph and now its more like 3700 for 70.

I've searched but havent gotten an answer, I've got a 300zx n/a VLSD, and the hicas one... is the only difference between these things the output shafts? Becuase i read the gearing is the same so swapping them out wont do anything at all in terms of changing it.

If so... Which diff should i get to help lengthen the gears? The J30 diff?

Also, are the output shafts swappable from the Z32 R200 to the S13 R200? Becuase i've got a open diff and a z diff and my friend wants it and i wanted to know if they're swapple without any problems.

PS: The RB25DET's transmission has 4.11:1 gearing. Thanks in return.

[naed240sx]

You want to use a lower gearing than 4.11:1 then. I believe that 3.6:1 was available in an infinity. Can't remember which though. Any r200 diff will fit.

[95lstegman]

get tires that with a larger section number. instant gearing change. NISMO used to sell lower rear gear ratios for R200's, but not any more. really what's wrong with 3700rpm at 70mph? i know my N/A SR transmission w/o stock rear end and tire sizes is 3000rpm at 60mph. it just means super spool on the highway.