40flash

I have just installed the ultimate semi-affordable Diff for a VQ or V8 conversion (in my opinion). It turned out to be much easier than I expected.
The gears that work for street driving with a turbo four are too low (high numerically) for a V8 or the VQ.
I am in the middle of an S14 VQ swap. My goal for the diff was two fold.
I wanted the 3.538 gear ratio that is found in the stock 350z diff. I also wanted a Helical diff. Here is how I achieved the goal.
I started with the pumpkin out of a 1996 Infiniti Q45. If you'd rather have the 3.7 ratio then start with the 97-01 Q45 which comes with the 3.7
Next step was to buy an S15 helical diff off Ebay. Be sure you get the output shafts with it. You will need them and it's usually cheaper that way.
Since the Q45 diff comes with the same 3.538 ring & pinion as the 350Z I didn't have to mess with the pinion gear at all which made the helical install very easy. Simply remove the output shafts (I used a rubber hammer) unbolt the old diff, remove the ring gear from it and bolt it onto the helical diff with the ring gear bolts from the Q45. (Use thread locker).
Bolt the helical assemby into the pumpkin being careful to put all the shims back in the same way they came out. Check the back lash to make sure it's within spec. With mine I had just a tiny bit too much slop (backlash). I made a new shim out of a beer can and put it in on the left side to get the ring gear just a few thousands closer to the pinion. That did it and it turned out perfect. Tap in the output shafts, fill with oil and put it in the car
Side benefit is that the Q45 diff comes with a speed sensor that can be useful to make your speedo work because the VQ trans doesnt have a speedo sensor like the stock trans did.
When doing an engine and trans swap you will need a new driveshaft. I would recomend Doing the rear end swap before making the driveshaft as the Q45 diff is a long nose diff which is about a half inch longer than the stock R200 diff and it uses a larger input flange.
This is a much easier swap than fabricating a 350Z into a 240sx and you end up with a helical diff instead of a Viscous diff with the same gear ratio. Hope this helps someone. John