Going from stock to 4:10, 4:30

[UZZ30-Québec]

MY friend has a stock MK3 supra turbo differential. (dunno if it's a 3.9 or 3.73)

What he told me is that if the internals of a MK3 supra Diff and LS400 diff are the same, he could build me a LSD differential for my LS400.

For my work, i bought a closed trailer 5X8' that I haul with my LS.

The problem is that I would like to change the stock 3.9 ratio for a 4.10 or 4.30 so the engine would rev a little more on highway cruises actually I drive with the trailer on the cruise @ 105km/h wich gives about 2100-2200RPM torque locked. Since the UZ doesn't have a lot of torque at these RPM I would like to make it rev a little more so the torque wouldn't lock/unlock/lock/unlock constantly, or downshift for nothing. Also the acceleration would be a little better and effortless for the engine but this point is really not a problem.

The real thing is when you haul it to a Tundra to really understand the difference in low torque between the 1UZ and 2UZ VVT-I. The 2UZ has a LOT more low-end torque. (and top end also! 325lbs/ft VS 260)

So, are the internals swappable? or is there a 4:10 or 4:30 diff I could fit on my LS400?. The LSD option is because Open diff with trailer in winter is not really cool. Open diff on stock LS sucks, i can't imagine with something to haul!. I know Non-turbo manual supras came with a 4:30 gear. 1JZ supra came with 4:10 gears, manuals are 3.9 and 3.73, automatics are 3.9. (i think all A34X-E diffs are 3.9)

 

[UZZ30-Québec]

Or is there any Higher gear that would fit there?

I'd like it to rev 2500-2600@ 105km/h. Maybe a little more.

 

[Blizzy]

The MKIII n/a Supra 5MT used a 4.3 gear ratio. It should be a direct swap for your LS.

I am running a 4.27 rear end, from the SC300 a/t, in my SC400 (which I believe has the same four speed trans as you). It hits 3k on the freeway at ~73mph. For the rpm goal you are looking for, a similar ratio is going to do the trick.

The stock ratio in my SC400 was 3.92, and the 4.27 LSD swap alone netted ~0.4s better performance in 0-60 and 45-65 times. Given your stock ratio around 3.6, the 4.3 differential from the Supra n/a 5MT should get you at least ~0.5s better 0-60 as well as the revs you are looking for the highway.

Moral of the story: target the 5MT n/a differential from the MKIII Supra. I would try Supraforums classifieds. They are normally for sale for under $100. Some guys have even performed the LSD swap already.