This is my first time here. But I just recently got a sc400 1992.

Just got this bad boy really at a great price. But it needed a new transmission and I saw that 1993 Toyota supra twin turbo automatic transmission will it bolt up to this. Is there any mods that i need to do extra. Also want to put the supra differential but want posi but want good free way mpg. Or should I just build a new posi unit for it. Please help.

The Supra twin turbo version of the A340E 4-speed automatic is the strongest one of all from the factory (same as all the other 1JZ-GTE and 2JZ-GTE A340E's). I believe it will bolt up(?) but you will have to look at getting a JZ-A340E bell-housing for it (should be very common to find used). There may be spline differences between the UZ and JZ versions of the A340 but I am unsure... maybe not? Others who work with those transmissions more will know.

That being the strongest A340 it's more often put behind turbocharged 1JZ and 2JZ engines with some extra trans oil coolers. The far more common version of the A340 that came from another SC400 might be better suited and cheaper... unless you've been planning for a big power upgrade and want to stay automatic.

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A 200mm LSD differential (Torsen T-1 type) from a Supra TT Automatic is what I assume you're referring to. If you can find one you can bolt it up once you have swapped on an SC style 101mm companion flange (propeller looking thing on the end) in place of the Supra's 111mm flange.

Those differentials have 3.769:1 gearing from the factory while your SC400 comes with an open diff 3.916:1 ratio from the factory so you will have very slightly less aggressive gearing but a little less fuel economy with the Torsen (barely a 1 MPG drop if that depending on how it's driven over a full tank).

Without more power than stock from your 1UZ-FE engine I don't recommend going with any rear diff gearing below a TT Auto's 3.76 or you will find that with, say, a 3.26:1 ratio while fuel economy will have improved the power-band and ability to accelerate will have decreased significantly. It's a different story with JZ or UZ engines pushing a lot of forced induction boost or with the 1998-2000 SC400's which used a 3.26 gear from the factory with a completely different automatic transmission.

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You can of course take your stock differential or any of the 200mm differentials with the SC style companion flange and rebuild them with any of the 2-way clutch-type LSDs on the market, any used 200mm Torsen T-1 or super-rare T-2, or OS Giken's sole 1.5-way LSD that fits these differentials. All of those LSDs have different properties that fit certain needs and usage scenarios better than others but they're all very good limited slip options.

Driftmotion sells a full rebuild, seal and bearing kit for our differentials minus the Toyota/Lexus-dealer-order-only factory side carrier shims that your driveline shop would be taking care of anyway if needed.

The original trans U1 30-40LE has a wired throttle cable the 30-40LS the a Electric Throttle (no cable) I have both trans & currently doing the swap but I came to a stop because of that