There are not many mods for the SC400.
You can do exhaust, headers, intake (with a full intake you HAVE to get an ECU upgrade, this is true even for GS400s), S-AFC, and torque converter. On a '93 I think the closest you could run is *maybe* mid 13's to high 13's at sea level... I'll be able to tell you for sure when I'm done
You can fit in a 150 shot nitrous kit and only need a larger fuel pump, that should put you into the mid 12's.
How much are you looking to spend? If I was to do it all over again I would have bought a '92 or '95 SC300 (5-speed) with messed up paint and bumpers with low miles. With the money saved I would buy a body kit, paint job, AFC and a Toyomoto 1.5 turbo kit (and debadge it, hehe). That's roughly 425 to the rear wheels on stock internals and pump gas. Mid 11's.
I can go more into detail, if you have any questions feel free to email me or PM me.
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