I'm in the process of building a 400 to replace my tired old LG4 in my 85 Z28. I understand the the ECM controls the carb, distributor advance, and torque converter lockup. The new setup will have a Holley Carb and Vacuum Advance distibutor. Will the ECM still control torque converter lockup, or is another modification required? Also, with the engine swap comes a 10" torque converter, so how will that effect the mix?

 

The ECM will go into brain lock without the carb and distributor input, so - no, it will no longer lock up your TCC. You need a kit from Summit/Jegs.

The 400 is externally balanced, and such flexplates typically are 168 tooth rather than 153 tooth. Starter problems. Usually solved by a mini.

As long as the torque converter bolts to the flexplate and is matched to your engine (mostly the cam), it will be fine. 10" will probably stall pretty high, though.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).