Best transmission for an LS swap

Match the transmission to your power, vehicle and budget:

Automatics

• 4L60E (common, compact): stock ≈300–360 lb-ft (≈300–400 hp); built units 450–500 hp.
• 4L80E: rated 440 lb-ft; the 4L85E 690 lb-ft. Heavy but strong; the boosted-truck favorite.
• 6L80/6L90: modern 6-speeds; the ratings in our sources conflict (being verified). They need a controller (GM ECU or Holley Terminator X Max + 558-499 kit).
• 8L90: 8-speed, GM rates it ≈900 Nm (≈664 lb-ft).
• ZF 8HP70: 8-speed, ≈700–750 Nm factory; needs an adapter and a standalone TCU.

Manuals

• T56 (F-body/GTO/CTS-V/Corvette): common swap choice; factory ratings range about 330–550 lb-ft across versions (F-body versions 350–450).
• Tremec TKX 5-speed: 600 lb-ft, slim for tunnel clearance.
• Tremec Magnum / Magnum-F / Magnum-XL 6-speed: 700 lb-ft.

Budget the controller (automatics), adapters, driveshaft and crossmember.