July 28, 2023

6L80, 6L90 300mm Heavy-Duty Converter Builds: Breaking Down the Basics

GM 6L80 and 6L90 transmissions are a hugely popular units found in a variety of vehicles, from gas pickup trucks to diesel fleet vehicles to Corvettes to hotrod Cadillacs. The stock-size, 300mm torque converter is a critical weak point, and Sonnax multi-plate performance converter kits for the JMBX, JMBV, JMDZ and JMDY coded units make it easy to maximize reliability for the ultimate heavy-duty build.

Know Your Build: Performance vs. Heavy-Duty6L80 Converter Front Covers​​​​​​​

Performance: A 6L80/90 “performance” build typically means changing to a smaller diameter converter for a higher stall speed (ex. dropping from a stock-size 300mm to 265 or 258mm).

Heavy Duty: An upgraded 6L80/90 300mm converter is better described as a “heavy-duty” build because there’s no change in size for a higher stall speed. You’re just swapping key OE components for much stronger, more durable parts.

Sonnax offers top-quality converter upgrades for both performance and heavy-duty 6L80, 6L90 applications. Search this chart for the converter kit that fits your needs.

JMBX 300mm Build Options

The front cover and piston components in the JMBX performance converter kit also are available separately, giving you the option of good/better/best heavy-duty builds for the 300mm converter. Drivers looking to improve vehicle reliability should talk to a torque converter builder or performance specialist about speccing out a build.

Good (Basic Heavy Duty Build)

Forged Front Cover GM-CC-13

Front Cover GM-CC-13

Better (Extra Heavy Duty Build)

Forged Front Cover GM-CC-13 + Forged Piston Plate GM-DA-17P

Front Cover GM-CC-13 Piston Plate GM-DA-17P

Best (Max Heavy Duty Build)

Multi-Plate Performance Converter Kit GM-RK-21

Forged Front Cover + Multi-Plate Clutch with Woven Carbon Frictions + Forged Piston Plate

Front Cover GM-CC-13Multi-Plate ClutchPiston Plate GM-DA-17P

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While Sonnax makes every effort to ensure the accuracy of technical articles at time of publication, we assume no liability for inaccuracies or for information which may become outdated or obsolete over time.