Torque Converters & Flexplates

Performance Torque Converters & Flexplates

The torque converter is the automatic transmission equivalent of a clutch — the fluid coupling that connects the engine to the transmission, allowing them to operate at different speeds during low-speed operation while locking up for direct power transfer at cruising speeds. Torque converter specification has a profound effect on how an automatic-transmission vehicle feels and performs: the stall speed determines where in the RPM range the converter begins to transmit significant torque, directly affecting launch performance and how well the converter complements the camshaft and engine tune.

With 185 products from Circle D, Hays, B&M, FTI Performance, and Quick Time, our torque converter range covers both performance street converters and purpose-built competition units for high-power applications.

Stall Speed Selection — Matching Converter to Camshaft

The stall speed of a torque converter should be selected to complement the camshaft's power band. A converter that stalls at 2,200 RPM paired with a camshaft that makes its power above 3,500 RPM will launch sluggishly — the engine is already past its torque peak before the converter has stalled and the car begins to accelerate. A correctly matched converter stalls at or slightly above the camshaft's torque peak, allowing the engine to build to its power band on the brake before release, and maintaining the engine in its optimal power range throughout the acceleration run.

Circle D Performance Converters

Circle D Specialties produces some of the finest torque converters available for high-performance street and strip applications — used widely in the LS performance community for their combination of high efficiency at cruise, consistent stall characteristics, and the durability required for repeated high-load use. Their converters are available in application-specific configurations for popular automatic transmission and engine combinations with stall speeds matched to common camshaft profiles.

Flexplates — SFI Certified and Standard

The flexplate connects the engine crankshaft to the torque converter, transmitting engine torque into the automatic transmission. Like the manual transmission flywheel, quality flexplates with correct ring gear tooth count and SFI certification where required provide reliable, safe service through the high rotational speeds and thermal loads of performance use. Correct flexplate selection must match the engine's balance specification — internally balanced or externally balanced — to ensure correct engine vibration characteristics.