Ford 9in Ring and Pinion Lightened 666 Ratio

The Ford 9in Ring and Pinion Lightened 6.66 Ratio from PEM is engineered for enthusiasts and performance builders seeking superior acceleration and torque delivery in Ford 9-inch differentials. This precision gear set is purpose-built for street performance, drag racing, and aggressive off-road applications where quick spool-up and responsive throttle feel are non-negotiable. The 6.66 ratio sits in the sweet spot between highway cruising capability and hard-charging low-end power—ideal for forced-induction builds, turbo conversions, and supercharged platforms that demand aggressive final drive gearing without sacrificing drivability.

The lightened design reduces rotating mass within the differential assembly, lowering inertia and allowing faster acceleration response and improved launch characteristics. By cutting weight from the ring and pinion gears while maintaining PEM's exacting manufacturing tolerances, this gear set accelerates spool-up timing and reduces drivetrain lag—critical advantages in performance vehicles. The 6.66 ratio multiplies engine torque 6.66 times at the wheels, delivering stronger off-the-line punch and mid-range acceleration than taller ratios, while the precision-cut teeth ensure smooth, quiet mesh, minimal backlash, and extended service life even under high-load conditions. PEM's quality control and heat-treat specifications guarantee durability in boosted applications and repeated hard launches.

This ring and pinion set is best suited for Ford 9-inch equipped vehicles—Mustangs, Fairlanes, Rancheros, and custom hot rods—undergoing serious performance upgrades or racing preparation. Installation requires removal of the stock differential carrier, proper setup tools, and a working knowledge of backlash and preload adjustment; professional installation by an experienced differential technician is strongly recommended to ensure correct assembly and optimal performance. The 6.66 ratio works exceptionally well paired with overdrive transmissions or modern five- and six-speed gearboxes, allowing acceptable highway rpm while maintaining strong acceleration in all lower gears. Verify your vehicle's differential housing type and carrier compatibility before ordering.