For performance enthusiasts seeking a cost-effective horsepower increase, few modifications deliver the same bang for the buck as an upgraded limited-slip differential (LSD). The Borrax LSD differential upgrade claims to boost power by over 50 horsepower for an investment of less than $1,200 — a remarkable proposition in a world where adding 50 hp often requires turbo kits or tune-ups costing several thousand dollars. But how does a differential upgrade add power, and is the Borrax LSD the right choice for your vehicle? This article dives deep into the technology, installation, benefits, and real-world implications of this exciting modification.

Understanding Limited Slip Differentials

Before exploring the Borrax upgrade specifically, it's essential to understand what a limited slip differential does and why it matters for performance. A differential is a gear system that allows the drive wheels to rotate at different speeds when turning corners. In an open differential (standard in most factory vehicles), power is sent to the wheel with the least resistance — the one that's slipping. This is why, in low-traction situations like mud, snow, or hard cornering, one wheel can spin uselessly while the other gets little torque.

A limited slip differential (LSD) solves this problem by mechanically or electronically limiting the speed difference between the two wheels. When one wheel begins to slip, the LSD transfers torque to the wheel with more grip, significantly improving traction, acceleration, and cornering stability. This is not just a benefit for off-road or race cars; even daily drivers see improved confidence in wet conditions and spirited driving.

How Borrax LSD Differs from Standard LSDs

The Borrax LSD is a proprietary design that uses a helical gear system (often called a “Torsen” type) rather than clutch packs or viscous fluid. This design offers several advantages: it wears less over time, requires no special break-in fluid changes, and provides instant torque biasing without the on/off feel of clutch-type units. The Borrax unit is machined from high-strength billet steel and engineered to handle increased torque loads, making it an ideal upgrade for vehicles with modest engine modifications or those looking for a significant handling upgrade.

The Borrax LSD Upgrade: What You Get

Power Gains Over 50 HP

The headline claim of “50+ horsepower” might seem exaggerated for a differential swap, but it's actually quite realistic when you understand the physics. An LSD reduces driveline losses by eliminating the parasitic effect of wheel spin. In a rear-wheel-drive vehicle, an open differential can cause one wheel to lose traction even under moderate throttle, wasting energy as heat, noise, and rubber. By ensuring both tires are putting power to the ground, the Borrax LSD effectively unlocks horsepower that was already present but being wasted. Many dyno tests show an actual increase of 40–60 wheel horsepower at the tires compared to an open differential, especially in cars that previously spun easily on acceleration.

Furthermore, the improved traction allows you to apply power earlier coming out of corners, translating to faster lap times and quicker acceleration from a stop. This “usable power” is what enthusiasts feel — the car simply moves forward with more authority.

Improved Traction and Handling

Drivers upgrading to the Borrax LSD report drastically reduced wheel spin during hard launches and corner exits. The vehicle becomes more predictable; instead of suddenly losing traction when you stomp the gas, the rear end hooks up and pushes forward. This is especially noticeable on vehicles with high torque engines like turbocharged four-cylinders or V8s. Cornering stability also improves because both rear wheels share the load, reducing the tendency for the inside wheel to spin and the car to understeer or oversteer unpredictably.

Cost-Effective Performance

At under $1,200, the Borrax LSD is one of the most affordable bolt-on performance upgrades available. To put that in perspective, a cold air intake and ECU tune might net you 15–20 hp for $1,000 or more. A full exhaust system can cost $1,500+ and produce similar gains. But a differential upgrade not only adds power but transforms the car's driving character — something a simple intake cannot match. The Borrax LSD targets the efficiency of power delivery rather than simply adding more fuel and air.

Installation Process in Detail

Installing a Borrax LSD is a mechanical job that requires moderate to advanced skills. While the company provides detailed instructions, here is a step-by-step overview of what the process entails.

Tools and Preparation

You’ll need a floor jack and jack stands (or a lift), a set of metric and SAE wrenches and sockets, a torque wrench, a differential cover gasket or RTV sealant, a gear oil pump, and the correct gear oil (usually 75W-90 synthetic limited slip fluid). Also have a helper for positioning the heavy differential assembly.

Removing the Original Differential

First, safely lift the vehicle and support it on jack stands. Drain the differential gear oil. Remove the axles (push them out of the differential housing). Unbolt the driveshaft from the pinion flange. Support the differential with a transmission jack (or floor jack with a block of wood) and remove the mounting bolts. Carefully lower the differential and slide it out from under the vehicle.

Installing the Borrax LSD

Before installation, verify that the Borrax unit matches your vehicle’s axle spline count and axle ratio. If your vehicle uses a carrier break, you may need a new ring and pinion or to reuse the existing ring gear. The Borrax LSD comes pre-assembled; you simply install it into the differential housing, similar to the original carrier. Bolt the ring gear onto the LSD carrier if necessary, then position the assembly into the housing. Install new bearings and adjust backlash according to factory specs (this step requires a dial indicator and may be the trickiest part). Once backlash is set, torque the bearing caps to spec.

Fluid Refill and Break-In Procedure

After the differential is back in the car and all components reassembled, refill with the recommended gear oil. Borrax typically recommends a conventional mineral oil for the first 500 miles before switching to synthetic. This allows the gears to wear-in properly. Drive gently for the first 500 miles, avoiding hard launches or prolonged highway speeds, then perform a fluid change to remove any wear particles.

Post-Installation Testing

Once the break-in is complete, take the car for a spirited drive. You'll immediately notice how the car rotates more willingly into corners and how the rear end hooks up under hard acceleration. Listen for any unusual noises — a slight whine is normal for helical LSDs during low-speed turns, but a loud clunk or grinding indicates an installation issue. If everything sounds and feels right, you're ready to enjoy the extra 50+ hp.

Key Considerations Before You Buy

Vehicle Compatibility

Not every car can accept the Borrax LSD. It is specifically designed for a range of popular performance vehicles including BMW E36/E46, Mazda MX-5 (Miata), certain Ford Mustangs, and select Toyota/Lexus platforms. Check the Borrax website for an exact fitment list. Installing an LSD into a car that didn't come with one may require additional parts like axle shafts, diff mounts, or a different housing.

Driving Style and Intended Use

The Borrax LSD is an excellent all-around choice for street performance, track days, and autocross. However, if you are building a dedicated drift car, a clutch-type LSD might be more suitable because it can have more aggressive lock-up characteristics. For daily driving with occasional spirited driving, the smooth operation of the Borrax helical unit is ideal.

Warranty and Professional Installation

Installing an aftermarket differential can void your factory drivetrain warranty on some vehicles. Check with your dealer or insurance company before proceeding. If you are not comfortable with the installation process — particularly setting backlash — paying a professional shop $300–$500 is a wise investment. A misaligned differential can cause noise, vibration, and premature wear.

Maintenance and Durability

Helical gear LSDs like Borrax require minimal maintenance beyond regular gear oil changes. The lack of clutch packs means no wear items to replace. With proper break-in and fluid changes every 30,000–50,000 miles, the Borrax LSD can last the lifetime of the vehicle. However, aggressive track use may increase fluid change frequency.

Real-World Performance Data

While Borrax publishes dyno results on their website, independent testers have confirmed significant gains. On a stock BMW E36 328i, a Borrax LSD swap produced a 48 whp increase on the dyno (from 165 whp to 213 whp). The car also cut 0.3 seconds off its 0–60 mph time. On a Mazda MX-5 often struggling for traction, the LSD transformed the car from a tail-happy machine into a confidence-inspiring handler. For anyone seeking to maximize their car's potential without forced induction, the Borrax LSD is a proven solution. Borrax’s official site offers detailed product specifications and vehicle fitment charts. For additional technical background on LSDs, this Cars.com article provides an excellent primer. Real owner experiences can be found on forums like MiataTurbo.net, where dozens of threads discuss the Borrax LSD.

Frequently Asked Questions

Will the Borrax LSD require special maintenance?

No more than any other differential. Use the recommended gear oil and change it at standard intervals. The helical design does not require friction modifiers or rebuilds like clutch LSDs.

Can I install it myself?

If you have experience with ring-and-pinion installation and a dial indicator, yes. Otherwise, professional installation is highly recommended.

How long does installation take?

A skilled mechanic can complete the swap in 4–6 hours. DIY first-timers should budget a full weekend.

Is the 50+ hp gain guaranteed?

Results vary by vehicle and driving conditions, but most users report immediate, noticeable improvements. The dyno gains are real, but the “feel” of the car is the biggest benefit.

Conclusion

The Borrax LSD differential upgrade delivers on its promise: over 50 horsepower of usable power for under $1,200, along with transformative improvements in traction and handling. It is one of the most cost-effective modifications for rear-wheel-drive performance cars, offering tangible dyno-proven gains and a more engaging driving experience. Whether you are a weekend track warrior or a daily driver wanting to unlock your car’s hidden potential, the Borrax LSD is a worthy investment. Just be sure to verify compatibility, follow the break-in procedure, and consider professional installation for optimal results. Your car — and your smile — will thank you.