The BorgWarner S300SX3 turbocharger has earned a strong reputation among diesel enthusiasts seeking substantial performance upgrades without breaking the bank. This turbocharger, part of BorgWarner's S300 series, is designed to deliver impressive power gains while maintaining reliable driveability. Understanding exactly how much power this turbo can add to your diesel engine—and what it takes to achieve those numbers—is essential before committing to the upgrade. This article breaks down the real-world gains, supporting modifications, and key considerations for installing the S300SX3 on common diesel platforms like the 5.9L and 6.7L Cummins.

What Is the BorgWarner S300SX3 Turbo?

The BorgWarner S300SX3 is part of the third-generation S300 family, which builds on the proven S300 platform with refinements aimed at higher flow capacity and better transient response. Unlike earlier S300 variants, the SX3 uses a larger 62mm compressor wheel paired with a 68mm turbine wheel, housed in a compact frame that fits many diesel engine bays without major modifications.

This turbocharger is engineered for medium-to-high horsepower applications. It uses a journal bearing system (with an optional upgrade to a ball-bearing center cartridge for faster spool) and features a cast-iron turbine housing that withstands high exhaust gas temperatures. The S300SX3 is commonly found in aftermarket upgrade kits for Dodge Ram trucks with 5.9L and 6.7L Cummins engines, but it also works well on Ford Power Stroke and GM Duramax platforms with the appropriate adapter.

Key Specifications and Design Highlights

Before discussing power numbers, it helps to understand the S300SX3's core specifications because they dictate where the power comes from in the RPM band:

  • Compressor Wheel: 62mm inducer / 79mm exducer, 7-blade billet design for high flow and efficiency
  • Turbine Wheel: 68mm inducer / 62mm exducer, 11-blade cast design with extended tip technology
  • Turbine Housing A/R: Available in 1.00 and 1.10 A/R (often the 1.00 A/R for quick spool on 5.9L, 1.10 for high-flow on 6.7L)
  • Boost Capability: Safely supports up to 40 psi; can be pushed to 45 psi with proper tuning
  • Bearing System: Standard journal bearing (upgradeable to dual ball bearing)
  • Flange: T4 divided inlet standard; T3 divided also available
  • Wastegate: Internal 44mm wastegate for simpler installation
  • Recommended Engine Displacement: 5.9L – 6.7L (also works on 7.3L Power Stroke but tuning differs)

The S300SX3 sits in a sweet spot: it provides significantly more airflow than the stock HE351 on a 6.7L Cummins while still spooling reasonably early, especially when paired with a good tuning file. The billet compressor wheel improves efficiency over cast wheels, reducing intake air temperatures at higher boost levels.

How Much Power Can You Expect?

The honest answer: the S300SX3 can add 100–200 horsepower and 200–400 lb-ft of torque to a diesel engine depending on configuration, but these numbers are not guaranteed out of the box. Real-world results vary widely based on engine health, supporting modifications, and the quality of the tune.

Typical Gains by Configuration

Here are representative dyno results from popular diesel forums and performance shops:

  • 5.9L Cummins (stock injectors, stock CP3, upgraded exhaust & intake): 480–520 HP / 900–950 lb-ft torque (up from ~325 HP stock)
  • 5.9L with 50% over injectors, FASS lift pump, and mild tune: 550–600 HP / 1100+ lb-ft
  • 6.7L Cummins (stock fuel system, DPF delete, custom tuning): 520–570 HP / 1000–1050 lb-ft (stock is ~350 HP)
  • 6.7L with upgraded CP3, large injectors, and 40+ psi: 650–700 HP / 1200+ lb-ft

It's important to note that torque gains are more dramatic than horsepower gains in many cases because the S300SX3 delivers a strong pull from 2500–3500 RPM. The boost curve rises quickly once the turbine hits its sweet spot (usually around 2200–2400 RPM on a 5.9L). Above 3500 RPM, the compressor can become slightly restrictive compared to larger turbos like the S364.5, but for daily-driven trucks that rarely exceed 3500 RPM, the S300SX3 is ideal.

Power Gains Without Supporting Mods

Installing the S300SX3 on an otherwise stock diesel engine will yield smaller gains—typically 50–100 HP—because the stock fuel system cannot deliver enough fuel to match the increased airflow. You will notice better throttle response and higher boost, but the engine will run lean if boost exceeds the fuel delivery capability. That's why the turbo is usually part of a complete performance package.

Factors That Affect Power Gains

Several variables determine whether you'll see the low end (100 HP) or high end (200 HP) of the S300SX3's potential:

Engine Condition and Age

A well-maintained engine with good compression and no excessive blow-by will respond better to increased boost. Older engines with worn piston rings or valve seals may not hold the higher cylinder pressures safely.

Altitude and Air Density

At higher elevations (above 5000 ft), turbochargers spool later due to thinner air. The S300SX3's compressor wheel can compensate somewhat, but expect 10–15% less peak power at altitude compared to sea level.

Fuel Quality

Low-cetane diesel or biodiesel blends can cause incomplete combustion, increasing exhaust gas temperatures (EGT). The turbo's turbine housing is designed for high heat, but sustained EGTs above 1500°F can damage the turbo and engine. Using premium diesel (cetane 45+) helps extract more power.

Supporting Modifications

This is the single biggest influence. The S300SX3 cannot reach its full potential without:

  • Free-flowing intake and exhaust (mandatory to reduce backpressure)
  • Upgraded fuel system (injectors and CP3 pump for 6.7L)
  • High-flow intercooler or air-to-water intercooler
  • Engine stability upgrades (head studs, valve springs)
  • Custom ECU tuning (no off-the-shelf tune will optimize it perfectly)

Tuning Quality

A bad tune can leave 50+ HP on the table, cause turbo surge, or push cylinder pressures dangerously high. A reputable diesel tuner will dial in fuel delivery, timing, and boost targets to match the S300SX3's flow map.

Supporting Modifications to Maximize Gains

If you want to cross the 500+ HP threshold reliably, these modifications are strongly recommended alongside the S300SX3:

  • Exhaust System: 4-inch downpipe and 5-inch exhaust to minimize backpressure. The stock exhaust on a 6.7L is choked at the DPF flange—remove the DPF and delete the EGR for best results.
  • Cold Air Intake: A S&B or AFE intake with a 4-inch inlet tube to reduce restriction ahead of the compressor.
  • Intercooler: The stock intercooler on 5.9L trucks is marginal above 450 HP. Upgrade to a Spearco or Fleece Performance unit with 3-inch inlet/outlet.
  • Fuel Injectors: For 5.9L, 50% over injectors are common. For 6.7L, 75–100% over injectors paired with an upgraded CP3 pump (from Fleece or Exergy) can support 650 HP.
  • Lift Pump: A FASS or AirDog system prevents cavitation and maintains fuel pressure at high demand.
  • Head Studs: Essential for any build over 500 HP. ARP 425 studs on Cummins engines prevent head gasket failure under high cylinder pressure.
  • Valve Springs: To prevent valve float at higher RPM (especially on 5.9L with 3500+ RPM tuning).

The order of importance: tune first, then fueling, then exhaust/intake, then head studs. The turbo is the centerpiece, but the rest of the system must support it.

Tuning Considerations

Custom tuning is non-negotiable with the S300SX3. A generic tune meant for a larger or smaller turbo will cause surge (chuffing) or excessive smoke. Here's what a good tuner will adjust:

  • Boost Targets: Typically 35–40 psi peak, tapering to 30–32 psi at high RPM to avoid over-speeding the turbine.
  • Fuel Delivery Ramp: The S300SX3 spools quickly, so fuel can be added earlier than with a stock turbo. Timing must be pulled slightly at peak torque to keep cylinder pressures safe.
  • EGT Management: At 550+ HP, EGTs climb quickly. The tuner will set a soft limit around 1300°F pre-turbine (limiting fuel) and a hard limit around 1450°F.
  • Smoke Control: The S300SX3 has enough air to keep smoke minimal if fueling is balanced. Expect a light haze at WOT; heavy black smoke indicates overfueling or wrong injector size.

Many diesel shops offer remote tuning via EFILive or HP Tuners. A base file can be sent after you provide engine specs, then adjusted via datalogging. Expect to pay $400–$800 for a custom tune.

Installation Overview

Installing the S300SX3 is a moderate DIY job for someone with basic mechanical skills. The process typically takes 6–10 hours. Key steps:

  1. Remove the factory turbo and exhaust manifold (on 6.7L, you will need to delete the VGT actuator and linkage).
  2. Install the new turbo pedestal or adapter plate if needed (the S300SX3 uses a T4 divided flange; most Cummins engines require a T4 adapter).
  3. Mount the turbo with new gaskets and torque the mounting nuts to spec (check oil drain flange alignment).
  4. Route oil supply and drain lines – the stock oil supply usually works, but you may need a -4 AN fitting for the S300. The drain requires a 1-inch ID hose.
  5. Install the wastegate actuator – the S300SX3 has an internal wastegate; set the preload to achieve 38 psi peak (adjustable via the rod).
  6. Connect the boost reference line to the wastegate canister.
  7. Reinstall intake and exhaust connections – you may need to modify the charge pipe to fit the 4-inch compressor outlet.
  8. Prime the turbo by unplugging the fuel pump relay and cranking for 30 seconds to circulate oil into the bearings.
  9. Start the engine and check for leaks. Monitor boost pressure and oil pressure closely on the first run.

One common pitfall is the oil drain location. If the drain angle is too shallow (< 45 degrees), oil can back up and push past the turbine seal, causing white smoke on startup. Use a flexible silicone drain hose and ensure it drops at least 1/2 inch per foot.

Reliability and Longevity

The BorgWarner S300SX3 is a durable turbocharger when properly maintained. Journal-bearing versions can last 80,000–100,000 miles under moderate use (daily driving with occasional towing). Ball-bearing upgrades extend life slightly and improve spool but are more expensive.

Key maintenance tips:

  • Use high-quality synthetic oil (5W-40 for most diesels) and change it every 5,000 miles maximum. Turbo bearings are sensitive to oil coking from overheated oil.
  • Let the engine idle for 30–60 seconds after a hard run to allow the turbine to cool and oil to circulate before shutdown. This prevents bearing fry.
  • Inspect the intake plumbing for debris or boost leaks regularly. A loose clamp can cause surge and overspeed the turbine.
  • Check wastegate operation annually – the spring can weaken over time, leading to lower peak boost.

With proper care, the S300SX3 can handle 600+ HP for tens of thousands of miles without issues. The most common failure point is the journal bearing if oil quality or changes are neglected.

Comparison with Other Turbo Options

The S300SX3 competes directly with other mid-range diesel turbos. Here's how it stacks up:

  • Vs. S364.5SX3: The S364.5 has a larger 64.5mm compressor, making 650+ HP easier but spooling later (around 2600 RPM vs 2200 RPM). The S300SX3 is better for a daily driver.
  • Vs. Garrett GTX3582R: The Garrett is a similar size but uses ball bearings standard, spooling slightly faster. However, it costs $400–$600 more and the S300SX3 has better aftermarket support for Cummins engines.
  • Vs. Stock HE351 (6.7L): The HE351 works well up to ~450 HP; beyond that, it becomes a restriction. The S300SX3 adds 100+ HP with better top-end flow and lower drive pressure.
  • Vs. Fleece Cheetah: Fleece Cheetah turbos are designed for high-horsepower racing (800+ HP) and cost significantly more. For a street truck, the S300SX3 is the better value.

For most diesel owners targeting the 450–600 HP range, the S300SX3 offers the best balance of cost ($1200–$1600 new), spool time, and power potential.

Conclusion

The BorgWarner S300SX3 turbocharger is a proven upgrade that can add 100 to 200 horsepower and 200 to 400 lb-ft of torque to a diesel engine when paired with appropriate supporting modifications and expert tuning. Its 62mm billet compressor wheel and compact T4 divided turbine housing make it a versatile choice for 5.9L and 6.7L Cummins engines, as well as other diesel platforms.

The key to achieving the higher end of those gains lies in the fuel system, intake/exhaust upgrades, and a custom tune that respects the turbo's characteristics. Real-world dyno tests from reputable shops (see examples from Fleece Performance or Exergy Performance) confirm that with 50% injectors and a proper tune, the S300SX3 can push a 5.9L Cummins past 580 HP and a 6.7L past 650 HP without sacrificing daily drivability.

If you're building a street-driven diesel that needs to tow occasionally, hit higher power levels for fun, and remain reliable for years, the S300SX3 is a well-documented choice. Study the BorgWarner official specs and consult with a trusted diesel performance shop to ensure your engine is ready for the upgrade. With careful planning, the S300SX3 will transform your diesel into a torque monster that still drives like a stock truck—until you put your foot down.