S400 Turbo Master Guide: S471/S472/S475/S480 Sizing, T4 vs T6, SX-E & Compound Setups

Building a street-strip truck, a tow rig that can breathe at altitude, or a competition setup that lives at high mass flow? This long-form guide breaks down the S400 turbo family—common compressor cuts (S471–S480+), T4 vs T6 housings, A/R selection, SX-E updates, compound pairing, and the fueling/cooling you need for reliable power on 5.9/6.7 Cummins, Duramax, and PowerStroke platforms.

Jump to: What Is an S400? • Popular Sizes (S471–S480) • SX-E vs. Classic AirWerks • T4 vs. T6 & A/R • Divided Manifolds & Pulse Energy • Singles: Street/Tow/Strip • Compounds: Matchups That Work • Fueling & Air Density • Install & Oil/Cooling Basics • Drive Pressure & What to Log • FAQs

What Is an S400—and Why Builders Love It

S400 is BorgWarner’s big single/atmospheric performance turbo “frame.” Think robust journal bearings, thick shafts, and wheel options sized to move serious air with durability. On diesel trucks, it’s common as a single in the 650–900 HP range, or as the atmospheric turbo in a compound set where a smaller charger handles low-RPM boost while the S400 supplies top-end flow.

Popular S400 Compressor Sizes & Where They Fit

Tip: “S4xx” naming focuses on compressor size; turbine wheel and housing A/R decide how quickly it lights and how much drive pressure you’ll carry.

SX-E vs. Classic AirWerks: What Changes

• Updated compressor aero (often billet, extended-tip): better surge margin and map width → more usable boost at lower shaft speed.
• Improved housings & porting: smoother flow, stronger castings.
• Still journal-bearing: keep fresh oil and correct drain angles; they live forever when fed clean, cool oil.

T4 vs. T6 & Picking A/R: Response vs. Backpressure

Footprint matters. A divided T4 turbine housing fits more easily and can feel lively with the right A/R (e.g., 1.00–1.10). T6 breathes more and is typically paired with larger wheels and A/R (e.g., 1.15–1.32+), cutting drive pressure at power but spooling slower.

Divided Manifolds, Pulse Energy & Why It Spools Better

A divided (twin-scroll) manifold feeds each turbine scroll with alternating exhaust pulses (e.g., 1-3-5 vs. 2-4-6 on inline-six). That pulse energy spins the turbine harder at low RPM, improving spool and throttle response without choking the top end when paired with the right A/R.

See BD’s heavy-duty divided manifolds for durability and pulse energy on popular platforms: Cummins T4 • Cummins T6 • 6.7L PowerStroke.

Singles: Street, Tow, and Strip Recipes

Compounds: Where S400s Shine

Compounds pair a smaller high-pressure turbo (fast-spooling) with a larger atmospheric S400. The small charger boosts into the big charger; total pressure ratio multiplies while each turbo operates in a happier part of its map.

Tip: Get the hot side right first (divided manifold, correct A/R), then size intercooler and piping to keep the air cool and pressure-drop low.

Fueling & Air Density: Don’t Starve the Charger

• Lift Pump & Filtration: High, stable supply pressure; quality filters; water separation. Starved rails → hot EGT and lazy spool.
• Injector/Rail: Sized for target HP; smooth commanded/actual rail track. On 6.7 PowerStroke, keep a sharp eye on fuel filters and water drains.
• Intercooler: Bigger core reduces shaft speed for the same boost—saves the turbo and cleans up smoke.
• Exhaust & Drive: Free-flow downpipe/exhaust; monitor drive pressure vs. boost (goal ≲1.5:1 under load).

Shop categories to support an S400 build: Lift Pumps • CP3 & Fuel • Intercoolers • Divided Manifolds.

Install Essentials: Oil, Drain, Leaks & Heat

1. Oil feed & drain: Clean oil, correct restrictor (if specified), and a straight, downhill drain—journal S400s hate aerated oil.
2. Boost-leak test: Pressure-test to 30–40 psi before first fire. Leaks make even the best S475 feel lazy.
3. Heat management: Wrap/coat hot-side where prudent; keep wiring and hoses away from the turbine.
4. Wastegate (if used): Set cracking by data, not guesswork. Aim to cap drive pressure under heavy load.
5. Bolt torque & v-bands: Follow specs; re-check after first heat cycles.

Drive Pressure, Shaft Speed & What to Log

• Drive vs. Boost: Target ≲1.5:1 at WOT; if 2:1+, consider more A/R, T6, or a gate.
• EGT Pre-Turbine: Controls durability; if it soars at part-throttle, find leaks or fix fueling/timing.
• Rail Commanded vs. Actual: Under-delivery = lazy spool and heat; fix supply/filtration first.
• Smoke Qualitative: Short puff acceptable; sustained haze means mismatch or leaks.

FAQs

What’s the best all-around S400 single?
A well-matched S475 on a divided T4 1.10 is a proven 700–850 HP street combo on inline-six diesels with the right fuel and converter. Heavier towing or higher HP often benefits from T6 1.15+.

Do I need a wastegate on an S400 single?
Not always. If drive pressure runs away (tight A/R + big wheel), a gate helps. In compounds, correct sizing and divided hot-side often keep drive in check without a gate.

Is SX-E worth it?
For many builds, yes—better map width and efficiency can lower EGT, reduce shaft speed, and widen the usable powerband.

Can I tow with an S475 single?
Yes—with the right A/R, converter, intercooler, and tuning. If you’re heavy/long grades, consider compounds for cooler EGT and altitude resilience.

Note: Build within emissions regulations. Many race-oriented configurations are not legal for highway use. Verify fitment and torque procedures in product instructions.