S400 Turbo for Cummins: 5.9L and 6.7L Sizing, Fitment & Kits

The Cummins inline-six is the most common home for an S400 turbo in the world. The 5.9L 12v and 24v and the 6.7L all respond well to a big single — strong bottom ends, plenty of displacement to spool a large frame, and a deep aftermarket for manifolds and fuel.

This guide covers which S400 size suits which Cummins, what changes between the 5.9 and the 6.7, and the fitment hardware you will need on top of the turbo itself. Black Sheep Industries machines that hardware in-house and builds the True North Turbos TNT4R 400-frame line in Canada.

Why Cummins Owners Go S400

The factory Holset on a 5.9 or 6.7 runs out of air long before the engine runs out of appetite. Once you are past roughly 600 wheel horsepower, the stock frame becomes the restriction — drive pressure climbs, EGTs climb with it, and you are pushing more exhaust past the wheel than it can use.

An S400 solves that by moving to a much larger compressor and turbine in a frame the Cummins has enough displacement to actually light. What you give up is low-end response, which is why sizing matters more than raw capability.

S400 Sizing by Cummins Platform

5.9L 12v (1989–1998)

The 12v is a mechanical engine with a stout bottom end and no emissions equipment in the way. It is the friendliest Cummins for a big single.

  • Street/tow with a P-pump: S467 or S472 on T4, 0.90–1.10 A/R
  • Street/strip: S476 on T4, 1.10–1.25 A/R
  • Sled pulling and drag: S480 through S488 on T6

Fuel is usually the limiter before the turbo is. A 12v on a stock P-pump will not use an S480.

5.9L 24v and Common Rail (1998.5–2007)

The 24v and later common rail 5.9 respond much the same as the 12v on the air side. Common rail trucks have the fuel system to support larger frames more readily.

  • First big single: S467 or S472 on T4
  • The common choice: S476 on T4 or T6, 1.10–1.25 A/R
  • 1,200+ WHP builds: S480 through S488 on T6

6.7L (2007.5–present)

The 6.7 has more displacement, which means it will spool a larger frame than a 5.9 at the same RPM. It also arrives with a variable geometry turbo and an exhaust brake you will lose in a fixed-geometry S400 swap — a real consideration if the truck tows.

  • Street/strip: S476 on T4 or T6
  • Four-digit builds: S480 through S488 on T6, 1.25–1.45 A/R
  • Still towing? Consider staying with an upgraded VGT instead — see 6.7 Cummins Turbo Upgrades

Quick Reference

Build Goal Size Flange A/R
First big single, street driven S467 / S472 T4 0.90–1.10
Street/strip, ~1,000 WHP S476 T4 or T6 1.10–1.25
Drag and pulling, 1,200+ WHP S480–S488 T6 1.25–1.45
Compound top charger S472–S480 T4 or T6 Match to bottom charger

Shop S400-Frame Turbos for Cummins

What Else the Swap Needs

The turbo is roughly half the parts list. A Cummins S400 swap also needs:

Exhaust Manifold

An aftermarket T4 or T6 manifold. This decision drives your flange choice, not the other way round — buy the manifold and the turbo to match each other.

Downpipe Flange and Clamp

Compressor Discharge

Compressor outlet discharge flange with clamp, sized to your charge pipe — 3.0", 3.5", or 4.0".

Oil Drain

S400 turbos are large frame, so you need a 50.8mm (2.00") bolt centre drain flange with a 12AN port. On Cummins applications the return usually goes into the block.

Wastegate

A fixed-geometry S400 on a divided or open housing needs an external wastegate and dump tube to control boost.

Heat Management

A turbo blanket keeps underhood temperatures down and helps maintain turbine inlet energy.

Compound Setups on Cummins

Compounds are extremely common on Cummins because they solve the one thing a big single gives up: low-end response.

The usual arrangement is an S400 as the atmospheric (low-pressure) charger feeding a smaller S300 or a factory-frame Holset as the high-pressure unit. The small turbo lights immediately and the S400 carries the top end.

  • Tow-and-race trucks: S472 or S475 over a stock-frame or S300
  • High-horsepower compounds: S480 and up over an S300

Match the S400 to the manifold pressure the high-pressure turbo will actually generate, not to the engine displacement alone.

What You Lose Going Fixed Geometry

Worth being honest about, because it catches people out on 6.7L trucks:

  • Exhaust brake. A fixed-geometry S400 has no VGT vanes, so factory exhaust braking goes away.
  • Low-end response. Expect the truck to feel lazier below roughly 1,800–2,000 RPM depending on size.
  • Towing manners. A big single will tow, but a properly sized VGT tows better.
  • Emissions equipment. An S400 swap is not compatible with a factory emissions setup on a 6.7.

If the truck is primarily a tow rig, an upgraded HE300VG is usually the better answer — see the 6.7 Cummins turbo upgrade guide.

Related Guides

Not sure what your build needs? Send the details through the Turbo Spec Form and we will spec it with you.

Frequently Asked Questions

What is the best S400 turbo for a 6.7 Cummins?

For a street/strip 6.7 targeting around 1,000 wheel horsepower, an S476 on a T4 or T6 flange with a 1.10–1.25 A/R is the most common choice. Builds chasing 1,200+ WHP typically move to an S480 through S488 on T6. If the truck still tows regularly, an upgraded variable geometry turbo is usually the better option.

What size S400 is best for a 5.9 Cummins?

An S467 or S472 on a T4 flange is the standard first big single on a built 5.9L, moving to an S476 for street/strip use. Fuel system capacity is usually the limiting factor before the turbo is.

Will an S400 fit a Cummins without other modifications?

No. An S400 swap requires an aftermarket T4 or T6 exhaust manifold, a matching downpipe flange and clamp, a compressor discharge flange sized to your charge pipe, a 12AN oil drain with a 50.8mm bolt centre, and an external wastegate on a fixed-geometry setup.

Do I lose the exhaust brake with an S400 on a 6.7 Cummins?

Yes. A fixed-geometry S400 has no variable geometry vanes, so factory exhaust brake functionality is lost. This is the main reason towing-focused 6.7 owners often stay with an upgraded VGT instead.

Should I run a single S400 or compounds on a Cummins?

A single S400 is simpler and makes strong top-end power. Compounds — an S400 feeding a smaller S300 or factory-frame turbo — preserve low-end response and towing drivability, at the cost of complexity and packaging. Trucks that both tow and race usually run compounds.

What oil drain does an S400 need on a Cummins?

A 50.8mm (2.00") bolt centre flange with a 12AN port, since S400 turbos are large frame. On Cummins applications the return typically goes into the block using a -12AN block drain fitting.