S300 Turbo Guide: Sizes, Specs, Flanges & Fitment

The S300 turbo is the most-installed single turbo in diesel performance. It is BorgWarner's 300-frame turbocharger family — the size class that covers everything from a first upgrade on a stock-appearing truck to the high-pressure charger in a compound setup, and the frame most builders actually live with day to day.

This guide covers what an S300 is, how the sizes are named, how turbine wheel and housing choices change the way it drives, and exactly which flanges, clamps and drains you need to make one bolt to your build. Black Sheep Industries manufactures S300 fitment hardware in-house and builds the True North Turbos TNT3R 300-frame turbocharger line in Canada.

What Is an S300 Turbo?

"S300" refers to BorgWarner's 300-frame turbocharger series. The number does not describe the compressor size. It describes the frame: the centre housing rotating assembly (CHRA), the bearing system, and the physical envelope the compressor and turbine wheels live in.

Within that one frame sits a wide range of compressor wheels. That is why you will see S362, S363, S364, S366, S369, S371, S372, S375, S376 and S380 — all of them are S300-frame turbos, and all of them share the same core architecture, oil feed and drain geometry, and mounting hardware.

The S300 came out of medium-duty commercial diesel service before the performance aftermarket adopted it as the default single-turbo upgrade. It remains the frame of choice for anyone who needs the truck to still behave — tow, daily drive, respond off idle — while making meaningfully more power than stock.

What Does the Number After "S3" Mean?

The two digits following the frame designation refer to the compressor wheel inducer diameter in millimetres. An S363 has a 63mm (2.48") compressor inducer. An S372 has a 72mm (2.83") inducer. An S380 has an 80mm (3.15") inducer.

Larger inducer means more airflow and more horsepower potential — but also more rotational mass and later spool. Because the 300 frame is chosen for response as much as for power, size selection here matters more than it does on a bigger frame. Going two sizes up on an S300 can cost you the exact quality you bought the frame for.

S300 Turbo Sizes and Power Ceilings

Every S300 uses the same frame, so stepping up in size does not change your mounting hardware — only the airflow.

Size Compressor Inducer US Standard Typical Application Max Power (crank)
S363 63mm 2.48" First upgrade, towing, stock-appearing builds 940 HP
S366 66mm 2.60" The most popular all-around S300 size 1,090 HP
S369 69mm 2.72" Street/strip, compound high-pressure charger 1,120 HP
S372 72mm 2.83" Serious street/strip, heavier compound duty 1,140 HP
S376 76mm 2.99" Top-end 300-frame single 1,210 HP
S380 80mm 3.15" Maximum airflow within the 300 frame 1,300 HP

These are compressor ceilings, not recommendations. They are the maximum crank horsepower the compressor will support with the turbo working at the edge of its map. What you actually make depends on displacement, fuel system, head studs, tune and turbine housing selection — a 6.7L Cummins and a 5.9L will not make identical numbers on the same turbo. For where we would actually move you across to the 400 frame, see the sizing guide below.

Full sizing walkthrough: What Size S300 Turbo Do I Need?

Replacing an existing turbo? The S300 replacement turbo cross-reference maps S363 through S380 to direct True North Turbos equivalents.

Above 80mm you leave the 300 frame entirely and move into 400-frame territory — see the S400 turbo guide.

A Note on S376, S380 and the 400 Frame

The 300 frame and the 400 frame overlap on paper at the top of the range. A 76mm compressor exists in both. They are not the same turbo. The S376 is a 76mm compressor in a 300-frame centre section with 300-frame turbine wheels, a 4.25" turbine discharge and a 50mm (1.97") drain bolt centre. An S476 is a 76mm compressor in a physically larger 400-frame centre section with a 4.62" or 5.75" discharge and a 50.8mm (2.00") drain bolt centre. Same compressor number, completely different hardware. Order accordingly.

Shop S300-Frame Turbochargers

S300 vs S400: What Is the Difference?

This is the most common question builders ask before committing to a manifold and downpipe, and the answer matters because the two frames are not interchangeable.

  • Frame size. The S300 is the smaller 300-frame turbo, typically 63–80mm (2.48–3.15") on the compressor. The S400 is physically larger in every dimension.
  • Spool. The S300 spools noticeably earlier. This is the reason to buy one.
  • Power ceiling. An S400 runs well past where the 300 frame gives up.
  • Mounting. Different turbine discharge sizes, and a different oil drain bolt centre — 50mm (1.97") on the 300 frame against 50.8mm (2.00") on the 400. Moving between frames means new downpipe hardware and new drain fittings.
  • Compound setups. Many high-power builds run both, with the S300 as the high-pressure charger fed by an S400.

If the truck tows and you want to keep the drivability you have, the S300 is usually the smarter pick. If you are chasing four-digit power on a single, the 400 frame is where you start.

Full comparison: S300 vs S400 Turbo — Which Frame Is Right for Your Build?

S300 Turbine Flanges: T4 and What You May Be Replacing

The turbine inlet flange determines how the turbo mounts to your exhaust manifold. Every True North Turbos TNT3R is built on the standard T4 bolt pattern, available in open (undivided) or divided configuration.

  • T4 open — one undivided turbine inlet. Simpler, pairs with an open manifold, the common choice on street builds.
  • T4 divided — a split inlet that keeps exhaust pulses separated from the manifold into the turbine. Better pulse energy and earlier response on a divided manifold. Only worth it if your manifold is actually divided.

Plenty of S300s in the field are on a T3 flange — smaller footprint, common on older and OEM-derived applications. TNT3R does not offer a T3 turbine housing, so a T3-to-T4 move means a new manifold. If you are replacing a T3 S300, start with the cross-reference guide so you know what else changes.

Note that bolt pattern is the correct term for a turbine inlet flange — it is a genuine four-bolt pattern. The oil drain flange is a different animal and is specified by bolt centre. See the drain section below.

S300 Flanges, Clamps and Fitment Hardware

This is where most S300 swaps stall. The turbo bolts up, and then the downpipe, the compressor outlet and the oil drain all need parts that are not in the box. Black Sheep Industries machines this hardware in-house so you are not sourcing four parts from four suppliers.

Turbine Discharge — 4.25" Marmon

S200 and S300 turbine housings use a 4.25" marmon discharge.

The most common ordering mistake on this frame: the S400 T4 half marmon is 4.62" (117mm). It is close enough to 4.25" to look right in a photograph and it will not clamp. If you are stepping down from a 400-frame turbo, or buying used hardware described only as "marmon," measure it before you order.

Compressor Discharge

TNT3R turbos use a compressor housing with a 4" inlet and a 2.5" outlet. Your compressor discharge v-band is sized to the charge pipe you are running, not to the housing outlet.

Oil Drain

A drain flange is defined by three independent specs. Get all three right and it fits, flows and clears.

1. Bolt centre — what physically bolts on. Measure from the centre of one bolt hole to the centre of the other on the turbo's drain pad:

Bolt Centre US Standard Frame Class
38mm 1.50" Small frame
50mm 1.97" Mid frame — this is your S300
50.8mm 2.00" Large frame

Mid and large frame are only 0.8mm apart, about 1/32 of an inch, so measure with calipers rather than a tape.

2. Port size — whether it flows enough oil. Unlike the 400 frame, where 12AN is the only sensible answer, the 300 frame gives you a real choice. 10AN is adequate for most street and towing S300 builds. 12AN buys margin on hard-worked, high-boost or compound applications where oil return is doing more work. Both are offered in the 50mm (1.97") mid-frame bolt centre.

3. Drain length — what it clears on the way out. The figure in each product name is the length of the drain, meaning how far the drain body stands off the flange face before your hose connects. Pick the shortest one that clears everything around your drain pad.

Thread options are M8-1.25 (metric, roughly 5/16") or 3/8-16 (US standard coarse).

Full breakdown, with routing rules and a leak diagnosis table: S300 Turbo Oil Drain Guide

Complete Fitment Checklist

  • Turbine inlet: T4 manifold, open or divided to match your turbine housing
  • Turbine discharge: 4.25" marmon flange and clamp — not the S400's 4.62"
  • Compressor discharge: v-band flange and clamp sized to your charge pipe
  • Oil feed line and restrictor appropriate to your bearing type
  • Oil drain flange at 50mm (1.97") bolt centre, in 10AN or 12AN, in a length that clears your install, plus matching drain hose and return fitting
  • External wastegate and dump tube if running a divided or open housing
  • Turbo blanket for underhood heat management
  • Turbine and compressor housing gaskets — see replacement o-rings and gaskets

Full breakdown, with measuring instructions and a complete SKU table: S300 Turbo Flange Guide

S300 Turbine Wheels and Housings

On the 400 frame, A/R is the big turbine-side lever. On the 300 frame it is not — the housings run 0.88 A/R open and 0.91 A/R divided, and that small a spread will not transform how the turbo drives. The turbine wheel is the decision that matters here.

Turbine Wheel Character Available On
76x68 Earliest response, lowest top-end flow TNT363, TNT366, TNT369, TNT372
80x73 The balanced middle, and the default on most builds TNT363, TNT366, TNT369, TNT372
82x75 Most turbine flow, latest response TNT369, TNT372, TNT376, TNT380

Housings are interchangeable across the frame, so a turbine housing is an upgrade path rather than a one-time decision.

Full breakdown: S300 Turbine Wheels and Housings Explained

S300 Turbos by Platform

Cummins 5.9L and 6.7L

The 5.9L 12v and 24v Cummins is the classic S300 host, and the 6.7L follows the same pattern. An S363 or S366 on a T4 flange is the standard first big single; builds pushing harder move to S369 and up. Both require an aftermarket T4 manifold and full drain hardware.

Full guide: S300 Turbo for Cummins

Duramax LBZ, LMM, LML and L5P

Because the Duramax mounts its turbo in the valley, an S300 conversion requires more fabrication than a Cummins swap — plan for a full kit and dedicated up-pipes, not just a turbo.

Full guide: S300 Turbo for Duramax

Power Stroke 6.0L, 6.4L, 6.7L and 7.3L

The 6.0L Power Stroke is a common S300 platform — the factory VGT is a known weak point, and a fixed-geometry S300 conversion is a durability upgrade as much as a power upgrade.

Full guide: S300 Turbo for Power Stroke

Compound Setups

An S300 is the standard high-pressure charger in a compound arrangement, sitting under a larger atmospheric turbo. It sees boosted air rather than atmosphere, which changes how you size it — a smaller S300 than you would run as a single is usually correct. This is the opposite role from the S400, which is normally the atmospheric charger in the same setup.

Choosing the Right S300 for Your Build

First Upgrade, Tows, Daily Driven

S363 or S366 with the 76x68 or 80x73 turbine. You give up top-end for response you will actually use every day.

Street/Strip Single

S369 or S372 with the 80x73 or 82x75 turbine. The broadest useful range on the frame.

Maximum Single-Turbo Airflow

S376 or S380 with the 82x75 turbine. At this end of the frame, honestly compare against a small S400 — you may be paying 300-frame spool penalties for power a 400 would make more comfortably.

Compound High-Pressure Charger

S363 through S369 depending on the atmospheric turbo above it. Size for the manifold pressure it will actually see, not for the power target of the whole system.

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

Why Buy S300 Hardware From Black Sheep Industries

  • S300 flanges, clamps and drains machined in-house — not resold imports
  • Flange and clamp sold together so fitment is right the first time
  • 304 stainless and aluminum options on the turbine discharge flange
  • Both 10AN and 12AN drains stocked in the 50mm (1.97") mid-frame bolt centre, in three lengths
  • Metric and US standard thread options on drain hardware
  • True North Turbos 300-frame turbochargers built to order, assembled and balanced in Canada
  • Billet compressor and turbine wheels machined from forged 2618
  • Priced in CAD with US customs and duties covered
  • Direct support from people who build these setups, not a call centre

The Complete S300 Guide Series

Sizing and Selection

Fitment and Hardware

By Frame Size

By Platform

Shop

Background Reading

Frequently Asked Questions

What is an S300 turbo?

An S300 turbo is a BorgWarner 300-frame turbocharger. The designation refers to the frame size — the centre housing, bearing system and physical envelope — not the compressor wheel. S363, S366, S369, S372, S376 and S380 are all S300-frame turbos with different compressor wheels.

How big is an S300 turbo?

The number after S3 is the compressor inducer diameter in millimetres. S300-frame turbos commonly range from 63mm (2.48") to 80mm (3.15") on the compressor. All of them share the same frame, oil drain geometry and mounting hardware regardless of compressor size.

What is the difference between an S300 and an S400 turbo?

The S300 is the smaller 300-frame turbo and spools noticeably earlier. The S400 is a larger 400-frame turbo with a higher power ceiling. They use different turbine discharge sizes and different oil drain bolt centres — 50mm (1.97") on the 300 frame against 50.8mm (2.00") on the 400 — so they are not interchangeable without changing hardware.

What size downpipe flange does an S300 use?

S200 and S300 turbine housings use a 4.25" marmon discharge. This is close to but not the same as the S400 T4's 4.62" (117mm) half marmon, and the two will not clamp together. Black Sheep Industries sells the 4.25" flange and its quick-release clamp as a set.

What size oil drain does an S300 turbo need?

S300 turbos are mid frame, which means a 50mm (1.97") bolt centre drain flange. Bolt centre is the distance between the centres of the two bolt holes on the drain pad — 38mm (1.50") is small frame and 50.8mm (2.00") is large frame, so measure with calipers before ordering. Port size is a separate choice of 10AN or 12AN, and drain length — the 35mm/65mm/100mm figure in the product name — is a separate clearance choice again.

Is an S300 a T3 or a T4?

Both exist in the field, but every True North Turbos TNT3R is built on the T4 bolt pattern, in open or divided configuration. Replacing a T3 S300 with a TNT3R means moving to a T4 manifold.

Can an S300 be used in a compound setup?

Yes. The S300 is the standard high-pressure charger in a compound arrangement, sitting under a larger atmospheric turbo such as an S400. Because it sees boosted air rather than atmosphere, a smaller S300 than you would run as a single is usually the correct choice.

How much horsepower can an S300 turbo support?

It depends on the size. Maximum crank horsepower within the 300 frame runs from 940 HP on an S363 up to 1,300 HP on an S380. Those are compressor ceilings — the number the compressor will support with the turbo working at the edge of its map, hot and inefficient. They are not where we would advise you to run one. In practice we recommend moving to a 400-frame turbo around 820 HP, where an S400 makes the same power comfortably and leaves room to grow.

Power ratings on this page are quoted in crank horsepower (HP). Figures previously published in wheel horsepower (WHP) have been restated using our in-house tested conversion — the hardware and its capability are unchanged.