S300 Turbine Wheels and Housings Explained

On the 400 frame, A/R is the big turbine-side lever — housings span 0.90 to 1.45 and the choice genuinely changes the character of the turbo. The 300 frame does not work that way. TNT3R turbine housings run 0.88 A/R open and 0.91 A/R divided, and a 0.03 spread is not what decides how your turbo drives.

On this frame, the turbine wheel is the decision. This guide covers what the three wheels do, when open and divided actually matter, and how to think about the exhaust side without over-indexing on a number that barely moves.

The Three Turbine Wheels

Every TNT3R turbine wheel is billet, machined from forged 2618. The designation is exducer x inducer in millimetres — an 80x73 wheel has an 80mm exducer and a 73mm inducer.

Turbine Wheel Character Choose It When Available On
76x68 Earliest response, lowest top-end flow Towing, daily driving, smaller compressors, compound high-pressure duty TNT363, TNT366, TNT369, TNT372
80x73 The balanced middle Most builds. The default for a reason. TNT363, TNT366, TNT369, TNT372
82x75 Most turbine flow, latest response Larger compressors that need the exhaust side to keep up, higher-RPM use TNT369, TNT372, TNT376, TNT380

How to Read That Table

A smaller turbine wheel is easier for exhaust gas to spin up, so boost arrives sooner. The trade is that at high flow it becomes a restriction — backpressure climbs, and the engine spends energy pushing exhaust past a wheel that has run out of capacity.

A larger turbine wheel flows more at the top but needs more exhaust energy to get moving, so response softens off idle.

The right answer is the smallest wheel that does not choke at your intended RPM and power. Most people pick too large.

Matching Turbine Wheel to Compressor

The compressor and turbine are one decision, not two. A few practical pairings:

  • Small compressor, small turbine (S363 or S366 with 76x68) — the quickest-responding combination in the frame. Ideal for towing and for compound high-pressure duty.
  • Small compressor, larger turbine — rarely what you want. You give up response without gaining meaningful airflow, because the compressor is the limit.
  • Mid compressor, 80x73 (S369 or S372) — the broadest useful combination on the frame.
  • Large compressor, 82x75 (S376 or S380) — necessary pairing. Putting a 76x68 behind an 80mm compressor creates a turbine-side restriction that caps the whole setup.

If you are trying to add top-end without losing low-end, moving up a turbine wheel while holding the compressor is often a better move than moving up a compressor size.

Open vs Divided Housings

This is a genuine decision, and it is decided by your manifold rather than by preference.

T4 Open (Undivided), 0.88 A/R

  • One undivided turbine inlet
  • Pairs with an open T4 manifold
  • Simpler, and the common choice on street builds

T4 Divided, 0.91 A/R

  • Split inlet that keeps exhaust pulses separated from the manifold into the turbine
  • Better use of pulse energy, which shows up as earlier response
  • Only delivers that benefit on a genuinely divided manifold. A divided housing on an open manifold gives you the divider without the pulse separation, which is most of the cost and none of the gain.

If your manifold is divided, buy divided. If it is open, buy open. Do not buy a divided housing on the assumption you will change manifolds later — buy it when you change manifolds.

Why A/R Is a Smaller Story Here

The 0.88 and 0.91 figures are not a selection matrix. They come paired with the open and divided housings respectively, so in practice you are not choosing an A/R at all — you are choosing open or divided, and the A/R follows.

This is a real structural difference from the 400 frame, where housings span 0.90 through 1.45 and A/R selection is a meaningful lever on how the turbo behaves. If you have read S400 material and come here expecting the same range of choice, that is why it is not here.

What that means practically: on a 300-frame build, put your attention on turbine wheel selection and manifold design. Those are where the exhaust-side gains actually live.

Housings Are an Upgrade Path

TNT3R turbine housings are interchangeable across the frame. A turbine housing is not a one-time decision welded to the turbo you bought — it is a component you can change later as the build changes.

If you are running an 82x75 turbine and need a matching housing, contact us through the Turbo Spec Form — that combination is not currently listed as a standalone housing variant.

Related Guides

Frequently Asked Questions

What turbine wheels are available on an S300?

True North Turbos TNT3R turbochargers are offered with 76x68, 80x73 and 82x75 billet turbine wheels, machined from forged 2618. Availability varies by compressor size — the 82x75 is offered on the larger compressors where the exhaust side needs to keep up.

What A/R does an S300 turbine housing use?

TNT3R turbine housings are 0.88 A/R in the open configuration and 0.91 A/R divided. Unlike the 400 frame, which spans roughly 0.90 to 1.45, the 300 frame's A/R is effectively determined by whether you choose open or divided rather than being a separate selection.

Should I run an open or divided turbine housing?

Match it to your manifold. A divided housing only delivers its pulse-separation benefit on a genuinely divided manifold; on an open manifold you carry the divider without the gain. If your manifold is open, buy open.

Is a bigger turbine wheel always better?

No. A larger turbine wheel flows more at high RPM but needs more exhaust energy to spin up, so response softens. The right choice is the smallest wheel that does not become a restriction at your intended power and RPM.

Can I change the turbine housing later?

Yes. TNT3R turbine housings are interchangeable across the frame, so the housing is an upgrade path rather than a permanent decision made at purchase.