S366 Turbo: Specs, Horsepower & Fitment Guide
The S366 is the most-installed turbo in the 300 frame, and it earned that position honestly. A 66mm (2.60") compressor sits at the point where you get a genuine power increase without the truck becoming something you have to drive around.
If you are new to single-turbo upgrades and reading conflicting advice, this is the size most of that advice eventually converges on. Black Sheep Industries builds the True North Turbos TNT366 66mm T4 to order in Canada.
S366 Specs
| Compressor inducer | 66mm (2.60") |
|---|---|
| Compressor wheel | Billet, machined from forged 2618 |
| Turbine wheel options | 76x68 or 80x73, billet |
| Turbine inlet | T4 bolt pattern, .88 A/R open or .91 A/R divided |
| Turbine discharge | 4.25" marmon |
| Compressor housing | 4" inlet, 2.5" outlet |
| Bearing | Journal, 360-degree thrust bearing |
| Oil drain bolt centre | 50mm (1.97") — mid frame |
| Max power (crank) | 1,090 HP |
Read 1,090 HP as a compressor ceiling rather than a build target — it is what the 66mm wheel will support at the edge of its map, not where the turbo is pleasant to run. The overwhelming majority of S366 builds sit well below it.
Why the 66mm Is the Default
Three reasons, and they compound.
1. It Does Not Force a Trade-Off
Smaller sizes trade top-end for response. Larger sizes trade response for top-end. The 66mm sits at the point where most builders find they are not really giving up either — the truck still behaves at low RPM and pulls meaningfully harder than stock.
2. It Matches Common Fuel Levels
Most builds arrive at a single-turbo upgrade with a fuel system that is modified but not extreme. A 66mm compressor is well matched to that reality. Going larger frequently means buying airflow the fuel system cannot use.
3. It Leaves Room to Grow
Because turbine housings are interchangeable across the 300 frame, an S366 is not a dead end. If the build evolves, a turbine wheel or housing change can shift its character without replacing the turbo.
Turbine Wheel Choice
The S366 is offered with the 76x68 and 80x73 turbine wheels.
- 76x68 — earlier response. The right call if the truck tows or is daily driven, or if you are prioritising the low-RPM feel.
- 80x73 — the more common pairing on a 66mm compressor, and the better balance for a truck that sees a mix of street and higher-RPM use.
Unlike the S363, where the smaller turbine is the more consistent recommendation, the S366 genuinely goes either way. Decide on how the truck is driven rather than on the power number.
See the turbine wheel and housing guide.
Fitment: What You Need to Order
- T4 manifold — open or divided to match the turbine housing
- 4.25" marmon turbine discharge flange and clamp — 3", 3.5" or 4". 3.5" is the common choice at this size.
- Compressor discharge v-band sized to your charge pipe
- Oil drain flange at 50mm (1.97") bolt centre, 10AN or 12AN
- External wastegate and dump tube — see wastegates
Full detail: S300 Turbo Flange Guide and S300 Turbo Oil Drain Guide.
S366 vs S363 vs S372
| S363 | S366 | S372 | |
|---|---|---|---|
| Inducer | 63mm (2.48") | 66mm (2.60") | 72mm (2.83") |
| Response | Quickest | Very good | Noticeably later |
| Top end | Lowest | Balanced | Highest of the three |
| Max power (crank) | 940 HP | 1,090 HP | 1,140 HP |
| Turbine options | 76x68, 80x73 | 76x68, 80x73 | 76x68, 80x73, 82x75 |
| Best for | Towing, compound HP charger | Almost everything | Street/strip |
The gap between the S363 and S366 is small. The gap between the S366 and S372 is where the decision gets real — that is the point at which you start paying for airflow with response.
Buy the TNT366
- TNT366 66mm T4 — built to order in Canada, billet forged 2618 wheels
- All TNT3R T4 turbochargers
Not sure? Send your build details through the Turbo Spec Form.
Related Guides
- S300 Turbo Guide
- What Size S300 Turbo Do I Need?
- S363 Turbo Guide · S372 Turbo Guide
- S300 Turbo for Cummins
Frequently Asked Questions
How much horsepower will an S366 support?
Up to 1,090 crank horsepower. That is a compressor ceiling rather than a target — what the 66mm wheel will support with the turbo at the edge of its map. Most S366 builds run far below it, and past roughly 820 HP a 400-frame turbo makes the same power with less strain.
Why is the S366 so popular?
It sits at the point in the 300 frame where you get a real power increase without a meaningful response penalty, and it matches the fuel systems most builds actually have when they reach a single-turbo upgrade.
S366 or S372?
The S366 if the truck is street driven, tows, or the fuel system is moderate. The S372 if the build has the fuel to use the extra airflow and you accept later boost onset in exchange for more top end.
What turbine wheel should I run on an S366?
The 80x73 is the more common pairing and the better balance for mixed street and higher-RPM use. The 76x68 is the better choice if the truck tows or is daily driven and you want the earliest response.
Is the S366 a good first single turbo?
Yes. It is the most-installed size in the frame precisely because it does not force a trade-off, and because turbine housings are interchangeable it leaves room to adjust character later without replacing the turbo.
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.