See other engines in this family
The same engine also has a main page: Chevrolet L8T.
GMC L8T specs: 401 ci (6.6L) 8-cylinder, 4.065 x 3.858 in (103.3 x 98 mm) bore and stroke, 10.8:1 compression. Rated 401 hp, 2020–2026.
The GMC 403ci (L8T) is oversquare — the 4.065" bore exceeds the 3.858" stroke by 5.4% — a layout that favors airflow and RPM over leverage at the crank. The 3.858" stroke puts mean piston speed at 4,000 ft/min around 6,200 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 50.1 ci (821 cc).
10.8:1 is in the range that usually runs on pump premium.
It is one of 9 engines in the GMC 403ci family, the smallest at 401 ci. 7 factory variants share these dimensions, rated at 401 hp across 2020–2026.
| Displacement | 401 ci / 6.6 L |
|---|---|
| Bore | 4.065" |
| Stroke | 3.858" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 10.8:1 |
| Bore/stroke ratio | 1.054 |
| Fuel type | gas |
|---|---|
| Redline | 5,600 rpm (factory limit) |
| Advertised HP | 401 hp |
| Years | 2020–2026 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 2020 | L8T net | 401 @ 5200 * | 464 lb-ft @ 4000 * | — |
| 2021 | L8T net | 401 @ 5200 * | 464 lb-ft @ 4000 * | — |
| 2022 | L8T net | 401 @ 5200 * | 464 lb-ft @ 4000 * | — |
| 2023 | L8T net | 401 @ 5200 * | 464 lb-ft @ 4000 * | — |
| 2024 | L8T net | 401 @ 5200 | 464 lb-ft @ 4000 | 10.8:1 |
| 2025 | L8T net | 401 @ 5200 | 464 lb-ft @ 4000 | 10.8:1 |
| 2026 | L8T net | 401 @ 5200 | 464 lb-ft @ 4000 | 10.8:1 |
Factory specification sheet. * Not yet cross-verified.
| Bore/stroke character | 1.054 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,858 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 50.1 ci |
| Static compression | 10.8:1 — in the range that usually runs on pump premium |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 2020 | 401 hp | L8T |
| 2021 | 401 hp | L8T |
| 2022 | 401 hp | L8T |
| 2023 | 401 hp | L8T |
| 2024 | 401 hp | L8T |
| 2025 | 401 hp | L8T |
| 2026 | 401 hp | L8T |
4 factory vehicles, 2020–2026. Each year opens that model's engine table.