GM Gen V 6.6L Gasoline V8 L8T: Specs, Engine Codes, Controllers & Maintenance
Engine Information · GM · Small-block · Gen V · Heavy duty
Gen V 6.6L Gasoline V8 L8T
The L8T is GM’s naturally aspirated gasoline workhorse for modern HD pickups and vans. Its iron block, long-stroke V8 layout and conventional eight-cylinder operation suit sustained load without diesel aftertreatment complexity.
Engine construction
| Specification | Details |
|---|---|
| Capacity / layout | 6.6L · 90° V8 |
| Construction | Iron block · aluminum heads |
| Valve gear | OHV · 2 valves per cylinder · variable cam timing |
| Fuel / induction | Direct injection · naturally aspirated |
| Valves / cylinders | 16 valves · no AFM / DFM |
| Oil example | 2026: dexos1 5W-30 · 7.6L / 8.0 U.S. qt with filter |
Codes & output
| RPO / version | Power / torque | Key difference |
|---|---|---|
| L8T | 401 hp / 464 lb-ft | HD pickup / current van rating |
SAE horsepower; torque in lb-ft. Ratings are for the stated application and fuel, rather than every vehicle with this RPO.
Vehicles & model years
| Brand | Model | Model years | Platform / chassis | Engine RPO |
|---|---|---|---|---|
| GMC / Chevrolet | Sierra / Silverado 2500HD & 3500HD | 2020–2026 | T1XX HD | L8T |
| GMC / Chevrolet | Savana / Express | 2021–2026 | GMT610 | L8T |
U.S. and Canadian applications within the 2005–2026 matrix scope. Engine availability depends on trim, build date and emissions certification.
Engine controllers
| Application / revision | ECM or PCM | Identification & function |
|---|---|---|
| 2020–2023 HD pickups | GM E93 ECM | Direct injection, cam timing, electronic throttle and working-load torque management |
| 2024–2026 HD pickups | GM E93 ECM · Global B generation | Different vehicle/security architecture despite the same controller family name |
| Van applications | VIN-specific GM ECM / calibration | Confirm van service number; HD pickup hardware is not a universal van replacement |
Identify the module from its service number, operating-system ID and VIN. The ECM/PCM and transmission controller have separate calibrations on many applications; a matching RPO alone does not make a replacement module plug-and-play.
Common issues & maintenance
- Valve-spring faults on specified buildsGM PIP5752 documents broken springs on certain 2020–2021 vehicles. A misfire with noise needs a spring and compression inspection.
- Fuel / ignition misfiresVerify injector operation, pressure and spark before assuming a failed lifter; L8T has no AFM or DFM.
- Leaks and lubricationRepair oil/coolant leaks promptly and use the correct oil/filter. Replacement engines require the GM prelubing procedure.
Keep it healthy. Use the HD/van maintenance schedule for towing and prolonged idling. Keep the cooling stack clean and verify actual oil pressure when warnings appear. Match the ECM generation and transmission calibration to the vehicle build.
References & technical sources
| Source | Reference |
|---|---|
| GM applications & RPO diagnostic matrices | View source |
| HP Tuners E90 / E93 production applications | View source |
| HP Tuners E93 Global B HD applications | View source |
| GM PIP5752G: valve springs | View source |
| GM TechLink 2026 U.S./Canada oil chart | View source |
