What engine came in a 1956 GMC truck?
The short answer: there wasn’t a single engine across the 1956 GMC truck lineup. The range offered more than one powerplant depending on model and configuration.
In more detail, the 1956 GMC trucks, produced during GM’s Advance-Design era, could be powered by either a GMC-built inline-six or a Chevrolet small-block V8. The exact engine you’d find depended on the specific truck model (half-ton, 3/4-ton, etc.), regional market, and the options chosen at purchase.
Common engine options in the 1956 GMC lineup
These are the engines most frequently associated with 1956 GMC trucks. The actual installed engine varied by model and production batch.
- 270 cubic-inch inline-six — GMC’s own six-cylinder engine used in many light- and medium-duty trucks of that era.
- 265 cubic-inch Chevrolet small-block V8 — GM’s new V8 option introduced in the mid-1950s and made available in several GMC truck configurations in 1956.
The exact engine in a given vehicle can depend on the model year’s build sheet, body style, and market. For precise identification, check the vehicle’s data plate, engine stamping, or original build documentation.
How to confirm which engine your 1956 GMC truck has
Verifying the correct engine type is key for restoration, parts compatibility, and maintenance scheduling.
Check the engine code and stamping
Look for the engine displacement and model code stamped on the block or on a nameplate on the valve cover. This will identify whether the engine is the GMC 270 inline-six or the Chevrolet 265 V8 (or another option that may have been installed).
Consult the data plate and VIN/build sheet
The data plate or build sheet (sometimes found in the glove box, under the seat, or via the glove box label) can confirm the original drivetrain. Cross-reference your VIN with GMC or GM historical databases to verify the factory-installed engine.
Summary
In 1956 GMC trucks, you typically had at least two engine options: the 270 cubic-inch inline-six and the 265 cubic-inch Chevrolet small-block V8. The exact engine depended on the model and options chosen when the truck was built. For owners and restorers, verification through the engine stamping, data plate, or build sheet is the best way to confirm which powerplant is in a specific vehicle.
