Automotive ·2 min read ·Reviewed October 12, 2026 ·By Meridian Parts

Short Block vs Long Block: What’s the Difference?

What a short block and a long block include, and how to choose between a short block, long block or complete engine.

When an engine fails, you can replace part of it or all of it. A short block is the bottom end of the engine; a long block adds the top end. Which one you need depends on what failed and how much of your old engine you can reuse.

What a short block includes

A short block is the engine block with the rotating assembly installed: crankshaft, connecting rods, pistons and rings, and the main and rod bearings. You reuse or buy separately the cylinder heads, valvetrain, timing parts, intake, exhaust manifolds, oil pan and accessories.

What a long block includes

A long block is a short block with the cylinder heads, camshaft(s) and valvetrain fitted, and usually the timing components. Intake, exhaust, fuel system, sensors and accessories are generally moved over from your old engine. Exactly what is included varies by builder, so check each listing.

Short block vs long block: which should you buy?

Choose a short block if the damage is in the bottom end (spun bearing, failed piston or rod, cracked cylinder) and your heads are in good condition, or you plan to fit upgraded heads.
Choose a long block if the heads or valvetrain are also worn or damaged, or you want a faster installation with fewer parts to transfer.
Choose a complete engine if you want the most ready-to-install option.

Cummins short and long blocks

Subaru short and long blocks

More guides: crate engine vs rebuild · rebuilt vs remanufactured · what comes with a long block.

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