When it comes to replacing your diesel engine, you’ll likely hear the terms “short block” and “long block” thrown around.

So what’s the difference between a short block engine and a long block engine?

A short block engine includes your basic block with connecting rods, pistons, and a crankshaft. Your long block engine is a short block plus your cylinder heads, camshaft, and valve-train.

Note that “short block” and “long block” engines have absolutely nothing to do with their length. It’s the components that we’re looking at, and the same terms are used for both diesel engines and gas engines.

The Bare Block 

The most basic, stripped-down sort of engine block you can find is the bare block.

It’s exactly what the name implies. There are no internal components to it– no pistons, rods, or crankshaft.

The Short Block and The Long Block

The short block is actually a bare block but includes the connecting rods, the pistons, and a crankshaft.

Depending on the style of the engine, it may also include a camshaft in it if it’s not an OHC (an overhead cam) engine.

But essentially, the main differentiation between a short block and a long block is the inclusion of the cylinder heads. A short block engine doesn’t have any cylinder heads.

Meanwhile, a long block has the cylinder heads, as well as a camshaft (in most cases), and a valve train. 

There are a lot of components that can be included (or not included) with a long block such as valve covers, the intake manifold, the exhaust manifold, pickup tube, oil pan, oil cooler, and flywheel housing, among others.

The Turn-Key Engine 

Finally, you have the complete engine, which is also known as a “turn-key” engine. As it is fully assembled, the manufacturer ships this engine in a crate, and all the installer has to do is fit this engine into a vehicle. All one has to do is turn the key and drive off.

The complete engine includes everything. Essentially, how your engine is running inside your truck and you take it out, that’s exactly what we’re looking at. Typically, complete engines are what we are likely to purchase the most, and sometimes, it’s the only way we’ll purchase an engine.

A complete turn-key engine is a basic long block plus your fuel system, turbos, and electricals like the alternator, starter, power steering system, and then all the tin components like the covers, oil pan, and front cover, and the ECM and wiring harness.

Many times, there are a few of the smaller components missing on a complete engine (which we can easily work with), but for a complete engine, the essentials need to be there.

This means you have a good long block, all the engine covers, the turbo, and a complete fuel system.

Choosing the Right Engine Block

Usually, a long block engine will offer better and more reliable performance than a short block engine. 

That’s because long blocks come with more parts preinstalled, which means they are less likely to malfunction due to faults in the fitting process. In addition, components that come with a long block wear out evenly and, consequently, minimize replacement costs.

Note, however, that not all long blocks may work well with the make and model of your vehicle. You have to make sure that the long block to be installed is compatible with the electronic control unit and the transmission system of your car.

On the other hand, a short block engine allows you a greater degree of customization as you have more choice over the range of parts you can install. 

You can expect a short block to perform better than a long block if you invest in quality parts and accessories. Unlike a long block, a short block does not come with a preinstalled cylinder head. This means you have the freedom to choose whichever head meets your performance requirements. A good choice of head on a short block can actually produce more power than a stock engine.