different types of deck design in engine

Open deck design 

An open deck is one of the most common designs found in lower horsepower aluminum blocks. It is the easiest to manufacture and provides the overall best cooling efficiency, due to the coolants ability to make full contact with the surface area of the upper portion of the cylinder. Some will argue that this block has the benefit of weighing less than its two siblings because less material is used, but this weight difference is marginal for most blocks.

The downside to an open deck is that it provides the least amount of structural support at the top of the cylinder walls, where they need it most. This reason alone makes an open deck block the least reliable choice for almost any type of forced induction or nitrous application, and should be left to low compression, naturally aspirated engines and low boost platforms.

Semi-open/closed deck design 

A semi-closed deck is the most common design found in modern factory turbocharged aluminum blocks, and is stronger than an open deck by adding structural support to the top of the cylinders at four points. Using modern casting techniques, this design can handle respectable boost levels into the mid 30 PSI range and a much higher peak cylinder pressure than an open deck (depending on the application).

Because of the added material around the cylinder walls, this style is more difficult to manufacture and requires more machine work before the cylinders can be installed. Some will argue that the added support joints of a semi-closed deck reduces cooling efficiency and is more prone to cylinder hot spots by limiting the surface area for the coolant to contact. At higher horsepower levels, a semi-closed deck is still prone to failure at the points in between the supporting joints, especially in endurance racing or road racing applications where sustained high temperatures are common.

The most common solution for semi-closed and open deck blocks is installing aftermarket sleeves that can support higher cylinder temps and pressure. This process is pretty expensive, but it is highly recommended that you find a reputable machine shop that has experience with your platform. Sleeving requires a lot of precise machine work to not damage the block, so only the best in your area should be trusted.

Closed deck design 

A closed deck design is generally left to iron blocks and aluminum racing engines. It is the perfect design for fully built, high compression, high revving race engines that require the highest level of structural support available. Common on high level drag race motors, this design is also able to withstand prolonged periods of high heat and cylinder pressure commonly seen in endurance racing and road racing.

A closed deck block is much more expensive and requires an entirely different casting procedure if done from the manufacturer, but can also be modified using pieces that are press fit into position around the water jackets. The latter process requires a custom head gasket, along with precise calculations and machine work to verify that the pieces fit properly and that the water ports are drilled properly to provide adequate flow to efficiently cool the heads.

Many will also note that a closed deck block provides the least amount of cooling capability out of the three. Although this is true to an extent, many of todays closed deck blocks have been put through extensive testing and are designed to guarantee efficient cooling.