Subaru Engines: Which Ones Are Closed Deck and Why It Matters for Performance

Subaru is no doubt one of the most popular car brands among car enthusiasts. In particular, its engines have garnered a lot of attention due to their reliability, power output, and versatility. Among the various engine types available in Subaru models, the term "closed deck" is often referred to by car enthusiasts. But what exactly is a closed deck engine? And why does it matter for performance? In this article, we will delve deeper into these questions and explore which Subaru engines are closed deck.

What is a Closed Deck Engine?

Before we delve into what a closed deck engine is, let’s first recap what an engine block is. The block is the foundation of the engine, and it contains the cylinders, crankshaft, pistons, and other parts critical to the engine’s functioning. In a typical engine block, the cylinders and water jacket are cast as a single unit in an open design, meaning that the wall thickness of the cylinder area is relatively thin.

A closed deck block, on the other hand, has an additional wall of material that separates each cylinder bore. This added material is referred to as "webbing," and it creates a more robust, solid structure around the cylinder bore. The webbing also provides extra support for the cylinder walls, making them less prone to flexing and cracking under extreme loads.

Advantages of a Closed Deck Engine

The primary advantage of a closed deck engine is its increased strength and rigidity. The added webbing around the cylinder bore provides extra support to resist cylinder wall flexing, helping to prevent cylinder wall cracking under extreme loads. A closed deck block is especially beneficial in high-performance applications, where the engine is subject to high levels of boost and/or cylinder pressures. In these situations, the block’s structural integrity is essential to the durability of the engine.

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Another advantage of a closed deck engine is improved heat dissipation. The webbing design of a closed deck block provides additional surface area for heat transfer from the cylinder bores to the coolant passage, allowing the engine to run cooler. This benefit is particularly useful in turbocharged or high-performance engines, where high cylinder pressures can generate more heat than an open deck block can effectively handle.

Disadvantages of a Closed Deck Engine

While there are many advantages to a closed deck engine, there are also some drawbacks. One of the main disadvantages is the increased cost. The added webbing in a closed deck block requires extra machining time and material, which translates to higher production costs.

Another disadvantage is the additional weight. The extra material needed in a closed deck block makes it heavier than an open deck block. While this may not be an issue in many applications, it can negatively impact certain performance characteristics, such as handling and acceleration.

Subaru Engines That Are Closed Deck

Now that we have a better understanding of what a closed deck engine is and its advantages and disadvantages, let’s take a closer look at which Subaru engines are closed deck. While not all Subaru engines are closed deck, many of their high-performance engines are. Here are some of the most popular Subaru closed deck engines:

  • EJ20G: This engine was used in the first generation Subaru Impreza WRX GC8 and was only available in the Japanese domestic market (JDM). It has a closed deck block, forged internals, and a single turbocharger.

  • EJ207: This engine was used in the second-generation Subaru Impreza WRX STI and is also a JDM-only engine. It has a closed deck block, forged internals, and a twin-scroll turbocharger.

  • EJ255: This engine is used in the Subaru Legacy GT and the Subaru Impreza WRX from 2005 to 2009. It has a closed deck block and is equipped with a single turbocharger.

  • EJ257: This engine is used in the Subaru Impreza WRX STI and is a staple in the high-performance Subaru community. It has a closed deck block, forged internals, and a durable semi-closed deck design. The engine also features a more advanced AVCS (Advanced Valve Control System) than its predecessor, the EJ207.

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Frequently Asked Questions

Q1: Are all Subaru engines closed deck?

No, not all Subaru engines are closed deck. However, many high-performance Subaru engines, particularly those used in the WRX and STI models, are closed deck for added strength and durability.

Q2: Can a closed deck block be used for street applications?

Yes, a closed deck block can be used for street applications. In fact, many Subaru enthusiasts use closed deck engines in their street cars for added durability and performance.

Q3: How much weight does a closed deck add to an engine?

The added weight of a closed deck block varies depending on the engine. However, in general, a closed deck block can add anywhere from 10-25 pounds to the overall weight of the engine.


In conclusion, a closed deck engine block provides added strength and rigidity, which is essential in high-performance applications. Subaru has utilized closed deck blocks in many of its high-performance engines, including the popular EJ257 found in the Impreza WRX STI. However, there are also some drawbacks, such as increased cost and weight, to consider. When it comes to Subaru engines, it’s important to choose the engine that best fits your specific needs and requirements, whether it’s a closed deck or open deck design.

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Alton Brobst

As a longtime Subaru enthusiast, Alton brings a wealth of knowledge and experience to our blog. From his early days of tinkering with engines to his current role as a certified Subaru technician, Alton has seen it all when it comes to Subarus. When he's not working on cars, he enjoys hiking and exploring the great outdoors.

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