The FA20 lives in two very different kinds of car. In the WRX it is a 2.0L turbo engine from the factory. In the BRZ, FR-S and 86 it is a naturally aspirated boxer that a lot of owners eventually want to turbocharge or supercharge. Either way, the same question shows up once the power plans get serious: the factory block is an open-deck design, so what happens to it under more boost? If you are searching for an FA20 closed deck alternative, this post covers the questions FA20 owners actually ask before deciding.
Is the FA20 block really open deck, and does that matter?
Yes. In an open-deck block the tops of the cylinder walls are not tied to the outer block by a solid deck, so the cylinders stand free at the top, surrounded by coolant. That layout cools well and keeps the casting simple, and at stock power it is fine. Add cylinder pressure from a tune, a bigger turbo or a forced-induction kit on a BRZ, FR-S or 86, and the unsupported top of each cylinder has room to move right where the head gasket seals. If you want the full picture of open, semi-closed and closed deck designs, read our explainer Open Deck vs Closed Deck Block.
What are FA20 owners' options?
The traditional routes are a purpose-built closed-deck short block, or a machine shop conversion of your own block. Both work, and both mean tearing the engine down, waiting on shop schedules and paying for machining. For many FA20 projects, especially a street car getting its first real power bump, that is more than the build needs.
EPOXY54 is the DIY alternative: a high-temperature epoxy that fills the top of the water jacket so the cylinder walls are supported, after which the coolant passages are reopened. No deck machining is involved. The product is rated at 21,000 psi compressive strength and is formulated to closely match aluminum's thermal expansion. For how the process converts an open deck to closed-deck strength step by step, see How EPOXY54 Converts Your Open-Deck Aluminum Block to Closed-Deck Strength. It is made in the USA, and every kit ships with full written instructions and an installation video.
Will my FA20 still cool properly?
For a street-driven WRX, BRZ, FR-S or 86, this is usually the deciding question. EPOXY54's Partial Fill configuration keeps OEM coolant capability: once the epoxy cures, the head gasket is used as a template and the coolant passages are drilled back through, so coolant still flows to the head. Our post How Does the Engine Cool After EPOXY54? explains it in detail.
Dry Block fills the jacket completely, with no coolant through the block, and is meant for dedicated drag or track engines. If that is your plan, the Flat 4 Dry Block kit on the product page is 1080 ml, but jacket volume varies by block, so measure your jacket volume first. Still choosing? Partial Fill vs. Dry Block lays out the trade-offs.
Does it cover the rest of the Subaru family?
EPOXY54 lists Subaru EJ and FA/FB series engines among its compatible platforms, so the same approach applies to EJ and FA24 owners looking at the same problem. Running an older turbo Subaru? See our EJ257 closed deck alternative guide. If you are not sure about your exact block or kit size, contact EPOXY54 before ordering.
What else should an FA20 build plan include?
Block support is one part of a reliable boosted engine. Head studs, rod bolts, tuning and cooling all matter too, and the time to plan them is while the engine is apart. Browse our Subaru FA20 collection for the parts that go alongside it.
Planning more power from your FA20? Pick your EPOXY54 kit here: choose Flat 4, then Partial Fill for the street or Dry Block for a dedicated race engine.