Subaru FA20 Closed Deck Conversion | BRZ / Toyota 86 / Scion FR-S | EPOXY54
The FA20's Open Deck
Is Why Forced Induction
Builds Fail.
The FA20 is a well-engineered engine held back by one design decision: an open water jacket at deck level that limits how hard you can push it. Turbo kits, superchargers, and big power bolt-ons all hit the same ceiling. EPOXY54 removes it for $159.99.
Order EPOXY54 — $159.99 →A Flat Engine Has Different Structural Challenges Than an Inline.
The FA20's horizontally-opposed layout means the cylinder walls deal with gravitational load differently than a vertical inline-4. An open water jacket at deck level compounds this — and shows up quickly when boost is added.
The FA20 ships with an open-deck design — confirmed by Crawford Performance and documented by aftermarket shortblock manufacturers who specifically offer closed-deck replacements as the solution to the stock block's structural limit.
On a naturally aspirated FA20, the open deck rarely causes problems — the cylinder pressures stay manageable. Once a turbo kit or supercharger is added, the dynamic changes. Cylinder pressure spikes and the unsupported cylinder walls at deck level begin to flex, creating a sealing environment the head gasket wasn't designed for.
Head gasket failure on boosted FA20 builds is the well-documented result — not because the gasket is weak, but because the block moves under it. Closing the deck eliminates that movement.
Why Forced Induction Changes Everything
NA FA20s rarely suffer deck-related failures. Boost changes the pressure environment dramatically — a turbo FA20 at 10 PSI is asking for cylinder seal performance the open-deck block can't reliably deliver.
Aftermarket Shortblocks Confirm the Problem
The existence of a closed-deck FA20 shortblock market (Off The Line Performance, Crawford Performance, Radium) is the clearest evidence the stock block's open deck is a known limitation — manufacturers built an industry around fixing it.
EPOXY54 vs. a Closed-Deck Shortblock
A closed-deck shortblock runs $3,000–$6,000+ before labor. EPOXY54 closes the same deck void in your existing block for $159.99.
Every FA20-Powered Car. Same Block, Same Fix.
The FA20 is shared across multiple badges from two manufacturers. The block is the block — EPOXY54 is applied to the bare engine with the head off, regardless of chassis.
EPOXY54 vs. Closed-Deck Shortblock vs. Block Guard
Three approaches the FA20 forced induction community uses to address the open deck. The cost difference is significant.
| Feature | EPOXY54 | Closed-Deck Shortblock | FA20 Block Guard |
|---|---|---|---|
| Cost | $159.99 | $3,000–$6,000+ (before labor) | ~$150–$250 |
| Deck-Level Structural Support | ✔ 21,000 PSI fill | ✔ Machined closed deck | Partial bore support only |
| Uses Your Existing Block | ✔ | ✘ Full replacement | ✔ |
| Bonds to Block | ✔ Direct epoxy bond | N/A (new block) | ✘ Press fit only |
| OEM Cooling Maintained | ✔ Passages drilled back | ✔ | Restricts inter-bore flow |
| DIY Friendly | ✔ | ✘ Full engine rebuild | ✔ |
| Turnaround | 24 hrs cure | Weeks (build + shipping) | Same day |
Five Steps on a Bare FA20 Block
Engine out, head off. Same process on every FA20 — BRZ, 86, FR-S.
Prep the Block
Fill lower water jacket with a water-soluble temporary solute to hold the fill zone in place.
Mix & Pour
Pour EPOXY54 into the top ¾" of the water jacket around all four cylinders at deck level.
Cure 24 Hours
Room temperature cure — no heat, no press. Cures to 21,000 PSI compressive strength.
Drill Passages
Drill coolant passages back through the cured epoxy per the head gasket layout. Full OEM cooling restored.
Flush & Build
Dissolve and flush the temporary solute. Inspect and proceed with engine assembly.
FA20 Builder Questions
For BRZ, 86, FR-S, and FA20 swap builders adding forced induction.
Your FA20 is Ready
to be Boosted Right.
A turbo kit on an open-deck FA20 is a head gasket failure waiting to happen. Close the deck first, then push it. $159.99, one day of cure time, no machine shop.