Mitsubishi 4G63 Closed Deck Conversion | EVO I–IX & Eclipse GSX | EPOXY54

Mitsubishi 4G63 · EVO I–IX · Eclipse GSX · Open-Deck Inline 4

The 4G63 Was Never
Truly Closed Deck.

EVO builders have been closing the 4G63 deck for decades to chase 600+ whp. The professional route is CNC decking or sleeves. EPOXY54 is the weekend solution — $124.99, no machine shop, and no downtime waiting on a shop queue.

Order EPOXY54 — $124.99 →

21,000

PSI Compressive Strength

$124.99

Inline 4 Kit Price

24 hrs

Cure Time

EVO I–IX

All Covered

The Failure Sequence

How a 4G63 Dies Under Boost

The 4G63 is genuinely strong — but the open water jacket at deck level is a structural limit every high-power EVO build eventually meets.

Boost Climbs, Deck Flexes

As peak cylinder pressure rises past 1,000+ psi under boost, the unsupported cylinder walls — sitting above an open water jacket — begin to deflect outward at deck level.

Head Gasket Sees the Movement

The micro-movement at deck level creates a dynamic seal environment the head gasket wasn't designed for. Fire rings begin to take damage before any visible failure appears.

Combustion Gas Escapes

The compromised seal lets combustion gas bypass the head gasket. Coolant temps spike unpredictably. Compression tests start showing variance between cylinders.

The Build Comes Apart

Full head gasket failure, coolant in the combustion chamber, or a hydrolocked engine. On a built 4G63, this means a full teardown of thousands of dollars in parts.

The Fix Is Closing the Deck

Every 4G63 builder doing serious power eventually closes the deck. EPOXY54 fills the void, cures to 21,000 PSI, and restores coolant flow — for $124.99.

Open vs. Closed

What Changes When You Close the Deck

The 4G63's open-deck architecture is the ceiling on every high-boost EVO build. Here's what you're dealing with vs. what EPOXY54 delivers.

⚠ Open Deck — Stock 4G63

What you're working against

Cylinder walls unsupported above the water jacket
Head gasket movement at deck level under high cylinder pressure
Hard power ceiling — serious 4G63 builders close the deck before chasing 500+ whp
CNC closed-deck service: $500–$800+ at a specialist machine shop
Full aftermarket sleeves: $1,500–$2,500+ installed

✔ Closed Deck — EPOXY54

What you get for $124.99

Water jacket void filled and cured to 21,000 PSI compressive strength
Cylinder walls laterally supported at deck level
Coolant passages drilled back — full OEM cooling maintained
No machine shop, no press fit, no weeks of wait time
Works on all 4G63 variants — EVO I through IX, Eclipse GSX

Installation

Five Steps. One Weekend.

Engine out, heads off. The process is the same on every 4G63 — EVO I through IX.

Prep the Block

Fill water jacket with a water-soluble temporary solute to displace the fill zone.

Mix & Pour

Pour EPOXY54 into the top ¾" of the water jacket at deck level around all four cylinders.

Cure 24 hrs

Let it cure fully at room temperature. No heat, no press, no shop visit.

Drill Passages

Drill coolant passages back through the cured epoxy following the head gasket layout.

Flush & Build

Dissolve and flush the temporary solute. Inspect and reassemble.

How It Compares

EPOXY54 vs. CNC Decking vs. Full Sleeves

The three paths 4G63 builders choose between when chasing serious power.

Feature	EPOXY54	CNC Closed-Deck Service	Full Aftermarket Sleeves
Cost	$124.99	$500–$800+ (shop only)	$1,500–$2,500+ installed
Structural Support at Deck	✔ 21,000 PSI	✔ Machined aluminum	✔ Full sleeve support
Machining Required	✔ None	✘ Yes — CNC specialist	✘ Yes — bore & press fit
OEM Cooling Maintained	✔	✔	✔
Thermal Expansion Match	1:1 with aluminum	1:1 (machined from block)	Varies by sleeve material
DIY Friendly	✔	✘ Shop only	✘ Shop only
Turnaround	24 hrs cure	1–3 weeks (shop queue)	2–4 weeks (shop queue)
Works on EVO I–IX	✔	✔	✔

FAQ

4G63 Builder Questions

Straight answers for EVO I–IX and Eclipse GSX builders.

Is the 4G63 actually open-deck? I've seen it called semi-closed. +

The 4G63 has more material bridging the water jacket than a fully open-deck engine like an EJ or K-series, which is why it gets called semi-closed or semi-open depending on who's talking. But the water jacket is still open enough at deck level that high-boost builds routinely exceed its structural limit. Closing the deck — with epoxy, CNC work, or sleeves — is standard practice in the serious EVO community for a reason.

How is the 4G63 different from the 4B11T in the EVO X? +

The 4B11T replaced the 4G63 in the EVO X and shares similar semi-open deck architecture. The 4G63 in EVO I–IX is an older design with a longer stroke, and the aftermarket for it is enormous due to the number of cars on the road. Both blocks benefit from deck closing, and EPOXY54 works on both.

At what power level should I close the deck on a 4G63? +

If you're doing a full internal build targeting 450+ whp, close the deck during the same teardown — it costs you one day of cure time and eliminates the structural ceiling before it becomes a problem. Builders running stock internals at mild boost can often get away without it, but once you're in the block, it's the obvious time to do it right.

Does this work on an Eclipse GSX or other 4G63-powered cars? +

Yes. The 4G63 block is the 4G63 block regardless of the chassis. Eclipse GSX, Galant VR-4, Eagle Talon — any car running a 4G63 benefits from the same process. You're working on the bare block with the head removed, so the car it came out of is irrelevant.

Will EPOXY54 work alongside aftermarket sleeves? +

Yes. If you're running a sleeved 4G63 for overbore or extreme power, EPOXY54 can still be used to fill the water jacket void above the sleeves at deck level, adding the structural deck support the sleeves themselves don't provide.