Mitsubishi 4B11T Closed Deck Conversion — EVO X | EPOXY54
The 4B11T uses a semi-open deck — more supported than a fully open block, but at serious boost levels the unsupported top of the cylinder walls still flex, pulling head gaskets and cracking ring lands. Professional closed-decking services run $700–$1,500+ just for machining. EPOXY54 closes the deck for $124.99, no machine shop needed.
The Semi-Open Deck Problem on the 4B11T
Mitsubishi designed the 4B11T with a semi-open deck — an improvement over fully open designs, but not a solution. The top of each cylinder is still exposed at the water jacket, and that's where failures start on high-boost builds.
Cylinder Wall Movement at High Boost
At elevated boost pressure, combustion forces act laterally on the cylinder walls at the top of the bore — exactly where the 4B11T's water jacket is still open. Wall flex at this point distorts the bore round, breaks head gasket clamping force, and fatigues the ring lands over time.
Professional Closed-Decking Costs $700–$1,500+
Specialist shops offer CNC-machined insert services for the 4B11T — precision bored and press-fit at the deck. It's effective, but between parts, machining, and return shipping the bill climbs fast, often before you've bought a single other component for the build.
EPOXY54 Fills and Supports the Deck
EPOXY54 flows into the open section of the 4B11T water jacket and cures to 21,000 PSI compressive strength — filling the void where cylinder wall movement starts. Coolant passages are drilled back in after cure, so thermal management is preserved.
Budget-Friendly on Any EVO X Build
Whether you're running a hybrid turbo street car or building toward 500+ whp, EPOXY54 lets you address the deck before it becomes an expensive failure — at a cost that leaves budget for the parts that make power.
How to Close-Deck Your 4B11T
Five steps. No press fit. No machinist. Done over a weekend.
Prepare the Block
Fill water jacket with temporary solute like sugar or salt
Mix & Pour Epoxy
Fill top ¾" of block, runny consistency
Cure for 24 Hours
Ready in 24 hours without machining
Drill Coolant Passages
Following head gasket design
Dissolve & Flush
Dissolve solute with water, flush out
EPOXY54 vs. CNC Closed-Decking vs. Full Sleeves
The three main ways EVO X builders address the semi-open deck — side by side.
| Feature | EPOXY54 | CNC Closed-Deck Service | Full Aftermarket Sleeves |
|---|---|---|---|
| Cost | $124.99 | $700–$1,500+ | $2,000–$4,000+ |
| Strength (PSI) | 21,000 | Structural insert | Structural insert |
| OEM Cooling Maintained | ✔ | ✔ | ✔ |
| Machining Required | ✔ None | ✘ Yes — CNC press-fit | ✘ Yes — bore & press |
| Cure / Lead Time | 24 hrs | Days–weeks (shop queue) | Days–weeks (shop queue) |
| Thermal Expansion Match | 1:1 with Aluminum | Varies by insert material | Varies by sleeve material |
| Daily Driveable After | ✔ | ✔ | ✔ |
| DIY Friendly | ✔ | ✘ Shop only | ✘ Shop only |
Common Questions — EVO X 4B11T
Everything you need before you start the pour.
Don't Wait for a Failure
Close-Deck Your EVO X for $124.99 Before It Costs You $4,000
One weekend. No machine shop. Protect your 4B11T block before the next boost spike does the job for you.