K-Series swap reference

BUILD
THE K.
RIGHT.

Engine codes. Transmission ratios. Chassis fitment. Wiring. Fuel. Cooling. ECU. Calculators. Checklists. Everything organized around the actual decisions that make a K-swap work.

K20K245MT6MTLSDECUVTECBoost
01
Choose engine
02
Match gearbox
03
Build the system
Honda K20Z3 engine installed in a Civic Si
Featured platform
K20Z3 / K-SWAP

A real-world K-series engine bay reference. Image: Midship Runabout / Wikimedia Commons, CC BY-SA 4.0.

Engine database

PICK YOUR K

Start with the exact engine code, then build the supporting system around it.

K20 mindset

Rev + response

Great for high-rpm naturally aspirated builds and lightweight chassis.

K24 mindset

Torque + displacement

More displacement makes street gearing and midrange power especially attractive.

Modern K

More electronics

Direct-injected turbo K engines bring different ECU, fuel and integration requirements.

Reference rule: horsepower, compression, VTEC configuration, oiling, sensors and ECU strategy vary by exact engine code, market and year. Verify the long block and donor documentation before buying parts.
Chassis guide

WHERE DOES IT FIT?

A good K-swap plan is engine + gearbox + chassis + electronics, not just an engine purchase.

Gearbox database

K-SERIES GEAR RATIOS

Use the exact gearbox code whenever possible. Year and market changes matter.

Why final drive matters:a higher numerical final drive multiplies torque at the wheels and raises RPM at a given road speed.
GearboxDonor / years1st2nd3rd4th5th6thFinalLSDUse
Quick comparison

RSX Type-S 6MT

Click a row to load its gear ladder.

What to compare
1st–2nd:

Launch feel, wheelspin and how quickly the engine climbs through the early gears.

3rd–4th:

Often the most important gears for street pulls, autocross and road-course exits.

5th–6th:

Cruising RPM, highway comfort and top-speed potential.

Final drive:

Changes every forward gear. Compare it before assuming two “6-speeds” behave the same.

Ratio references are compiled from Honda/Acura specification material and long-standing transmission references; some online references disagree on individual codes. Treat this table as a planning reference and verify the stamped transmission code/service documentation before ordering gears or differentials.
Reference specs

TORQUE & FLUIDS

General sanity-check ranges for common K-series fasteners and service items. These are typical values seen across the K-series family, not a substitute for the factory service manual for your exact engine code.

Reference rule: exact torque specs, fluid types and capacities vary by engine code, transmission code and model year. Always confirm against the applicable factory service manual, especially for head bolts, connecting rod bolts and any fastener that affects safety.
Parts checklist

DON'T FORGET THE SMALL STUFF

Your checklist saves automatically in this browser.

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Guides

THE SWAP, BROKEN DOWN

Short reference cards for the decisions that usually cause the most rework.

First-start checklist
□ Compression / leak-down checked
□ Oil + filter serviced
□ Timing / VTC inspected
□ Grounds cleaned
□ Fuel pressure verified
□ Cooling system pressure-tested
□ Wiring continuity checked
□ Fluids filled correctly
□ ECU base calibration loaded
Diagnostics

SOMETHING'S WRONG — START HERE

Common post-swap symptoms, likely causes and a sensible order to check them in. Tap a symptom to expand it.

Reference rule: this is a starting checklist, not a full diagnostic manual. Work through causes from simplest/cheapest to most invasive, and stop if you smell fuel, see smoke, or suspect a safety issue.
Decision center

COMPARE THE COMBINATION

The fastest way to avoid mismatched parts is to compare the whole powertrain, not isolated components.

Street

K24 + relaxed 6MT

Prioritize midrange torque, comfortable cruise RPM, OEM-like drivability and a sensible final drive.

✓ K24 torque
✓ Taller highway gearing
✓ Strong daily-driver layout
Track / NA

K20 + close 6MT

Keep the engine in the powerband with a closer spread and aggressive final drive.

✓ High-rpm character
✓ Shorter shifts between gears
✓ Strong road-course fit
Boost

Torque + drivetrain margin

Choose gearing, clutch, differential, axles and cooling around the actual torque target—not just horsepower.

✓ Plan wheel torque
✓ Upgrade clutch / LSD as needed
✓ Monitor heat and traction
Powertrain checklist
Engine

Code, head, oiling, sensors, ECU.

Gearbox

Ratios, final drive, differential, code.

Chassis

Mounts, axles, hubs, clearance.

Support

Fuel, cooling, exhaust, wiring, tune.

Technical note

A gearbox that looks “better” on paper can be worse for your build if its final drive, clutch interface, shifter arrangement, axle spline, differential or speed-sensor strategy does not match the chassis.

Reference glossary

K-SWAP LANGUAGE

Quick definitions for the terms you will see while planning a build.

Final drive

The ring-and-pinion ratio multiplying every forward gear. Higher numerical values generally raise RPM at a given road speed and increase wheel torque multiplication.

Gear ratio

The ratio for one individual gear. A smaller numerical ratio is taller; a larger numerical ratio is shorter.

LSD

Limited-slip differential. Helps manage torque distribution between driven wheels when traction differs.

VTC

Variable Timing Control. Honda terminology for cam timing control used across many K-series variants.

i-VTEC

Honda’s variable valve timing/lift system family. Exact hardware and behavior depend on engine generation and code.

Immobilizer

Anti-theft system that can prevent an ECU/engine combination from starting unless the correct key/security strategy is satisfied.

CAN

Controller Area Network. Modern Honda systems may use CAN messages for cluster, ECU, ABS and other module communication.

DBW

Drive-by-wire electronic throttle. The pedal and throttle body communicate electronically rather than through a mechanical cable.

Intermediate shaft

A short connecting shaft used on some chassis/transmission combinations to link the transmission output to one of the axles when lengths or offsets don't match directly.

Base ECU calibration

A conservative starting tune loaded before first start, meant to get the engine running safely — not a finished, optimized calibration.

Main relay

A relay that supplies power to the ECU and fuel system. A failed or miswired main relay is a common no-start cause after a swap.

Rod bearing / journal bearing

The bearing surface between the connecting rod and crankshaft journal. Bearing condition and clearances matter when evaluating a used core, especially a high-mileage or unknown-history one.

OBD1 / OBD2 / OBD2b

On-board diagnostics generations used across Honda ECUs and model years. The generation affects connector pinout, diagnostic tools and which ECUs are electrically/programmatically compatible.

Big block / small block

Community shorthand distinguishing K24-based blocks (“big block”) from K20-based blocks (“small block”) by physical case size, independent of the specific head or tune.

Swap kit

A packaged set of mounts, brackets and sometimes axles/wiring adapters designed for a specific engine-to-chassis combination. Kit scope varies a lot between vendors — confirm exactly what's included.

Rule of thumb

Whenever a forum post says “all K-series parts are interchangeable,” stop and identify the exact engine code, transmission code, year, market and chassis. That is where most compatibility mistakes start.

Build tools

CALCULATE BEFORE YOU BUY

Planning tools for gearing, tire size and budget.

Speed calculator

RPM → MPH

— mph

Approximation using tire diameter; real-world speed varies with tire growth, slip and calibration.

Gearbox picker

Compare a gear instantly

Build budget

Project total

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FAQ
Build planner

PLAN THE SWAP BEFORE YOU BUY

Pick the major pieces and generate a starter list.

DATABASE
ENGINES + CODES
GEARING
RATIOS + FINAL DRIVES
FABRICATION
MOUNTS + CLEARANCE
ELECTRONICS
ECU + WIRING