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.
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.

A real-world K-series engine bay reference. Image: Midship Runabout / Wikimedia Commons, CC BY-SA 4.0.
PICK YOUR K
Start with the exact engine code, then build the supporting system around it.
Rev + response
Great for high-rpm naturally aspirated builds and lightweight chassis.
Torque + displacement
More displacement makes street gearing and midrange power especially attractive.
More electronics
Direct-injected turbo K engines bring different ECU, fuel and integration requirements.
WHERE DOES IT FIT?
A good K-swap plan is engine + gearbox + chassis + electronics, not just an engine purchase.
K-SERIES GEAR RATIOS
Use the exact gearbox code whenever possible. Year and market changes matter.
| Gearbox | Donor / years | 1st | 2nd | 3rd | 4th | 5th | 6th | Final | LSD | Use |
|---|
RSX Type-S 6MT
Click a row to load its gear ladder.
Launch feel, wheelspin and how quickly the engine climbs through the early gears.
Often the most important gears for street pulls, autocross and road-course exits.
Cruising RPM, highway comfort and top-speed potential.
Changes every forward gear. Compare it before assuming two “6-speeds” behave the same.
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.
DON'T FORGET THE SMALL STUFF
Your checklist saves automatically in this browser.
THE SWAP, BROKEN DOWN
Short reference cards for the decisions that usually cause the most rework.
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.
SEE THE HARDWARE
Reference photos from Wikimedia Commons. Licensing and attribution are shown with each image.
Factory K20A presentation
Public domain image by Hatsukari715 / Wikimedia Commons.

K20 cylinder head
i-VTEC head reference; Joe Flores / Wikimedia Commons, CC BY-SA 3.0.

RSX Type-S reference
Matt / Wikimedia Commons, CC BY-SA 2.0.
K24 long-block reference
Tennen-Gas / Wikimedia Commons. Public domain / GFDL history.

Earth Dreams K24W1
Mr.choppers / Wikimedia Commons, CC BY-SA 3.0.

Modern K24 family
Nimda01 / Wikimedia Commons, CC BY-SA 4.0.
COMPARE THE COMBINATION
The fastest way to avoid mismatched parts is to compare the whole powertrain, not isolated components.
K24 + relaxed 6MT
Prioritize midrange torque, comfortable cruise RPM, OEM-like drivability and a sensible final drive.
K20 + close 6MT
Keep the engine in the powerband with a closer spread and aggressive final drive.
Torque + drivetrain margin
Choose gearing, clutch, differential, axles and cooling around the actual torque target—not just horsepower.
Code, head, oiling, sensors, ECU.
Ratios, final drive, differential, code.
Mounts, axles, hubs, clearance.
Fuel, cooling, exhaust, wiring, tune.
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.
K-SWAP LANGUAGE
Quick definitions for the terms you will see while planning a build.
The ratio for one individual gear. A smaller numerical ratio is taller; a larger numerical ratio is shorter.
Limited-slip differential. Helps manage torque distribution between driven wheels when traction differs.
Variable Timing Control. Honda terminology for cam timing control used across many K-series variants.
Honda’s variable valve timing/lift system family. Exact hardware and behavior depend on engine generation and code.
Anti-theft system that can prevent an ECU/engine combination from starting unless the correct key/security strategy is satisfied.
Controller Area Network. Modern Honda systems may use CAN messages for cluster, ECU, ABS and other module communication.
Drive-by-wire electronic throttle. The pedal and throttle body communicate electronically rather than through a mechanical cable.
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.
A conservative starting tune loaded before first start, meant to get the engine running safely — not a finished, optimized calibration.
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.
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.
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.
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.
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.
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.
CALCULATE BEFORE YOU BUY
Planning tools for gearing, tire size and budget.
RPM → MPH
Approximation using tire diameter; real-world speed varies with tire growth, slip and calibration.
Compare a gear instantly
Project total
PLAN THE SWAP BEFORE YOU BUY
Pick the major pieces and generate a starter list.