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.
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.
K20K245MT6MTLSDECUVTECBoostDragStreet
01
Choose engine
02
Match gearbox
03
Build the system
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.
| Gearbox | Donor / years | 1st | 2nd | 3rd | 4th | 5th | 6th | Final | LSD | Use |
|---|
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.
Build completion0%
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
Racing & daily builds
DRAG STRIP OR DAILY DRIVER?
A K-swap built to launch hard at the track and a K-swap built to start every morning and cruise the highway are two different engineering problems, even with the same engine code. Decide which one you're building before you buy gearing, a clutch or a cooling system.
Quarter-mile focus
THE DRAG BUILD
Everything is optimized around one number: elapsed time down a fixed distance. Traction off the line and a driveline that survives repeated hard launches matter more than idle quality or highway manners.
→Short, aggressive gearing. A numerically high final drive and a close-ratio box keep the engine near its power peak through every shift instead of falling out of the VTEC band.
→Launch RPM, not idle RPM. Clutch and flywheel choice is built around a repeatable launch — an unsprung or reduced-mass flywheel and a clutch rated well above the engine's torque, not just "streetable."
→Weight comes out, not in. Sound deadening, spare seats and AC hardware are common deletes; every pound removed helps 60-foot times more than most bolt-ons.
→Traction is the real bottleneck. Drag radials or slicks, tire pressure, weight transfer and launch technique usually move ET more than another 20 hp does.
Every-day focus
THE STREET BUILD
The build has to cold-start reliably, idle cleanly, survive stop-and-go heat soak, and be comfortable enough that you actually want to drive it. Peak power matters less than a broad, predictable powerband.
→Tall highway gearing. A lower numerical final drive and a taller top gear keep cruise RPM down, which helps noise, fuel economy and long-term wear.
→Driveability over peak numbers. Factory-style intake/exhaust sizing, a stock-weight flywheel and a well-calibrated idle keep the car pleasant in traffic instead of lumpy and stall-prone.
→Cooling for heat soak. Stop-and-go traffic is harder on cooling than a track pull — a properly bled system, a healthy fan strategy and a clean radiator matter more than peak flow numbers.
→Keep the comfort systems. AC, power steering and sound deadening cost weight but are usually worth it if the car is actually a daily.
Drag build path
GETTING DOWN THE TRACK CLEAN
Gearing for the strip
Pick a final drive and gear spread that keeps the engine in its powerband from launch to the traps. A shorter final drive multiplies torque and shifts more often; a taller one shifts less but can pull the engine out of its best range. Use the gear-ratio tables and speed calculator to check where each gear falls at the trap speed you're targeting.
Launch & 60-foot
The first 60 feet of a pass has an outsized effect on final ET. Consistent launch RPM, smooth clutch or converter engagement, and even weight transfer to the driven wheels matter more than raw horsepower here.
Clutch & flywheel
Match clutch capacity to torque at the wheels, not just crank horsepower, and budget margin for repeated hard launches rather than a single dyno pull. A lighter flywheel revs faster but can make a smooth, consistent launch harder to repeat — pick for the driver, not just the spec sheet.
Tires & traction
Drag radials and slicks behave very differently from a street tire under launch load. Tire pressure, staging technique and suspension setup (or aftermarket traction bars on some chassis) usually gain more ET than the next bolt-on.
Driveline durability
Repeated hard launches are harder on axles, hubs and the transmission than steady street driving. Inspect axle spline condition, differential health and transmission mounts on a car that will see regular track passes, and plan for stronger parts as power climbs.
Safety & tech requirements
Sanctioning bodies (NHRA, IHRA and local tracks) set roll bar, roll cage, harness and parachute requirements tied to elapsed time or trap speed, and these rules change over time. Always confirm the current tech sheet with your specific track before you plan a build around a target ET.
Rule of thumb — verify locally
As a very general pattern, cars running mid-11s or quicker are commonly asked for a roll bar, and cars well into the 9s or quicker are commonly asked for a full cage, arm restraints and other safety equipment — but exact ET/MPH thresholds, required certifications and inspection rules vary by sanctioning body, track and year. Treat this as a reason to check early, not as a rulebook.
Street build path
A K-SWAP YOU CAN DRIVE EVERY DAY
Cruise-friendly gearing
A taller final drive and top gear lower highway RPM, which helps cabin noise, fuel economy and long-term engine wear. Compare final drives in the gearbox table before assuming "6-speed" means the same cruise RPM across every donor.
Cold starts & idle quality
A clean, consistent cold start and a stable idle depend on correct sensor wiring, a proper base calibration and healthy grounds — the same fundamentals that matter for any first start, but under daily scrutiny instead of a one-time track pass.
Heat-soak cooling
Stop-and-go traffic loads the cooling system differently than a track session — low-speed airflow and repeated heat cycles. A properly bled system with a solid fan control strategy matters more day-to-day than outright radiator capacity.
Noise, vibration & harshness
Engine and transmission mount stiffness, exhaust hangers and retained sound deadening all affect how tolerable the car is on a long commute. Race-stiff mounts that feel great at the track can get tiring on rough daily roads.
Emissions & inspection
If the car needs to pass inspection or emissions testing, that constrains engine choice, exhaust and tune decisions from day one. Research your specific region's rules before finalizing a combination — this varies too much to generalize.
Maintenance rhythm
A daily-driven swap needs a normal service interval for oil, coolant and clutch wear items, plus periodic checks of swap-specific parts (mounts, wiring connections, grounds) that a factory car never had.
Quarter-mile estimator
BALLPARK YOUR ET & TRAP SPEED
A classic weight-to-power rule of thumb for a rough estimate — real results depend heavily on traction, gearing, driver skill and the track. Use this to compare builds relative to each other, not as a promised time.
Uses the common ET ≈ 5.825 × (weight ÷ power)^⅓ and trap speed ≈ 234 × (power ÷ weight)^⅓ approximations. Treat the output as a planning estimate, not a guarantee.
The extreme end of the platform
BUILD SPECS & DRAG RECORDS
From stock-sleeve street turbo cars to 5-second, 240+ mph Pro Mods, this is where K-series builds top out — block foundations, extreme spec sheets, and the current fastest K-powered cars on record.
Block foundations
K20 VS. K24: WHAT'S ACTUALLY DIFFERENT
| Dimension | Honda K20 (K20A, K20Z3...) | Honda K24 (K24A2, K24Z7...) |
|---|---|---|
| Deck height | 212 mm | 231.5 mm (19.5 mm taller) |
| Rod length | 139 mm | 152 mm |
| Stroke | 86 mm | 99 mm |
| Bore | 86 mm | 87 mm |
| Rod-to-stroke ratio | 1.62:1 — favors high RPM | 1.54:1 — torque optimized |
| Displacement | 1,998 cc | 2,354 cc |
| Displacement limit (sleeved) | ~2.2L max safe bore | Up to 2.7L with stroker kits |
The K24/K20 hybrid — a tall, high-displacement K24 block topped with a high-flowing, true VTEC K20A or K20A2 head — is one of the most common performance combinations for exactly this reason: K24 torque and displacement under a head built to rev.
Beyond the street build
EXTREME DRAG RACING SPECIFICATIONS
5 & 6-second platforms
1,500+ HP TURBO BUILD
Built to withstand 60+ PSI from large T6-frame turbos (68mm–100mm+) on pure methanol.
→Block: Billet aluminum, or OEM block sleeved with Darton MID or RR rigid ductile-iron sleeves.
→Crank: Ultra-heavy-duty forged or billet steel — often stock 99mm K24 stroke, or de-stroked to 92–95mm for high-RPM stability.
→Rods: Custom GRP solid-beam aluminum, built to absorb combustion shock.
→Pistons: Thick-skirt, low-compression forged (9.0:1–10.0:1) with heavy-wall pins and gas-ported total-seal rings.
→Head: CNC-ported (e.g. 4Piston Pro CNC TSX) with titanium intake valves, Inconel exhaust valves, dual springs and titanium retainers.
→Fueling: Mechanical pump, multiple injectors per cylinder (e.g. 8×2400cc+), standalone FuelTech FT600 or Haltech control.
8-second, no power adders
ALL-MOTOR SPEC
Maximizes volumetric efficiency and airflow velocity to spin safely to 11,500–12,000 RPM naturally aspirated.
→Compression: Extreme 15.0:1–16.5:1 static, with deeply pocketed pistons to clear the valves.
→Displacement: Long-stroke billet cranks (102–106mm) with 90mm overbores for 2.5–2.7L total.
→Rods: Ultra-lightweight custom steel or titanium to cut rotating mass at extreme RPM.
→Induction: 62–67mm individual throttle bodies or forward-facing carbon airboxes into CNC-ported high-velocity ports.
→Valvetrain: Ultra-aggressive high-lift cams with lightweight valve assemblies for 11,000+ RPM lobe ramps.
→Fuel: Specialized oxygenated race fuels — VP M5, Q16 or nitro compounds.
Reliable, pump-gas or E85
400–600 HP STREET / TRACK TURBO BUILD
For road racing, weekend drag events and daily-capable street cars on 93 octane or E85 — the level where a stock-sleeve block is genuinely reliable.
→Block: Stock-sleeve OEM K20 or K24 — reliable to ~600 WHP tuned correctly.
→Pistons: Forged 86.5mm or 87.5mm, 10.0:1–10.5:1 for E85 response.
→Rods: H-beam or I-beam forged steel (Eagle, Manley, BC).
→Valvetrain: Factory VTEC head with upgraded springs and steel retainers — OEM cams often flow well past 500 WHP.
→Head studs: ARP 2000 or upgraded 625+ studs so the head doesn't lift under boost.
→Turbo: Responsive ball-bearing units — Garrett G30-770 or Precision 6266 — on a quality sidemount or top-mount manifold.
→Oil system: K20A2 oil pump swap replaces the restrictive K24 balance-shaft pump for safe revving past 8,500 RPM.
World records
ABSOLUTE FASTEST K-SERIES VEHICLES
World record
Joel Olivo — "No War"
The quickest and fastest K24-powered vehicle in existence.
5.862s @ 243.46 mph
Pro Mod
Pimar Racing
First K-series Pro Mod chassis to crack into the 5-second zone.
5.99s @ 227 mph
RWD tube-chassis
El Judge (Mazda RX-7)
Tube-chassis RX-7 running a Honda K-series engine swap.
6.315s @ 200 mph
RWD tube-chassis
El Diamante
Another rear-wheel-drive tube-chassis drag car built around a K-series.
6.382s @ 215 mph
Leaderboards
AWD & EXTREME FWD RANKINGS
All-Wheel Drive (fastest K-series)
| # | Driver / team | ET | MPH |
|---|---|---|---|
| 1 | Daniel ("Frustrate EG") | 7.14s | 195 |
| 2 | Ostrem Racing | 7.27s | 202 |
| 3 | GP1 Racing (Marc) | 7.27s | 194 |
| 4 | Mateus Racing | 7.39s | 193 |
| 5 | Hiboost | 7.43s | 190 |
| 6 | Carryout Boyz | 7.44s | 198 |
| 7 | Mr. J. Reynolds | 7.45s | 186 |
| 8 | Derf Tuned | 7.47s | 181 |
Extreme Front-Wheel Drive (XFWD)
| # | Driver / team | ET | MPH |
|---|---|---|---|
| 1 | Faster Motorsport | 7.643s | 200 |
| 2 | Chapulin Performance | 7.693s | 188 |
| 3 | Kevin Aleman | 7.716s | 189 |
| 4 | Ramey Racing | 7.759s | 195 |
| 5 | MAR Performance | 7.768s | 196 |
| 6 | Miss Psi | 7.780s | 196 |
| 7 | Natty Racing | 7.782s | 191 |
| 8 | KKT Racing | 7.792s | 188 |
| 9 | Chupatech | 7.819s | 200 |
| 10 | El Chucky | 7.827s | 194 |
No power adders
NATURALLY ASPIRATED (ALL-MOTOR) RECORDS
Absolute class record
Revving to nearly 12,000 RPM with zero forced induction.
8.13s @ 163 mph
Faster Motorsports Civic
Run on a specialized JBR Engines K24 combination.
8.38s @ 168 mph
Carlos ("AllMotorCRX")
On an elite 4Piston engine burning nitro fuel.
8.49s @ 155 mph
All-motor build profile
- Compression: extreme 15:1–16:1 static, vs. 9:1–10:1 in high-boost setups
- Induction: 67mm ITBs or forward-facing carbon airboxes rather than a pressurized manifold
- Drivetrain: lightweight PPG or Quaife sequential gearboxes to keep the motor locked in its narrow, ultra-high-RPM powerband
1,200+ HP turbo build profile
- Block: billet aluminum, or OEM sleeved with Darton MID / RR rigid ductile iron
- Turbo: Precision T6 or Gen 2/3 units, 6870 up to 100+mm, on pure methanol
- Management: standalone FuelTech or Hondata for traction control and complex fueling
Reference rule: drag racing records and leaderboards change constantly as new passes are made. Treat these figures as a snapshot, not a live leaderboard, and verify current standings with the relevant track, sanctioning body or racing organization before citing them as current.
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.
K-Series gallery
SEE THE HARDWARE
Reference photos from Wikimedia Commons. Licensing and attribution are shown with each image.
K20A
Factory K20A presentation
Public domain image by Hatsukari715 / Wikimedia Commons.
HEAD
K20 cylinder head
i-VTEC head reference; Joe Flores / Wikimedia Commons, CC BY-SA 3.0.
CHASSIS
RSX Type-S reference
Matt / Wikimedia Commons, CC BY-SA 2.0.
K24A
K24 long-block reference
Tennen-Gas / Wikimedia Commons. Public domain / GFDL history.
K24W1
Earth Dreams K24W1
Mr.choppers / Wikimedia Commons, CC BY-SA 3.0.
K24V5
Modern K24 family
Nimda01 / Wikimedia Commons, CC BY-SA 4.0.
Images remain subject to their original licenses. KSwaps does not claim ownership. Check the linked Wikimedia Commons file pages before redistributing the images outside this site.
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.
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.
ET
Elapsed time — how long a car takes to cover a fixed drag-strip distance (commonly the quarter mile) from a standing start. The headline number most drag builds are optimized around.
60-foot
The time from the starting line to 60 feet out — a measure of launch quality and traction. A strong 60-foot time usually has a bigger effect on final ET than extra horsepower does.
Trap speed
The car's speed at the end of the measured distance (the traps). A rough indicator of power-to-weight, independent of how well the car launched.
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
Estimated total$0
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