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.
K20K245MT6MTLSDECUVTECBoost
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. Because these are all lightweight 1990s-2000s shells (roughly 2,100–2,650 lbs), small weight differences change how much horsepower you actually need.
Performance dynamics
Power-to-weight by chassis
These lightweight-Honda K-swaps live and die by power-to-weight (pounds per horsepower — lower is faster). For reference, a modern Porsche 911 GT3 RS is roughly 5.8 lbs/hp.
| Chassis | Curb weight | ~220 whp | ~350 whp | ~750 whp |
|---|---|---|---|---|
| Civic EG Hatch | ~2,100 lbs | 9.5 lbs/hp | 6.0 lbs/hp | 2.8 lbs/hp |
| Civic EK Hatch | ~2,300 lbs | 10.4 lbs/hp | 6.5 lbs/hp | 3.0 lbs/hp |
| EM1 Coupe / DC2 Integra | ~2,600–2,650 lbs | 12.0 lbs/hp | 7.5 lbs/hp | 3.5 lbs/hp |
| Miata NA/NB (RWD) | ~2,150–2,350 lbs | 10.0 lbs/hp | 5.8 lbs/hp | 2.9 lbs/hp |
Figures are planning-reference estimates from community build data, not measured dyno/scale results for any specific car — actual weight varies with options, interior retained, fuel load and driver weight. Past roughly 400 whp, front-wheel-drive traction on street tires becomes the real limiting factor before power does; many builders budget for a CR-V/Element-based AWD conversion once they plan to cross 500–600 whp.
Giving an EK the EG/DC2 subframe
Popular modThe stock EK subframe pushes the K-series engine farther forward than an EG or DC2 subframe does — tighter radiator/AC clearance, worse axle angles and less header room. Swapping in an EG or DC2 front subframe (with matching lower control arms, steering rack and compliance bushings) is one of the most common upgrades paired with an EK K-swap, and it is not a pure bolt-in — budget the donor hardware and a fresh alignment.
EG subframe
Available in manual (smaller rack tube, narrower D-bracket spacing, ~19.0:1 ratio) or power steering versions. Slightly lighter in manual form. Many base EG models lack front sway-bar mounts.
DC2 subframe
Almost always power steering (wider rack tube/D-bracket spacing, ~16.1:1 ratio — noticeably quicker) and includes proper sway-bar mounts/tabs — the preferred donor if you want a front anti-roll bar.
Mount kit
Use an EKK2-style (or equivalent dual-height) kit built specifically for an EG/DC2 subframe on an EK chassis — not the stock-EK-subframe version of the mounts.
Common pitfall
EK bolts, lower control arms and compliance bushings generally do not fit the EG/DC2 subframe — source the matching donor hardware rather than reusing EK parts, transfer the correct steering rack and D-brackets for manual vs. power, and budget for a professional four-wheel alignment afterward since the suspension geometry has changed.
Wiring & ECU
THE PART THAT STALLS PROJECTS
If a builder gets a single master pin connection wrong, the swap will crank without ever firing. This section covers split-harness logic, the '02–'04 PRB pinout reference, the K20/K24 crank sensor trap, harness sourcing options and ECU choices.
Engine harness
Plug A & Plug B
Routes directly from the K-series fuel injectors, ignition coil packs and block sensors back to the ECU. Handles injector pulse triggers, coil control, VTEC solenoid, and cam/crank sync signals.
Conversion harness
Plug E
Bridges the ECU to the host chassis: gauge cluster, ignition/chassis switches, immobilizer, oil pressure light and the fuel pump main relay.
Rule of thumb
One wrong pin = no fire
Continuity-check every master pin before first crank. Most "cranks but won't start" cases trace back to a ground, a swapped pin, or an unaddressed immobilizer signal.
'02–'04 RSX Type-S (PRB) ECU — key pins
Common failure mode
The K20 harness → K24 crank sensor trap
The K20 harness plug physically clips onto a K24 crank sensor, but the internal pin architecture is different. Plugged in unmodified, the ECU won't read RPM and will throw a sync error, refusing spark and fuel. Re-pin the K20 harness connector to match the K24 sensor before assuming a bad part.
| Pin cavity | K20 harness wire | Target for K24 sensor | Function |
|---|
1. Pop the face-locking cover of the K20 harness connector with a pick tool.
2. Lift the internal plastic retention tabs to back the terminal pins out of the rear wires.
3. Move Yellow/Black → Cavity 1, Blue/White → Cavity 2, Brown/Yellow → Cavity 3.
4. Re-engage the face-locking cover and snap the plug onto the K24 sensor.
Harness sourcing
Plug-and-play vs custom
Pre-made conversion harness (Hasport, Rywire and similar):
Built for a specific engine + chassis combination. Fastest path, least troubleshooting, but least flexible if your donor engine/ECU combo is non-standard.
Tucked / re-pinned OEM harness:
Re-uses the donor engine harness with pins moved to a chassis-specific connector. Cheaper but time-intensive and depends entirely on correct pin mapping.
Fully custom harness:
Built from a pinout sheet for standalone ECUs or heavily modified electronics. Most flexible, most labor, and the least forgiving of documentation mistakes.
ECU options
Factory-based vs standalone
Hondata (KPro / FlashPro):
Works within the factory ECU. Straightforward for factory-supported engine/ECU combinations; less flexible for non-stock sensors or heavily modified fueling.
KTuner:
Similar factory-based tuning approach, commonly used on later drive-by-wire K-series ECUs.
ECU Master / Haltech (standalone):
Full aftermarket ECUs for engines outside factory ECU support, forced induction, or non-stock sensor packages — at the cost of a fully custom wiring and calibration effort.
K20 ↔ K24 wiring specifics
Deep diveMixing K20 and K24 parts is one of the most common swap strategies, but a handful of wiring differences cause the majority of no-starts, RPM faults and random cut-outs. This is what actually matters when the engine, harness and ECU don't all come from the same code.
| Engine | Common ECU | Throttle | Notes |
|---|
Quick rule of thumb
Most "cranks but won't start" problems on K20/K24 mixes come from three places: crank sensor pinout, the immobilizer, or a missing ground/power feed. Check those three before replacing parts.
Pinouts and colors above are a planning reference for the '02–'04 RSX Type-S (PRB) ECU and a common K20→K24 crank sensor mismatch. Always verify against your exact ECU code and donor documentation before cutting or re-pinning a harness — one miswired master pin is the most common reason a fresh K-swap won't fire.
Fuel system
SIZE THE FUEL SYSTEM RIGHT
Injectors and the fuel pressure regulator (FPR) are chosen as a matched pair for your power goal and fuel type — not bought separately at whatever size is on sale. Undersize either one and you'll run out of fuel under boost; oversize it on pump gas and idle quality, mileage and low-RPM control all suffer.
Injectors
Flow match + dead time
Poorly flow-matched budget injectors cause erratic idling and can run one cylinder lean while another runs rich. Premium and exclusive-tier injectors are matched to tight tolerances and ship with full dead-time (latency) data for your ECU.
Regulator (FPR)
Match the pump, not just the injector
A return-style bypass regulator keeps rail pressure rock-solid under load. Pairing a big aftermarket pump with an undersized regulator causes fuel pressure creep — pressure climbing uncontrollably at idle because the regulator can't bypass enough volume.
Rule of thumb
Size for the goal, not "just in case"
Oversized injectors on a mild pump-gas street car struggle to meter tiny pulses of fuel at idle — stumbling, a rich idle and poor mileage. Buy one tier of headroom above your actual power target, not the number you might hit someday.
Injector tiers
Set-of-4 pricing, from budget-conscious street builds up through exclusive, high-end racing tiers.
Fuel pressure regulator tiers
Needed any time you convert to a return-style system or run a high-flow aftermarket pump.
Tuning input
Dead time (injector latency)
Dead time is the delay between the ECU commanding an injector open and it actually flowing fuel — critical for clean idle and part-throttle fueling, and it must be entered correctly into your ECU (KPro, KTuner, Haltech, Hondata, etc.). Lower battery voltage raises dead time; higher fuel pressure raises it slightly too. Always use the datasheet from your specific injectors over a generic value.
| Injector | Approx. dead time | Notes |
|---|---|---|
| Stock K20/K24 (310–350cc) | ~0.8–1.1 ms at 14V | OEM baseline reference |
| RDX 410cc-style | ~0.9–1.3 ms at 14V | Commonly used values — varies by source |
| Bosch EV14-based (DW, FIC, etc.) | Manufacturer datasheet | Usually shipped with full dead-time tables |
| Injector Dynamics (ID1050x/ID1300x) | Manufacturer datasheet | Excellent published data by voltage |
🟢 What's ideal
- Match injector size to fuel type — ID1050x-class injectors are a strong "do-it-all" choice for boosted or E85 builds: enough headroom for real power, but they scale down to a smooth, near-stock idle.
- Bosch EV14-based cores (Injector Dynamics, FIC) give the fastest response and the most precise atomization available.
- Return-style setup with an aftermarket FPR for any K-swap into an EG/EK/DC2 chassis — keeps rail pressure constant regardless of load.
- Alcohol-compatible seals — a Teflon/PTFE or Viton diaphragm (Aeromotive, Fuelab) is a must if you plan to run E85.
- Proper tuning data — ideal injectors ship with a full calibration datasheet so your tuner can enter exact dead times instead of guessing.
🔴 What's not ideal
- Cheap no-name injectors — poorly flow-matched sets can run one cylinder lean and another rich, risking a melted piston.
- Oversized injectors on pump gas — 1300cc+ injectors on a 220 hp N/A street car can't meter small enough pulses, causing stumbling and a rich idle.
- Mismatched pump and regulator — a big pump (Walbro 450/525) paired with a cheap, restrictive regulator causes fuel pressure creep at idle.
- Small injectors under boost or E85 — RDX 410cc injectors are great for cheap N/A builds but hit 100% duty cycle almost immediately under boost.
- FPR mounted far from the rail — long lines between the regulator and rail hurt pressure accuracy; mount it at, or as close as possible to, the end of the fuel rail.
Fuel system by power tier
The right fuel plumbing changes completely as the power target climbs — from a factory-style return system all the way to a full tank-to-rail braided build.
Reference rule: injector sizing, regulator selection and dead-time values above are planning references compiled from community and vendor data. Always verify against your exact injector/regulator datasheets, your ECU's tuning requirements and a wideband O2 sensor before relying on any fuel system at higher power.
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 2.0
DON'T FORGET THE SMALL STUFF
Filter by Street or Track, prioritized Must / Recommended / Nice-to-have. 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
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.
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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.
K20C2
Turbo / direct-injected K
Iamjosemom / Wikimedia Commons, CC BY 4.0.
K24W1
K24 accessory / rear-of-engine view
Mr.choppers / Wikimedia Commons, CC BY-SA 3.0.
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. Have a real build/bay photo to contribute? Email contact@kswaps.com.
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.
Compatibility matrix
ENGINE ↔ TRANSMISSION FIT
Green = straightforward, reference-compatible bellhousing family. Yellow = possible, but needs specific parts, an adapter or extra verification. Red = not recommended as a direct pairing. Tap any cell for what's actually involved.
StraightforwardNeeds specific partsNot recommended
Tap a cell
Select any square in the matrix above to see exactly what a given engine-family / gearbox pairing requires.
Grouped by bellhousing/electronics generation rather than every individual engine code, since bellhousing bolt pattern and input-shaft design — not displacement — is what actually decides a transmission pairing. Always confirm against your exact engine and transmission codes before buying an adapter, flywheel or clutch.
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.
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.
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300×250 Medium Rectangle
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Gearbox picker
Compare a gear instantly
Build budget
Project total (custom)
Estimated total$0
Budget builder
Pick a build tier
Realistic parts-cost ranges by tier, from junkyard-budget to full RWD conversion.
Planning reference only — actual cost depends heavily on core condition, region, whether you DIY labor, and exact parts chosen.
FAQ
Advanced K-Series Engine Lab
BUILD. BOOST. PUSH.
Six connected tools sharing one calculation engine: Easy Mode, Pro geometry/BMEP math, the Frankenstein Builder, Turbo Match, the Build Planner (parts list + cost + build health), and a shared Dyno Database for predicted-vs-actual comparisons.
This tool runs in its own isolated frame with its own calculation engine — open it in a new tab for a full-screen view.
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