K20 Transmission for Sale | OEM Used Honda 6-Speed Manual Transmission Paired with K20 Series Engines

Description

About the K20 Transmission

Looking for a K20 transmission for your Honda or Acura K-series build? You have come to the right place at Part Nests. We offer the Honda 6-speed manual transmission that pairs with K20 series engines, meticulously inspected to ensure quality and performance. Whether you are building a street-legal track-day RSX Type-S, restoring a Civic Si EP3 or FA5, completing an Integra DC5 Type R import, or doing a K-series swap into a project car, we have the right Honda 6-speed manual to fit your K20 engine.

Important Naming Clarification: K20 is an Engine Code, Not a Transmission Code

Before we go further, an important clarification about Honda terminology that helps you buy the right part:

“K20” is Honda engine designation, not a transmission code. Honda K-series engine family (the modern DOHC i-VTEC engines that replaced the legendary B-series engines starting in 2001) includes:

• K20A, JDM Honda Civic Type R (EP3), JDM Integra Type R (DC5), JDM Accord Euro R
• K20A2, USDM Acura RSX Type-S (2002 to 2004)
• K20A3, USDM Acura RSX base (2002 to 2006) and USDM Honda Civic Si EP3 (2002 to 2005)
• K20Z1, USDM Acura RSX Type-S (2005 to 2006)
• K20Z3, USDM Honda Civic Si FA5 / FG2 (2006 to 2011)
• K20C, Honda Civic Type R FK8 (2017 to 2021) and FL5 (2023 plus), the turbocharged variant

When enthusiasts say “K20 transmission,” they typically mean the 6-speed manual transmission that originally came mated to one of these K20 engines. Honda has its own internal codes for these transmissions (M2L4, MFA, etc., depending on application), but the universal shorthand among the K-series tuning community is just “the K20 transmission.” This listing covers that 6-speed manual transmission.

Specific Transmission Identified: 2002 to 2006 RSX Type-S 6MT

Based on the specific gear ratios listed on this product (1st 3.267, 2nd 2.130, 3rd 1.517, 4th 1.147, 5th 0.921, 6th 0.738), this is the close-ratio 6-speed manual transmission used in the 2002 to 2006 Acura RSX Type-S (and its JDM counterpart, the Integra DC5 Type R with the K20A engine).

This transmission signature features:

• Close-ratio gearing designed for high-RPM VTEC operation
• Helical Limited Slip Differential (LSD) factory-equipped on RSX Type-S
• Hydraulic clutch actuation
• 6.4 inch (162mm) ring gear with 4.764:1 final drive ratio (typical RSX-S spec)
• 23-spline input shaft, 25-spline output shaft (CV axles)
• Aluminum case construction, Honda standard for K-series transmissions

This is widely considered one of the best factory front-wheel-drive 6-speed manual transmissions Honda ever produced, the same architecture that won enthusiast accolades in the RSX Type-S and Integra Type R DC5.

K20 Engine Pairing: The Honda Tuner Drivetrain Connection

The Honda K-series 6-speed manual transmission (this listing) is THE matched factory transmission for the K20 engine family in performance applications. For complete Honda K-series drivetrain restoration, this 6MT pairs directly with the K20 engine family in our catalog: the Honda K20Z3 engine (our vaz115 listing, 2.0L Inline-4 DOHC i-VTEC engine with 197 HP at 7,800 RPM and 139 lb-ft at 6,100 RPM, dual-stage intake manifold, drive-by-wire throttle, factory red 8,400 RPM redline, used in the 2006-2011 Honda Civic Si FA5 / FG2 sedan and coupe with factory limited-slip differential and 6-speed manual transmission) is the primary K20 engine application paired with this 6MT in the FA5 / FG2 chassis (though the FA5 / FG2 used a slightly different 6MT with different ratios; this RSX-S transmission can be swapped in with axle and shifter modifications). For broader JDM and Japanese performance engine context across the K20 enthusiast community: the Honda F20C and F22C1 (our vaz144 listing, naturally-aspirated 2.0L and 2.2L DOHC VTEC inline-4 engines for the Honda S2000 AP1 1999-2003 with 9,000 RPM redline and 240 HP, and S2000 AP2 2004-2009 with 8,200 RPM redline and 237 HP) is the contemporary Honda S2000 high-RPM VTEC engine; the Nissan KA24DE (our vaz164 listing, naturally-aspirated 2.4L DOHC inline-4 producing 155 HP and 160 lb-ft, used in the Nissan 240SX S13 1991-1994 and S14 1995-1998) is the Nissan tuner KA-series alternative for drift / swap builds; the Subaru FA20D (our vaz167 listing, naturally-aspirated 2.0L flat-four boxer DOHC engine with direct injection producing 200 HP at 7,000 RPM and 151 lb-ft at 6,400 RPM, used in the Toyota GT86 / Subaru BRZ / Scion FR-S 2013-2020 ZN6 / ZC6 chassis) is the contemporary Toyota / Subaru boxer naturally-aspirated coupe alternative for the affordable RWD enthusiast platform. Multiple JDM and Japanese performance engine families in the tuner space: K20 series per vaz115 K20Z3 the dominant Honda i-VTEC FWD performance engine; F20C / F22C1 per vaz144 the Honda S2000 high-RPM VTEC RWD; KA24DE per vaz164 the Nissan 240SX drift / swap base; FA20D per vaz167 the Toyota / Subaru boxer naturally-aspirated coupe. The Honda K20 transmission (this listing) is specifically the FWD 6-speed manual for the K-series engine family.

Compatibility: Which K20 Engines Does This Transmission Fit

This Honda K-series 6-speed manual transmission is factory compatible with the entire K-series engine family:

Direct Factory Fit (Plug-and-Play):

• K20A (JDM Integra Type R DC5, JDM Civic Type R EP3, JDM Accord Euro R)
• K20A2 (USDM Acura RSX Type-S 2002 to 2004), direct factory match
• K20A3 (USDM Acura RSX base, USDM Civic Si EP3 2002 to 2005)
• K20Z1 (USDM Acura RSX Type-S 2005 to 2006), direct factory match
• K20Z3 (USDM Civic Si FA5 / FG2 2006 to 2011), note: FA5 / FG2 used a slightly different 6MT with different ratios; this RSX-S transmission can be swapped in but requires axle and shifter modifications

K-Series Engines with Adapter Considerations:

• K24A2 / K24Z3 / K24Z7, Honda larger 2.4L K-series engines (Accord, TSX, Civic Si 2012 plus) use a similar but not identical bellhousing pattern; some compatibility with adapter plates and clutch matching
• K20C, the turbocharged Civic Type R K-series engine uses a different (newer-generation) 6MT; the RSX Type-S transmission can be adapted but is not a direct match

NOT Factory Compatible (Different Honda Engine Families):

The following engines have different bellhousing patterns and do NOT factory-fit Honda K-series transmissions without custom adapter plates:

• B-series engines (B16A, B16B, B17A, B18A, B18B, B18C, B20A, B20B, B20Z), these are from the Civic SiR EG / EK, Integra GS-R, Integra Type R DC2, Civic Si EM1, etc. Use B-series 5-speed manual transmissions (Y2, Y80, S40, S80, etc.)
• H-series engines (H22A, H22A4, H23A), these are from the Honda Prelude. Use H-series transmissions (M2A4, M2A5, etc.)
• F-series engines (F20A, F20B, F22A, F22B, F23A), Accord engines. Use F-series transmissions.
• D-series engines (D15B, D16A6, D16Y8, D17A1, D17A2), Honda economy engines in base Civic and Integra LS. Use D-series transmissions (S20, S21, S24, etc.)

B-series, H-series, F-series, and D-series engines use their own dedicated transmissions and are not compatible with K-series 6-speed manuals without custom adapter plates. These adapter plates exist in the aftermarket (e.g., Hasport, Innovative Mounts) for swap builders, but this is an aftermarket modification, not a factory fitment.

Features and Strengths of the Honda K-Series 6-Speed Manual

• Optimized Close-Ratio Gear Set: Designed specifically for high-RPM VTEC engine operation, keeping the K20 in its power band during acceleration
• Helical Limited-Slip Differential (LSD): Factory-equipped on Type-S and Type R variants for improved traction during cornering and launch
• Hydraulic Clutch Actuation: Smoother, more consistent clutch operation than older Honda cable-actuated designs
• Aluminum Case Construction: Lightweight (70 to 80 lbs) for front-wheel-drive weight balance
• Smooth Shifting Synchros: Triple-cone synchros on 1st through 3rd, double-cone on 4th through 6th
• Strong Aftermarket Support: Synchros, gear sets, LSDs, and complete rebuild kits widely available from Honda specialists and the K-series tuning community
• Proven Durability: Stock RSX-S 6MT handles 220 to 240 lb-ft stock; with upgraded synchros and gears can handle 350 plus lb-ft

Common Wear Points to Inspect (K-Series 6MT)

When buying a used K-series 6-speed manual transmission, common wear items include:

• 3rd gear synchro wear, the most common K-series 6MT issue, causes grinding shifts into 3rd
• 4th gear synchro wear, second most common
• Input shaft bearing noise, can develop at high mileage
• Shift fork wear, less common but documented
• LSD wear, in track-driven examples; check for chatter or excessive backlash

Our inspection process specifically checks all of these wear points before any transmission ships.

Vehicle Compatibility

Why Buy From Part Nests

• Application correctly identified by gear ratios and donor vehicle
• Honest naming clarification: K20 is an engine code, not a transmission code
• Compatibility verified: we do not claim factory fit with B-series, H-series, or D-series engines
• All 6 gears shift-tested before shipping
• 3rd and 4th synchro condition documented (common K-series 6MT wear points)
• LSD function verified on Type-S and Type R variants
• Free freight pallet delivery to all 50 states
• 15 day replacement warranty on internal defects
• K-series experienced support team for swap builders and OEM replacement buyers
• Call (855) 634-4447 to confirm Honda K-series 6-speed manual transmission application (RSX Type-S 6MT 2002-2006 close-ratio with helical LSD and 4.764:1 final drive ratio identified by gear ratios 1st 3.267 / 2nd 2.130 / 3rd 1.517 / 4th 1.147 / 5th 0.921 / 6th 0.738, Civic Si FA5 / FG2 6MT 2006-2011 slightly different ratios, or JDM Type R 6MT with K20A engine), donor vehicle (Acura RSX Type-S 2002-2006 direct factory match for K20A2 2002-2004 or K20Z1 2005-2006, Honda Civic Si EP3 2002-2005 with K20A3, Honda Civic Si FA5 / FG2 2006-2011 with K20Z3 engine, JDM Honda Civic Type R EP3 2001-2005 with K20A right-hand-drive markets, JDM Honda Integra Type R DC5 2001-2006 with K20A, Acura TSX 2004-2008 with K24A2 similar K-series family but different variant, or Honda Accord Euro R / JDM Accord with K20A or K24A), all 6 gear shift-test results, 3rd and 4th gear synchro condition (the most common K-series 6MT wear points), input shaft bearing audible noise condition, output shaft and CV axle spline condition, LSD presence and function for Type-S and Type R variants, bellhousing matched to K-series engine bolt pattern, aluminum case condition for cracks, the K20 naming clarification (K20 is Honda ENGINE code NOT transmission code; Honda K-series engine family includes K20A / K20A2 / K20A3 / K20Z1 / K20Z3 / K20C with the universal shorthand ‘K20 transmission’ meaning the 6MT originally paired with one of these K20 engines), the NOT factory compatible Honda engine families to verify (B-series B16 / B17 / B18 / B20 engines use B-series 5MT with different bellhousing, H-series H22 / H23 use H-series transmissions, F-series F20 / F22 / F23 Accord engines use F-series transmissions, D-series D15 / D16 / D17 economy engines use D-series transmissions with different bellhousing patterns; custom adapter plates exist in the aftermarket like Hasport / Innovative Mounts for swap builders but this is an aftermarket modification NOT a factory fitment), and Honda K20 drivetrain pairing context (K20Z3 engine per vaz115 the primary USDM Civic Si FA5 / FG2 K20 engine paired with this 6MT, plus broader JDM and Japanese performance engine alternatives F20C / F22C1 per vaz144 for Honda S2000 high-RPM VTEC RWD, KA24DE per vaz164 for Nissan 240SX drift / swap, FA20D per vaz167 for Toyota GT86 / Subaru BRZ boxer naturally-aspirated coupe) before ordering