If you’re planning a rear-wheel drive K24 swap, you know the engine is a legend. But what are the K24 RWD transmission options to get that power to the wheels? This guide breaks down every viable gearbox, from popular OEM choices to custom adapters, giving you the clear facts to make the best decision for your project.
Swapping a K-series Honda engine into a rear-wheel drive chassis is one of the most rewarding projects you can undertake. The K24 offers incredible power potential and reliability. However, the biggest hurdle is always the transmission. Hondas are front-wheel drive, so you need to find a gearbox designed for a longitudinal, RWD layout.
Don’t worry, though. The community has pioneered several excellent solutions. Your choice will depend on your budget, power goals, car’s chassis, and how you plan to use the vehicle.
What Are the K24 RWD Transmission Options
Let’s get straight to the heart of the matter. Your primary options fall into three main categories: adapting a Honda motorcycle transmission, using a modified OEM car transmission from another manufacturer, or going with a purpose-built aftermarket unit. Each has its pros, cons, and specific use cases.
1. The Honda Motorcycle Transmission Route
This is a classic and surprisingly effective solution for lower-power, lightweight builds. The idea is to use a sequential transmission from a large Honda motorcycle, like the CBR600 or CBR1000.
- How it Works: An adapter plate mates the K-series block to the motorcycle gearbox. A custom bellhousing and input shaft are usually required.
- Best For: Ultra-lightweight cars (like Lotus 7 clones, old Minis), track toys, and builds where a tiny, lightweight transmission is critical.
- Power Handling: Generally limited to around 250-300 hp, depending on the specific bike box and how hard you drive it.
- The Drawbacks: They can be less durable under high torque, require a custom shifter setup, and lack a traditional reverse gear (you’ll need a separate electric reverse).
2. BMW Transmission Adaptations
This is arguably the most popular and well-supported path. Certain BMW manual transmissions are strong, relatively affordable, and have readily available adapter kits.
The BMW Getrag 260
This is the budget-friendly entry point. Found in E30 and older E36 325i models, the Getrag 260 is a robust 5-speed.
- Pros: Inexpensive, plentiful in junkyards, and multiple companies make complete adapter kits (K-Miata, KPower Industries, etc.). It fits well in tight engine bays.
- Cons: Not the strongest option. It’s best for near-stock or mildly built K24s, up to maybe 300 lb-ft of torque. Shift feel is notchy.
The BMW ZF 320 & 330
Stepping up in strength, the ZF transmissions from E36 M3s (320) and later E46 models (330) are excellent choices.
- Pros: Much stronger than the Getrag 260, capable of handling 400+ lb-ft with proper treatment. The shift feel is also significantly better. Adapter kits are common.
- Cons: Heavier, larger, and more expensive than the Getrag 260. You need to ensure you get the correct version for your shifter location needs.
3. Toyota (W & R Series) Transmissions
Another legendary transmission family, Toyota’s W-series (like the W58) and R-series (like the R154) are beloved in the drift and JDM community.
- W58 (5-speed): A smooth-shifting but weaker box. Good for stock K24 power levels, but not recommended for big torque. Adapters are available but less common than for BMW boxes.
- R154 (5-speed): The heavy-duty cousin. Found in the Turbo Supra (MK3) and Turbo Soarer, it can handle serious power (500+ lb-ft). It’s a fantastic, albeit increasingly expensive and heavy, option.
4. Nissan CD009 6-Speed
The CD009 from the 350Z/G35 has become a modern superstar for swaps across all engine types, and the K24 is no exception.
- Pros: Extremely strong (handles 700+ hp), relatively affordable, and it’s a 6-speed for better highway cruising. Aftermarket support is huge, with several companies offering complete K24-to-CD009 adapter kits.
- Cons: It’s a physically large and heavy transmission. Shifter placement might be tricky in some chassis. The stock shift feel is a bit rubbery, but short-shifter kits fix that.
5. Aftermarket & Purpose-Built Transmissions
If budget is less of a concern and you want the ultimate solution, look here.
Quaife Sequential or H-Pattern
Quaife offers ultra-high-quality, lightweight transmissions built specifically for swaps like this.
- Pros: Extremely strong, light, compact, and offer perfect shifter placement. The ultimate choice for serious race or high-end builds.
- Cons: The cost is very high, often several times the price of an adapter kit and used OEM transmission.
Holinger and other Racing Transmissions
These are in the realm of professional motorsport. They are incredible pieces of engineering but come with an equally incredible price tag.
Key Components You’ll Need (Beyond the Gearbox)
Remember, the transmission is just one part of the drivetrain puzzle. You’ll also need to source or fabricate:
- Adapter Kit: This includes the bellhousing adapter plate, flywheel, clutch disc, and pressure plate that matches your K24 to your chosen transmission.
- Starter Motor: Your kit will specify which starter to use, often a Honda unit with a custom mounting solution.
- Pilot Bearing/ Bushing: A custom bushing that centers the transmission input shaft in the K24’s crankshaft.
- Driveshaft: A custom, one-piece driveshaft will need to be made to connect your transmission to your car’s differential.
- Shifter & Cables/Linkage: You’ll need to figure out how to connect a shifter to the transmission in your car’s tunnel. This often involves custom fabrication.
- Clutch Hydraulics: You’ll need a master cylinder, slave cylinder, and line that works with your chosen clutch fork and release bearing.
How to Choose the Right Transmission for Your Build
With all these options, making a choice can feel overwhelming. Follow this simple decision tree.
- Step 1: Define Your Power Goals. Be realistic. A stock K24A2 makes about 200 hp. A built, turbocharged one can make 500+ hp. Your transmission must handle your final target torque.
- Step 2: Consider Your Chassis. Measure your engine bay. A massive CD009 won’t fit in a tiny Miata without major surgery, where a Getrag 260 or motorcycle box might slide right in.
- Step 3: Set Your Budget. Factor in the total cost: transmission + adapter kit + clutch/flywheel + driveshaft + shifter solutions. The BMW Getrag 260 route is often the most cost-effective start.
- Step 4: Think About Use Case. Is this a street car, a drift missile, or a dedicated track weapon? A street car benefits from a quiet, smooth-shifting box with an easy reverse. A drift car needs something ultra-durable.
- Step 5: Research Adapter Support. Check which companies make a complete, well-documented kit for your chosen transmission and your specific chassis (e.g., “K24 to BMW Getrag 260 kit for an NA Miata”). Community support is invaluable.
Common Pitfalls to Avoid
Even with a good plan, things can go wrong. Here’s what to watch out for.
- Ignoring Shifter Location: The transmission might fit, but will the shifter come up in the right spot in your car’s interior? Research this before buying.
- Forgetting the Driveshaft: The cost and lead time for a custom aluminum or steel driveshaft can be significant. Plan for it early.
- Clutch Mismatch: Ensure your clutch disc splines match your transmission’s input shaft spline count (e.g., BMWs often use 10-spline, Nissans use 26-spline). Your kit should address this.
- Bellhousing Depth: An incorrect adapter can misalign the clutch, causing disengagement problems or premature wear. Buy from a reputable source.
FAQ Section
What is the cheapest K24 RWD transmission option?
The BMW Getrag 260 is typically the most affordable route. The transmissions are cheap from junkyards, and adapter kits are competitively priced.
What is the strongest transmission for a K24 swap?
For OEM options, the Nissan CD009 and Toyota R154 are extremely strong. For ultimate strength regardless of cost, a purpose-built sequential from Quaife or Holinger is the top tier.
Can you use a K20 transmission for RWD?
No, standard K20 and K24 transmissions are designed for transverse front-wheel drive applications. They cannot be adapted to a rear-wheel drive layout without completely reengineering them, which isn’t practical.
What transmission fits a K24 in a Miata?
The BMW Getrag 260 is the most popular choice for Miatas due to its compact size and excellent aftermarket support from companies like KMiata. The ZF 320 and CD009 can also fit but may require more modification.
Do I need a custom ECU for a K24 RWD swap?
Yes, you will need a standalone engine management system (like Hondata, AEM, or Haltech) to properly run the K24 in a swap, regardless of the transmission. The stock ECU depends on the factory car’s immobilizer and network.
Is a 6-speed better than a 5-speed for a K24 swap?
It depends. A 6-speed (like the CD009) offers closer gear ratios and a better highway cruising RPM. However, 5-speeds (like the BMW units) are often lighter, simpler, cheaper, and have a wider gear spread that can be advantageous for certain performance uses.
Choosing the right transmission is the most critical mechanical decision in your K24 RWD swap. By understanding the options, from the humble BMW Getrag to the mighty CD009, you can match the gearbox to your project’s needs. Start with your power and budget goals, check fitment for your chassis, and invest in a quality adapter kit. With careful planning, you’ll have a reliable and incredibly fun drivetrain that does justice to the legendary K24 engine.