Planning Guide


By popular demand, here's a guide to help you plan out your K swap. We carry most parts that are needed, but feel free to email us at sales@kmiata.com if you need any guidance!

 In addition to this guide, you can also check out our full installation guide.

Engine Selection

For most swaps, we feel the best engine is a K24A2 from a 2004-2008 Acura TSX. However, the 2006-2008 engines are preferred as they are built with stronger internals, and feature larger valves and higher lift cams. Most other 2002-2008 K series engines can be used. Once the necessary Type S oil pump upgrade is done, these engines spin freely to 8000 rpm and are good for around 220whp and 185wtq in stock form with the right supporting bolt-ons and tune.

 

Transmission and Differential Selection

Any NA or NB Miata transmission and differential combo can be used. However, for track use, we recommend going with parts from 1.8L cars (1994-2005). The best combo we have found for road racing, assuming a redline of about 8000 rpm, is a 6 speed transmission with a 4.10 Torsen differential.

 

Basic Swap Components

Every build requires our K Series Conversion Kit. This includes:

  • Subframe
  • Engine mounts
  • Engine/trans adapter plate
  • Flywheel
  • Oil pan
  • Oil pump adapter and pickup
  • Wiring conversion harness

This is enough to get an engine bolted in your car and wired, but additional parts must be selected based on your build goals. (Note: be sure to check out our new Ultimate swap package that includes many of the accessories listed below. It makes your build even more straightforward and cost-effective.)

 

OEM Honda Parts Needed

The following list of OEM Honda parts are either required, or highly recommended:

  • Type S oil pump conversion - we sell it as a full package and include a pump that’s been machined to fit a K24A2 block. There is physically no way to fit any K24 into a Miata without upgrading to this pump. Our oil pump adapter is designed to bolt to this OEM pump.
  • Engine wiring harness and starter harness. Our conversion harness currently supports a 2002-2004 RSX Type S harness from a K20A2, or  2003-2006 Honda Element manual harness. The RSX harness should be used if you're using Hondata Kpro for engine management, and the Element harness should be used if you're using KTuner or the KMiata ECU reflash. Regardless of the harness used, there are several plastic covers that will need to be removed from the harness in order to clean it up and fit it in your RWD vehicle. The plugs for the K series transmission can be removed.
  • Starter - the easiest will be the starter that comes from the same vehicle as your engine harness, but any K series starter can be used. 
  • Alternator - you’ll want to use one specific to your engine (K20 or K24) as the mount is a bit different depending on engine.
  • K series manual transmission flywheel bolts (Automatic bolts are too short)
  • If using a K24, a 50 degree VTC intake cam gear is highly recommended to replace the 25 degree gear. This increases mid-range power significantly, and is easy to install when you replace the oil pump.
  • Timing chain tensioner - we recommend replacing the tensioner when you have everything apart for some preventative maintenance
  • Flywheel dust cover - used to cover up the flywheel behind the oil pan that would be exposed to the elements otherwise.
  • If using an RSX engine harness, a K20A2 knock sensor and crank position sensor are both needed. Alternatively, the K24A2 harness connectors can be cut and spliced onto your K20A2 harness. With the Element harness, no sensor changes are needed.
  • Air/fuel sensor that matches the engine harness you're using. We like the Denso ones that can pick picked up on Amazon, since Denso is an OEM supplier.

 

Intake Setup Choices

You have three main options for your intake manifold (The Ultra Street is standard in the Ultimate Swap package):

  • S2000 - this is the most budget-friendly. You’ll need our manifold adapter, a full S2000 manifold with a throttle body, injectors, and fuel rail, and a manifold gasket.
  • Skunk2 Ultra Street - This is a newer manifold from Skunk2. We have a custom throttle body adapter that allows a B series throttle body to be run on this manifold. It also includes a throttle cable bracket. 

Throttle body:

We recommend the 70mm or 74mm B series throttle body. Depending on the brand, extra water ports may need to be cut off the bottom. A B series TPS is required, and is a much more durable option than the K series sensors that constantly break.

Intake piping:

We recommend 3 inch intake piping. A hole needs to be drilled and a grommet added to fit the OEM intake air temperature sensor. The intake can be routed in a variety of ways, but we recommend getting the filter out of the engine bay if possible.

Extras:

We offer a K series to B series TPS jumper harness. This saves you from cutting up your wiring harness, and extends the length of these wires to the proper length.



Header and Exhaust Choices

We offer two header designs for this swap.  

You can find out more detail about our Street header here and our Race header here. Both headers end with a 3 inch V band flange, so any custom 3 inch exhaust piping can be added after it.

 

Clutch

Any 1.8L Miata clutch can be used. After testing several units, we’re most pleased with the ACT HD Street clutch with organic disc, found in our online store. Others will work as well, but be sure they can hold at least 200wtq. The pilot bearing for your kit will be discarded, as your KMiata flywheel already has a specially-sized bearing installed.

 

Cooling

For either a K24A2 or K20A2 style head, some sort of modified coolant neck is needed. We offer a solution for each type of head. The K24 piece includes a provision for your OEM Miata coolant temperature sender as well.

A K24A2 will also need to have the extra water port on the head blocked off (normally covered by the OEM TSX manifold). This hole can be drilled and tapped with a 90-degree fitting, or you can use the Tractuff coolant reroute for a clean solution. There is lots of info online at k20a.org for different ways to do this.

A K20A2 style head will require the Tractuff coolant neck, and some sort of heater hose reroute. We recommend plugging the OEM heater hose port with a K-Tuned plug, and adding a T fitting under your Tractuff piece to route a line into your heater core.

Heater lines can be made with any ⅝” hose from your local parts store.

Coolant hoses can be made in a variety of ways. While we eventually plan on releasing a full set of hoses, a quality cooling system can be put together with some 1.25” aluminum pipe and some universal silicone 1.25” hose bends. The factory Miata radiator (or similar upgraded unit) can be used. Finally, -16 AN hoses can be used. We supply our upper coolant necks with either a 1.25” or -16 fitting.



Engine Management

A modified ECU is required to run a K series engine in  Miata. A factory ECU cannot work, due to the factory immobilizer. If not using our ECU Reflash, a dyno tune is highly recommended immediately after completing the swap. Email us if you’d like us to supply you with a basemap to get started. Need a tuner near Chicago? We can also help.

The following three ECU options will work for your swap.

1) KMiata K24A2 Reflashed ECU

2) KTuner ECU (full engine management)

3) Hondata Kpro4 (full engine management)

The KMiata reflash and KTuner must be paired with a 2003-2006 Honda Element engine harness, and work with Honda Accord ECUs we keep in stock. Honda Kpro Must be used with a 2002-2004 Acura RSX Type S engine harness, and requires you to send in your ECU to be modified

Be sure to check out each ECU option here. Also, please read our installation guide (page 27) if you have additional wiring and engine management questions.

 

Fuel System

NA Miata (return system):

  • Upgraded fuel pump
  • External fuel pressure regulator
  • Fuel line from regulator to fuel rail
  • Return fuel line from regulator to connect to Miata return line
  • Injectors of your choice (K series 310cc injectors should be fine at 60 psi from the Miata regulator, RDX 410cc injectors can be used if more fuel is needed).

NB Miata (returnless system):

  • Upgraded fuel pump
  • Fuel line from hard line to K series rail
  • Injectors of your choice (K series 310cc injectors should be fine at 60 psi from the Miata regulator, RDX 410cc injectors can be used if more fuel is needed).

Basic rubber fuel injection hose can be used, but most customers prefer to build their setup with -6 AN hoses and an aftermarket fuel rail. We sell the Hybrid Racing rail, but there are many other options on the market.

 

Additional Parts Needed

You’ll need a pulley setup of some sort. We recommend the four pulley setup we sell. The Skunk2 manifold requires you to delete the OEM Honda tensioner, so our kit is a perfect solution. In our experience, the alternator relocator kits on the market will not clear your steering rack with this swap.

 

Additional Parts Needed Specifically for an NA Miata Swap

  • NB steering rack and bottom section of steering column
  • Modified valve cover, a small cut in the hood, or an aftermarket hood like this one
  • More advanced fuel setup, as noted above
  • NB throttle cable. an NA one can be used, but they are usually way too long and don’t work as well in our cable brackets.