In addition to these FAQs, you can also check out our full installation guide, updated August 2017.
What is the total cost of a K series conversion, and how much power will I make?
A competent, DIY enthusiast should be able to do the complete conversion for around $8000. This is only an estimate, as the builder’s choice of K series engine and power goals will determine the final cost. 220whp is realistic with most stock engines with a good tune, and much more power can be made with an upgraded valvetrain and/or a built engine. We already have customers making 300whp N/A with K24 engine builds. Check out our recent dyno testing for more info.
Where can I buy a K series engine?
Since K series engines are very common. Online salvage yard databases can be searched, and we can also source you an engine. Just email us at firstname.lastname@example.org.
Which K series engines are the best for this swap?
This depends on power goals, but we feel the best bang for your buck is a 2006-2008 Acura TSX 2.4L engine (k24a2). There are other great choices, but the TSX engine makes great power in stock form, and provides a great platform for future power upgrades. However, any K series engine (k20 or k24) that is used in FWD Honda swaps can be used in the Miata as well.
What engine management can be used?
We recommend one of three options. KTuner and Hondata Kpro will give you full engine management capabilities. If you're looking for a reflashed ECU for a K24A2 build, we have that too. Check out our new ECU reflash.
Can I use a factory K series ECU, or do I need engine management and a tune?
USDM K series ECUs have immobilizers built in, making them unusable in stock form. You could use a factory 02-04 JDM ECU (no immobilizer), or one of the immobilizer deletes on the market. However, we strongly suggest using full engine management, and getting your setup dyno tuned immediately by a qualified K series tuner. Alternatively, our ECU reflash works well for stock K24A2 swaps.
Does the steering rack need to be moved forward for this swap?
No! The subframe and oil pan setup was specifically designed to maintain the factory Miata steering geometry, unlike many other Miata engine swaps.
How much does the K series weigh compared to the factory Miata engine?
A Miata with A/C and power steering already removed will drop about 30 pounds with this conversion, thanks to the K series being an aluminum block. The additional weight savings is also in part thanks to our new aluminum oil pan. If you begin with a car with A/C and power steering, over 100 pounds is dropped. Weight distribution is exactly 50/50.
What about A/C and power steering?
Most customers have deleted both A/C and power steering. However, our A/C kit is now in stock and available for order. Power steering setups currently require custom work, but we do have a power steering kit in development as well.
Can the factory Miata gauges work with this swap?
Yes, all factory gauges and indicator lights work on the OEM Miata cluster. This was one of the requirements when designing the conversion. The wiring is very straightforward, and the speedometer circuit remains unchanged since the factory Miata trans and VSS are used.
What year Miatas will the subframe, adapter plate, and flywheel fit?
The subframe, adapter plate, and flywheel fit all NA and NB Miatas, 1990-2005. The NB (99-05) front suspension pickup points are used for all subframes, as well as the NB steering rack mounts for improved bumpsteer angle. While the flywheel fits on any K motor, a 1.8L Miata clutch kit must be used.
How are oil pan and hood clearances?
Oil pan clearance is flush with the bottom of the subframe and rest of the chassis, just like a stock Miata. Hood clearance is closer than with a stock engine. a K20 clears fine in either an NA or NB, although some trimming of the hood skeleton is needed for an NA. A K24 clears fine in an NB, but requires the valve cover to be modified to fit under a stock hood. We also recommend this hood from our friends at Treasure Coast Miata. They made a street version with headlight cutouts, as well as the race version to delete headlights.
What Honda parts are needed for the conversion?
At the very least you will need the following OEM Honda/Acura parts: K series engine, K series starter, K series alternator, engine harness and charge harness (either 3002-2006 Element manual trans, or 2002-2004 RSX-S), a K series MAP sensor, and a B series TPS.
Which Miatas come with a Torsen LSD?
We aren’t experts on this, so you are better off consulting this guide: http://www.miata.net/garage/diffguide/ or contacting Mazda directly with your VIN number. They will be able to tell you which options were installed on your car from the factory.
What Honda wiring harness is needed?
If you're using KTuner or our ECU reflash, you'll need a 3002-2006 Honda Element manual engine harness and charge harness. If you're using Hondata Kpro, you'll need the same from a 2002-2004 Acura RSX Type S.
Is a radiator upgrade needed?
It is not needed, but we recommend upgrading to an aluminum 2” radiator core for heavy track use.
What kind of exhaust should I use?
It has been proven time and time again that K series engines breathe best with 3 inch exhaust. Most performance shops can build you a custom stainless exhaust for a similar price of an off-the-shelf exhaust kit. Also, the K swap header will not bolt directly to an aftermarket Miata exhaust, so if you choose to use an existing Miata exhaust kit, it will have to be modified.
How difficult is the wiring for the conversion?
Anyone with a basic understanding of automotive wiring should have no problem wiring the car. Eight wires need to be run from the conversion harness to the under dash Miata harness, and detailed instructions are provided. However, the dash must be removed to perform the necessary wiring. NA Miata wiring is more involved than NB wiring, because the engine harness and dash harness is all one piece. If you'd like to remove the engine harness portion, more care needs to be taken to clean up the unused wiring.