The Miata experience: his and hers.

The engine I bought for my swap is a JDM K24. It's a 3 lobe RBB head engine, so it's basically the same as a K24A2 from an 06-08 TSX, but there are some differences. When I bought the engine, it was the right combination of availability, price, and proximity. I was able to pick it up rather than having it shipped, so overall it was the easy button at the time. That said, I eventually discovered enough differences between the JDM and USDM engines to pretty much wipe out any cost advantage.

For prosperity, these are the USDM parts (Honda/Acura part #s) I ended up using to convert the JDM engine for use in a Miata with the KPower kit:

Water pump housing 19410-RAA-A00
Belt Tensioner 31170-PNA-023
Idler Pulley 31190-RRA-A00
Alternator
Bolt (alt upper) 90025-PNA-000 (M8x1.25 105mm)
Bolt (alt lower) 95701-0805508 (M8x1.25 55mm) x2
Crank Pulley (balancer) 13810-RRA-A02
Crank Pulley bolt 90017-PCX-013

In most cases I just bought new OEM because in my experience the cost difference over used/aftermarket is worth it in track reliability down the road. I used a re-man alternator, and was able to find the alternator bolts at my local hardware (for about the same cost as the Honda parts). The JDM balancer will work, but it's a slightly larger diameter than the USDM part, so it will require a different belt than specified by KPower. Since this is a track car, I figured reducing the accessory speeds could only be a good thing, so I just bought a new balancer.

Please double check any part numbers before ordering... going by my notes. I may also have missed a couple of small parts and didn't include gaskets, etc in the list.

If you are using a mechanical (cable) throttle, and want ECU idle control you will also need an Accord/Element IACV (16022-RAA-A01). This tidbit is buried in the KPower install manual.

Thanks for this info, I have a future project that I plan to use a similar combination of k24a2 & miata driveline, but the info about the k-series in general tends to get mind numbing....

Some more info for posterity...

Since I'm building a new wiring harness, I went with all-new connectors.  Ballenger Motorsports is a great source for this stuff, and below are the part numbers for the K24 connectors:

Crank position sensor - CONN-76246

Cam position/MAP/TPS - CONN-75778

VTC Solenoid/IAT/CLT - CONN-75781

Injector - CONN-75783

Coil - CONN-75784

Alternator - CONN-76257

IACV (Accord/Element for KPower manifold) - CONN-76125

Note that these are "connector kits" with the connector, terminals and seals.  They can also be ordered as pigtails with different part #s.  Ballenger's site is pretty easy to navigate.

USDM balancer compared to JDM balancer:

Now the belt fits, and the accessories will turn a little slower.

My setup for crank bolts...

Thermostat installed, with a block-off for the heater circuit.

Getting closer...

Next project is a heat shield for the trans tunnel.  I stole this from someone else who used a Mazda heat shield from another car and made it fit.  I can't remember which car (CX-5?) at the moment, but the part was cheap on eBay.  It will need some modification, but should work fine.

Last update for today... I bought a set of the Paco Motorsports hub stands to do alignments.  I've been wanting a set for a while, but they're pricey.  FM is now the exclusive seller for these, and they dropped the price pretty significantly so I bought a set.  Between the four cars I can use these for, I expect them to pay for themselves in a couple of years.

One more for today...  Got the heat shield installed.

I used nutserts mounted from the interior side, which gave a nice ~1/4" standoff for the heat shield.  This will leave an air gap between the shielding and the trans tunnel sheet metal.

Initial fit

After trimming and lots of pounding into shape...

I would have preferred more coverage on the driver's side.  I may look into adding another piece of shielding there.

Taken me a week to get thru the entire thread.

Sad I caught up

Start posting more will ya???

excellent work sir, you are an inspiration to the rest of us.

I am facing retirement and you have given me a nudge to start some long postponed projects.

In reply to imarcr2 :

Thanks!

Look at it this way... it took me 7 years to post all that, and you got through it in a week. 

Don't worry, much more to come. 

Today was a relatively small step in the big picture, but it always feels like a big deal.  Motor and trans are joined...

I started with the relief cut in the Mazda transmission bellhousing to clear the Honda starter.

Once I had the location marked and a starter hole drilled, I used a 2" hole saw to make the cut, and then a grinder with sanding wheel to clean up the edges.

Before installation, I cleaned up the inside of the bellhousing, and installed the new t/o bearing.

Once the trans was ready to go, I installed the KPower flywheel, Supermiata clutch and pressure plate and torqued down the adapter plate.

The battle with the transmission was the usual E36 M3 show, and the KPower bolts are just barely long enough to do the job, which made it difficult to get it together by hand to the point where the bolts could be threaded.  Once I got two bolts threaded it went together pretty easily.  Torqued everything down and that was it for today.

The other big event this weekend was a new two-wheeler joined the family.  I have been without a bike since 2021 when I sold my FJ09 Yamaha.  I had always planned to get another after retiring, and after relocating to an area with less inattentive/homicidal drivers.

So last night I brought home a 2007 Honda Interceptor in 25th anniversary Freddie Spencer colors.

That Bike looks great, love the colours!

Is that the same Bike that is known as a VFR800 in other parts of the World?

In reply to Gzwg :

Yes, it is a VFR800.  Honda used the 'Interceptor' name in the US when they introduced the VF500 in 1983, and on the VF750 and VF1000 in the 1980s.  The bikes became 'VFR' s in the 1990s, and Honda brought the 'Interceptor' name back for the 6th Generation VFR in 2002-2009.

My Dad used to borrow a VF500 from his Boss, and do rides with me as a passenger, when I was about 12-16 years old.

Had the same color scheme, so I do have a soft spot for these (but no space at the moment).

Loving the progress and the new bike. 

Before you get the engine installed paint a white line on the harmonic balancer that crosses the rubber insert. This is double extra important if you use the timing marks for anything. Much easier to spot when they start to slip, I've seen too many failures, some that might have been caught.

In reply to TurnerX19 :

Thanks, that's a great tip, will do.

Frustrating day on the Miata today.  Attempted to install the steering rack and inner tie rods.  Discovered I was missing a bolt for the rack.  Also discovered the lock tabs for the inner tie rods that were supplied with the parts don't fit a Miata rack.  The Mazda part is discontinued and NLA.  Great.  

The supplied part was designed for a friction fit, and did not fit over the rack rod.  The Mazda part has two tabs that lock into the rod.  I decided to try modifying one

As supplied on left, modified on right...

The second one came out better...

I'm still not pleased with the outcome, and I later discovered a BMW part that is reported to work as a replacement.  I have some on order.  Stay tuned.

The only real progress is that I got the intake manifold installed.

Since I had to run to the hardware store for a bolt for the steering rack, and I also needed some stuff to finish up the heat shielding in the trans tunnel, and I hadn't ridden my new bike yet,  I decided to take the VFR.

Win #1... after three years, my M/C gear still fits.  

Win #2... I still know how to ride.  It was amazing how quickly all the old habits come back.  Traffic awareness, always maintaining an escape route, etc.

Win #3... the bike is awesome.  I had forgotten how nice these Honda V4s are.  I could take or leave the VTEC, but it was smooth, and sounded great.

I think the idle is a bit high, need to check on that.  The brakes feel a little wooden, so I need to check what it's got for pads, and a fluid flush is probably in order.  Also, the PO installed "FullBore" tires, a brand I'd never even heard of, and they have 2019 date codes.  They were going to go ASAP, but they ride like they're filled with concrete, so tires are first priority.  I ordered a set of Pilot 2CT tires, and a shop manual off eBay.

Other than that, it was nice to be back on two wheels.  I feel whole again. 

My connectors arrived from Ballenger Motorsports, so I went through the order to make sure everything is there, and labeled the bags.

Next up was finishing the trans tunnel heat shielding.  Got a 12x24 piece of aluminum heat shield material off Amazon, trimmed to fit, and riveted on with spacers for a 1/4" air gap.

Next up was 'reconfiguring' the fuel feed and return lines, and the rear brake line.  At least everything is pointing in the right direction now.

Finished the day by pulling the steering rack, shocks and brakes from the original subframe.

The plan is to swap everything onto the new subframe once it's bolted to the engine, then install everything as a unit.

New shoes for the Interceptor are here.

Today started with pulling exhaust studs to gain additional clearance for header R/R.  Those things were tight!

Next up was mounting the subframe to the engine on the hoist.

That was all I had really planned to do today, but I thought... "I'm really close..." and inertia took over...

Next thing I knew, I had the engine on the lift table and under the car...

I planned on taking more pictures, but you know how it is when you get rolling...

Physically bolting the engine into the car is a relative minor step in the big scheme of project... a couple of hours.  But, mentally and emotionally, it's always a BIG deal and feels like major progress.  I am happy to have passed that checkpoint! 

Oh, I forgot to mention...

I hope I never again have to pull a Miata engine out the top!

Installing it from below is SOOO much easier!

More fun stuff for the Interceptor has arrived...  gotta uncork that V4 symphony!

Hopefully I can do the install while the wheels are off for tires next week...