VTEC's about to kick in, yo -- my K24 Miata swap is nigh [morning repost]

"MarquetteLa" (marquettela)
07/19/2020 at 09:34 • Filed to: kmiata

Hi Oppo, it’s been a while. In May of last year I finally paid off my credit card debt and so naturally I immediately started saving for a Honda K24 swap for my Miata.

As a refresher, this is the 2002 Miata I bought myself as a college graduation present in 2012. I started entering the totally unmodified car in my local SCCA autocross events and fell in love with performance driving and racing. I’ve put almost 87k miles on it in the years since and have made some modifications to make it a bit quicker on the autocross track. I upgraded to Ohlins Road and Track DFV coilovers as the car’s first modification in August 2014, and followed that up with Flyin’ Miata’s front & rear 4-piston Wilwood Little Big Brake kit in March 2016. Those brakes necessitated upgrading to the 15x8 6UL wheels seen in the photo above. I also installed a MiataRoadster extended, angled short shifter around the same time. In Spring 2019 I added Flyin’ Miata front & rear sway bars and adjustable endlinks. The result is an extremely fun, lightweight, grippy car as you can see in the video below.

So with suspension and brakes pretty well sorted, and myself feeling pretty good about my development as a driver over the past eight years, I figured it’s time to add some more power. Most people in my situation go the forced induction route, but I really like the linear power delivery of naturally aspirated motors. Additionally, people who track their turbo Miatas tend to have a lot of cooling problems. I’m very much interested in having a reliable car I can beat on pretty much all the time. So with these points in mind, I decided to forgo a much more cost-effective turbo in favor of a Honda K24A2 engine swap.

I ordered !!!error: Indecipherable SUB-paragraph formatting!!! back in mid-March. Over the past four months I’ve received a steady stream of packages from Kmiata and other vendors which I’ve been ordering supporting parts from. The very last piece of the puzzle, the Blackbird Fabworx NB GT3 roll bar I ordered in April, finally shipped this week! Now that I have all the parts in, I can actually start picking dates to take off of work to get this project done. The plan is to drive the car from Colorado down to my friend Justin’s place in Tennessee where he’ll help with the swap. He has access to a machine shop for whatever fabrication we might need, and more importantly he has way more experience than I do with this sort of thing. We’ll be doing some other upgrades while we’re at it, too. Here’s a rundown of the major parts for the project:

Ultimate K24 Miata Swap Package w/ race header & flywheel

Kmiata air conditioning kit (turning on air conditioning won’t turn the car into a snail anymore!!)

New A/C parts (condenser, evaporator, compressor)

Hondata Kpro4 for engine management

Hybrid Racing K Series fuel rail

ACT HD clutch kit (my factory clutch is definitely on its way out; perfect timing)

Mishimoto radiator (factory radiator with 129k miles is ready for replacement; perfect timing)

Differential arm reinforcement plates

CarbonMiata radiator panel

Extended stainless steel clutch line

New clutch slave cylinder

3" stainless steel exhaust with Vibrant muffler & resonator, and a G-Sport GESI catalytic converter

Innovate Motorsports MTX-L AFR gauge / MTX-D oil pressure & temperature gauge / MTX-D water temperature & battery voltage gauge

Aluminum steering rack bushings

5X Racing tow hook set

Blackbird Fabworx NB GT3 roll bar

Once I have the car back in Colorado, I’ll be deciding on seats and harnesses. Does anyone have any recommendations on reupholstering racing seats? I really can’t stand the look of black seats in a tan interior like mine. I would order a custom Status racing seat, but they’re too wide to fit well in a Miata.

I’ve seen other people who have done this swap make 220whp and extremely flat torque curves (~160 ft-lbs across the entire rev range as opposed to the Miata’s 100 ft-lbs at redline). I think I’ll be very happy to hit those numbers, as it will be doubling my current power and opening a whole new world of low-end torque. I’m very excited to finally have a sports car that will outrun SUVs and other family cars in a straight line. And with a roll bar, I’ll finally be able to start doing full track events in addition to autocross.

I’m planning to take three weeks off in August to get this done, but hoping to only need about a week and a half.

DISCUSSION (37)

smobgirl > MarquetteLa
07/18/2020 at 22:32

I want my life to be that color green.

I at least need the nail polish version.

(Congrats on the upgrade plan! Sounds like the car is going to be a blast when you’re done)

MarquetteLa > smobgirl
07/18/2020 at 22:37

I literally want every car I ever own to be slathered in this “Emerald Mica” paint. I’ve fallen in love with it. I wish Mazda would paint an Emerald Mica ND Miata, because I bet that would look fantastic.

And thank you! Happy to give rides at the next Coloradoppo meet, whenever that might be lol

Wrong Wheel Drive (41%) > MarquetteLa
07/18/2020 at 22:37

What is your ballpark on total cost for the swap? Or is it “whatever it costs” lol. I love these swaps and kinda wish I could spend that sort of money instead of just doing a vanilla engine rebuild on my Miata. This one is actually a clean car worth doing a swap like this into, although remaining CARB legal is definitely a priority of mine!

What transmision and diff are you running with this swap? Any crazy modifications you are expecting to have to do? Im sure more stuff will creep up and gremlins will persist but this will be so damn cool when complete. Seen plenty of LS swapped miatas and honestly they never seem dialed in quite right. This seems like a much better pairing to me.

MarquetteLa > Wrong Wheel Drive (41%)
07/18/2020 at 22:45

If you’re just doing the swap and not the extra stuff like I’ve mentioned, you can get away with it for around $10k all- in. With my extra upgrades, including the $1,500 roll bar, I’m several thousand beyond that, before seats and harnesses.

The 6-speed Miata transmission and torsen diff my Miata has are the ideal parts to pair with the motor . BMW transmission adapter plates are available if you’re making more than the 300hp the Miata transmission can handle. The biggest aspect of the Kmiata swap is the custom tubular subframe the kit is built around. It necessitates the removal of the power steering system for clearance, so I’ll be depowering my close-ratio steering rack, which from what I hear actually has a very nice feel to it. And I agree, I feel the inline-four is part of the Miata equation, so the more powerful aluminum block K24 is a really great solution for more power in my eyes .

Wrong Wheel Drive (41%) > MarquetteLa
07/18/2020 at 23:19

I'm curious what seats you end up going with. My knockoff bride has seen better days lol. But for what I spent, it has served it's purpose for sure!

RiceRocketeer Extraordinaire > MarquetteLa
07/18/2020 at 23:31

wish I still had a Honda K motor in my life.

MarquetteLa > Wrong Wheel Drive (41%)
07/18/2020 at 23:37

H ow tall are you? I only have a couple inches between my scalp and the soft top. Maybe an extra inch with the hard top on. I’ll probably end up making a trip down to the local race shop and trying out a bunch of seats to see what fits. I imagine I’ll have to essentially mount the seat to the floor to get enough broomstick test clearance.

Wrong Wheel Drive (41%) > MarquetteLa
07/19/2020 at 00:12

Well with the stock seat I have negative clearance to the soft top frame lol. My head is between the frame and the fabric and my hair is a bit crushed if I grow it out at all. At 6'0 I am pretty much max height for a Miata stock. It got wayyyyy better when I put in the garage star mounts with the bride-ish seat touching the floor. Without the seat pads, I have about an inch to the top of my roll bar from the top of my helmet. Crushing myself down with the harness and the padding on the roll bar makes me easily pass a broomstick test at least. But ive seen some organizations that require 2+ inches of clearance. The group I run with wont even question you if you are obviously over the bar so they dont give a fuck haha. But im happy to be within some level of safety at least.

IJustWantMyZBack > MarquetteLa
07/19/2020 at 00:21

2002 Emerald Mica LS owner here, same problem. I want tan racing seats and I need some height clearance . The ones I was looking at are the Co bra N ogaros because you can order them in custom colors/materials. They are supposed to fit well in a Miata. But they are a little pricey. P lan on doing the transmission panel job (I’d get the premade one myself) https://www.cobraseats.com/seats.html?pid=24&cid=3

Nick Has an Exocet > MarquetteLa
07/19/2020 at 00:40

That’s a great swap. I have to say, I keep eyeing it . I just can’t really decide what to do with my Miata. It’s in a weird state. At the very least, my 1.6 motor needs a head and rings. When I did the math on a 1.8 swap (+ 6 speed) , I come to around $5k. That’s a huge amount of money for an engine that isn’t that much more exciting.

I also considered the Ecotec swap but the LE5 is such a garbage throw-away motor that I can’t bring myself to do it. It would be around the same cost as a 1.8 swap ($5-6k).

I’m actually thinking now about rebuilding the 1.6. I also have California smog laws to deal with. Almost all my options (K-swap included) involve some kind of end-around for smog laws. I don’t want to dump too much into the Miata. It’s sort of a daily.

MarquetteLa > IJustWantMyZBack
07/19/2020 at 01:40

Thanks for the suggestion. I would want a seat with 5- or 6-point harness slots, so maybe the Monaco Pro would work better for me.

MarquetteLa > Nick Has an Exocet
07/19/2020 at 01:45

Yeah if I were in your position I would save up a little more and go for a K24Z3 swap , which is about $2k cheaper than the K24A2 swap.

CA smog stuff sounds like a major headache. It should be pretty easy for me to pass CO emissions with the catalytic converter I ordered. Fingers crossed, anyway.

Nick Has an Exocet > MarquetteLa
07/19/2020 at 03:11

I like the idea of the K24Z3 swap. It seems like it might be easier to get a decent motor. I had dismissed it based on cost, but I will have to go back and re-read the swap guide - it may be closer than I realized.

Nick Has an Exocet > Nick Has an Exocet
07/19/2020 at 03:20

Ah, I remember now. It was the oil pump. It has to be swapped/modified to work and they are on backorder to like... october.

MarquetteLa > Nick Has an Exocet
07/19/2020 at 09:32

Bummer. I’d say it’s worth the wait if you can swing it.

CaptDale - is secretly British > MarquetteLa
07/19/2020 at 10:21

Hey that sounds pretty awesome! Should be quite a fun car when you are done. My partner and I keep eyeballing the v6 swap for his NB, but that is something to wait till he is out of school.

About the seats, I have been told an upholstery shop would be the best way to go to make new covers. I really need to recover the Sparcos in my Vette. Honestly I am thinking of just making my own cause fabric is cheap and I feel I could do a good job with it.

MarquetteLa > RiceRocketeer Extraordinaire
07/19/2020 at 10:46

What did you used to have?

IJustWantMyZBack > MarquetteLa
07/19/2020 at 10:54

That makes sense. I was planning on running one of Sc hroths ASM 4 pt belts but I don’t planning on tracking mine as much so I wanted a more street friendly belt.

Schroth

https://www.schroth.com/en/segments/racing/service/technologie-tech-tip/schroth-asm.html

Panel

https://www.miatacage.com/transmission-tunnel-notch-out-panel

MarquetteLa > IJustWantMyZBack
07/19/2020 at 11:45

Yeah, I’ve seen those panels before. I’ll have to see how everything fits under the trans tunnel before committing to something like that.

Wish the Schroth website went into more detail as to how their ASM tech actually works. The roll bar I ordered actually has factory seat belt relocation tabs, so I’ll be able to run the factory belts in addition to a race harness.

Wrong Wheel Drive (41%) > IJustWantMyZBack
07/19/2020 at 12:58

I think a better solution is get rid of all the tan interior bits lol. I've had two NB2s with the tan interior and it just gets so damn dirty. I'm happy the previous owner of this one went with black carpet and most of my pieces for the roll bar came from a black interior car too. So all I have left are the door panels and center console. Little bit of tan is okay but man the fill oem tan is too much for me. I quite like my red seat even if it's faded from never shutting my top.

RacinBob > MarquetteLa
07/19/2020 at 13:38

How far are you from Breckenridge? My buddy who built the TSX and Si I have raced in World Challenge lives down the road from there . He has a wealth of K Motor knowledge and likely spares he’d might sell. For example he might have a trapped oil pan which could be a bonus.

Kinja'd!!!

MarquetteLa > Wrong Wheel Drive (41%)
07/19/2020 at 13:44

I think the tan interior with the green exterior is a really nice combo. Black interiors are over-rated in my opinion.

RacinBob > MarquetteLa
07/19/2020 at 13:46

Here’s an interesting build. It’s sold but you might enjoy the details.

https://www.roadraceautox.com/showthread.php?66052-FS-95-Miata-R-K20-Swap-*Deviate*-(IL)

PS - This guy can get you most anything you need for a Miata. Including probably interiors. http://isellmiataparts.com/

Kinja'd!!!

Wrong Wheel Drive (41%) > MarquetteLa
07/19/2020 at 14:33

I think I’m biased about interior colors a bit though with the blue in the Subaru. That pretty much sold me on that car right away!

RiceRocketeer Extraordinaire > MarquetteLa
07/19/2020 at 14:46

K24 in an Acura TSX, supercharged K20 in an Acura RSX Type-S. The K20 was still going strong at 220k miles when I sold the car.

I have an S2000 and the F22 in it feels crude by comparison - rougher idle, weaker midrange.

This is what we'll show whenever you publish anything on Kinja: > MarquetteLa
07/19/2020 at 15:10

K24A2 weight: 413 lbs

LS1 weight: 430 lbs

Kinja'd!!!

speedyboi > MarquetteLa
07/19/2020 at 15:30

You need a roll bar. Because you’ll be dead without one.

MarquetteLa > RacinBob
07/19/2020 at 16:02

I’m near Boulder. The Kmiata swap requires a very specific oil pan to clear the steering rack:

Kinja'd!!!

Always happy to meet fellow gearheads though!

MarquetteLa > RiceRocketeer Extraordinaire
07/19/2020 at 16:04

A supercharged K20 sounds like a riot.

MarquetteLa > RacinBob
07/19/2020 at 16:06

That’s a really nice build. I’ve bought some parts from Blake before :)

MarquetteLa > This is what we'll show whenever you publish anything on Kinja:
07/19/2020 at 16:07

Now compare their redlines.

MarquetteLa > speedyboi
07/19/2020 at 16:09

Yep, that’s definitely part of the build.

RacinBob > MarquetteLa
07/19/2020 at 16:19

I can send you Brandon’s email address. I hate putting my email on the web, do you have a burner address I can send you his with?

This is what we'll show whenever you publish anything on Kinja: > MarquetteLa
07/19/2020 at 16:45

Can we compare torque curves as well?

MarquetteLa > This is what we'll show whenever you publish anything on Kinja:
07/19/2020 at 17:28

As long as we compare total build costs at the same time.

This is what we'll show whenever you publish anything on Kinja: > MarquetteLa
07/19/2020 at 17:55

We're going to need a bigger spreadsheet.

RiceRocketeer Extraordinaire > MarquetteLa
07/20/2020 at 13:37

It was, but it could never really calm down . The supporting mods made the car harder (stiffer engine mounts, intake/header/exhaust, stronger clutch ) but the throttle response was ... interesting . There’s a vacuum-actuated valve to bypass the s/c when not at full throttle but the resulting situation is that part-throttle is very weak ... then you press the throttle a bit more, the valve closes, and you get an unintentional burnout going down the street. Very on-off switch behavior.

IMO a well tuned natural aspirated K motor is a much more enjoyable setup almost anywhere outside a drag strip .