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K24 Miata swap... finally a reality

142K views 689 replies 172 participants last post by  Jessedb8 
#1 ·
Okay, I just figured I'd pass this build along to you kiddies. I have nothing to do with this, I am just excited to see it finally being done.

k24 + miata = **** YEAH!

Here is the build
http://www.k20a.org/forum/showthread.php?t=112309

Here is a thread Emilio made cross posting this topic to mt.net.
http://www.miataturbo.net/engine-performance-56/k-series-miata-swap-71588/

Enjoy! Show interest too. More interest = better chance of actually happening. Finally all you N/A fans have another option to spending $7,000 to achieve 160whp lol.

To give you an idea of what a k24 is capable of here is a dyno of a k24a2 out of a TSX with a few simple mods and a stock block. 270whp is pretty friggin awesome.

It is not uncommon for these motors to be making mid-high 300whp when properly built.

http://www.k20a.org/forum/showthread.php?t=71489
 
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#7 ·
I'm just sad there will more than likely be zero chance of making it legal in CA lol. There is no OEM exhaust manifold that will fit this application. Pretty much kills any chance for CA people who need to register it.


As far as the subframe goes, if you read their posts they are planning on developing a tubular subframe. The second car they build will all be bolt on parts.

Depending on swap part prices this swap can be very economical. K24a1s go for ~$800, k24a2s go for ~$1300.
 
#11 ·
As far as the subframe goes, if you read their posts they are planning on developing a tubular subframe. The second car they build will all be bolt on parts.
The guy doing the swap right now is saying that after the prototype car is done, they will be making a tubular subframe like the V8 one to be used in the kits.

Ah, got it. I was mainly looking at pretty pictures
 
#18 ·
Ya i was going to say, you don't necessarily have to use a K24, there is the k20a, a2, and a3 out of the 02-05 civic si. You can find an k20a3 for like $500 for just the motor, but you are only gonna get 160hp, but still more than the stock miata motor. I am going to keep an eye on this and eventually go that route instead of anything else now. Screw cali laws!! lol
 
#194 ·
Re: K24 Miata swap...

It would be nice to see another conversion option, but until the price gets into the $2000 range few people that want it have the means to afford it. That means it's an oddly sized population of people with enough money to do a V8 conversion, but that don't want the V8.

The appeal of a 4cyl swap really is cost and a specific, normally aspirated HP number (greater than 200HP and less than ~250HP). It's someone who wants to have ~200-240 reliable hp all day long from a motor that isn't some rare frankenstein build. Think of all the great driver's cars; E30 M3, E36 M3, NSX, S2000, ITR, GT3RS etc; none of them are boosted and yet, all the real driers who review those cars rave about them. There's a reason.

The only cost savings from doing a 4cyl conversion over doing a V8 is that with a 4cyl conversion you don't have costs associated with changing axles, differential, and band-aid solutions for the PPF or mounting the trans or diff. Fewer things to swap = lower costs and fewer headaches down the road.






There will never be a hybrid swap kit that competes on cost (and performance) with turboing the stock engine. Putting the wrong 4cyl in to a Miata is never going to cost less than ~$8K unless you are the one that can fabricate everything yourself. Cost of motor rarely figures in to the cost of the swap, but no one figures that out until it's time to start the fabrication process.


Newest post is showing the rack is moving forward ~4".
I hope that's not the case. That's really a non-starter for the project.
 
#33 ·
I have one concern about this. The transmission. Assuming all K24 and K20 blocks are the same, there is the potential to bolt in an engine to a Miata transmission that will be seeing 9000 rpm regularly. Can the Miata 5 speed or 6 speed handle consistant high rpm use above the 8000 range? And if it can, doesn't the Miata run of of gear at ~120-130mph? Of course a 5 speed with a 3.9 will net you more top speed, but it's not going to be a lot more I wouldn't think. Other than those potential transmission issues, this could be cool I guess.
 
#34 ·
This seems like the best swap possible right now.

I have one concern about this. The transmission. Assuming all K24 and K20 blocks are the same, there is the potential to bolt in an engine to a Miata transmission that will be seeing 9000 rpm regularly. Can the Miata 5 speed or 6 speed handle consistant high rpm use above the 8000 range? And if it can, doesn't the Miata run of of gear at ~120mph? Of course a 5 speed with a 3.9 will net you more top speed, but it's not going to be a lot more I wouldn't think. Other than those potential transmission issues, this could be cool I guess.
Actually didnt think of that. Good point. Although if kept at stock rev limiter it will be around 8k, I'm sure it would still cause more wear than a regular BP.
 
#35 ·
In addition to my comments, aren't stock Miata transmissions known to grenade around the 250-300whp range? I thought I'd read that about 5 speeds, but I think the 6 speeds can handle a little more right? K series engines can hit that pretty easily, and with roughly the same torque numbers too, which would put a lot of stress on the gearsets and syncros.
 
#38 ·
This is relevant to me. I've been building up a k20/24 hybrid for my project Lotus Europa race car, and I've long toyed with the idea of throwing it into the Miata. But Like Spettro stated, the OEM miata transmission is weak. Now mate it up to an F20 transmission, and you have yourself a good swap.
 
#39 ·
Sounds like a waste of time. "reliable" engine that blows up transmissions, sounds like poop noodle, and a steering rack set up that ruins the steering geometry.

But what does that all matter? CR already fucks up steering geometry and can barely keep the BP running. And why do an engine swap when the weakly goal here is to figure out who stole the parts off your car and figuring out which of the cheapest ebay coil overs will get you the lowest.

just a thought, on here, how many of you have actually been in a miata that is >200 hp or even >250 or 300?

end rant
 
#44 ·
So this could be a bolt in swap, but that requires the addition of custom gearsets or custom rear end ratio to be of use on tracks with long straights. It's certainly a cool project, and I hope it is finished, I'm just not sure that a bolt in K series is the right way to do a K series on a Miata. A K to F transmission with bolt on transmission and differential mounts and a supplied driveshaft seems better, but that drives the cost up a lot too.

Bolting it in as they intend would sure earn you a lot of car show awards and street cred though, but all I care about is the track, hence my voiced concerns. Others may not care about the gearing or transmission reliability issues.
 
#46 ·
^yup (Directed to spettro), another reason why i'd rather go with a v8. once you spend money to get a better transmission/diff (If you ditch the miata transmission) set up, you could of just got a ls_. But your last statement is true. People tend to hate the ls_ motors since people feel that they're overdone or whatever.
 
#49 ·
I'm not an LSx swap fan personally, but I do understand the potentials of the engines and why it is so popular. I'll be building a retro NA for a weekend fun car eventually, and to be honest I don't know if, when the time comes, I'll stick with a BP for it's old school looking 4 cylinder Japanese flavor, or if I'll go the LSx route to do my own version of a 60's looking Japanese Cobra type car.
 
#48 ·
Id bet that the trans would last exactly as long with the k24 as it would with a 250 hp turbo BP. Mechanical empathy will be king with either. a 6 speed will be fine at 250, Id wager. Im not particularly worried about 8k rpm affecting longevity.

a 5speed with a 3.9 final drive goes 155 mph in 5th at 7200 RPM.

a 6speed with same rear end will go 150 at same rpm.

A miata feels extremely hairy over 120mph without significant aero work, in my opinion.



I dont see a problem with the trans. At least not one that we arent already dealing with on the turbo cars.
 
#50 ·
Id bet that the trans would last exactly as long with the k24 as it would with a 250 hp turbo BP. Mechanical empathy will be king with either. a 6 speed will be fine at 250, Id wager. Im not particularly worried about 8k rpm affecting longevity.

a 5speed with a 3.9 final drive goes 155 mph in 5th at 7200 RPM.

a 6speed with same rear end will go 150 at same rpm.

A miata feels extremely hairy over 120mph without significant aero work, in my opinion.



I dont see a problem with the trans. At least not one that we arent already dealing with on the turbo cars.
Thanks for sharing, that's very useful information. But I still wonder about the 8000-9000+ RPM use if a K20 was chosen instead of a K24, or if you simply didn't care about how long the K24 lasted and wanted to push it to 9000RPM.
 
#53 ·
I always assumed if you were going to do a rotary swap you'd use RX7 transmission internals. I remember hearing you can use something like an S4 or S5 FC bellhousing on a Miata transmission case with FC internals, but I could be remembering incorrectly, this was a while ago and was by word of mouth, I didn't read it somewhere.
 
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