A couple months ago I built a BP05, pushed about 15 psi of boost out of a gt2560r. Loved the car, then my little brother and dad blew up the car….. I’ll spare you all the details but I know have a different Miata, bone stock 95 m edition that I want to throw some power at again and I want to try for more. This is a street car that might end up at the track every once in a while. I was tossing the idea around of doing a k swap (I’m actually going to travel down to Chicago on Sunday and go to an event they are at to get a ride along) and possibly turboing it down the line, otherwise doing another built BP. Although I did see a lot of people complain about NVH in the k swapped cars that scared me off of them a bit. Regardless of what I go with I want to run an 8hp transmission with a turbolamik controller and of course dbw for those smooth cuts and blips.

so my question to all of you, should I do another built BP or go for a k swap and how much power can I realistically make while maintaining enough reliability to not worry about driving the car for an hour or two.

 

From what I remember there are some better options than turbolamik for controlling the 8HP. IIRC Waterson is digging into that swap right now.

My guess is that you're going to have a much easier time finding the parts to mate an 8HP to a K series than a BP. Maybe that's not a big deal for you if you're good at fabricating. How much power can you make reliably? No idea, what's your budget, are you building the engine, what turbo are you using?

IMO if you're set on the 8HP you should start looking at a K swap and putting some money into a high yield savings account.

 

There is an adapter for the 8hp to BP as well as K series. I would love to learn more about better ways to control them, I know that Maxxecu can control them, canTCU and one other that’s horrible but that’s all so far.

 

I have a K swapped track car, and the process and experience has given me a pretty good idea of the realities and capabilities of the swap. IMHO the sweet spot for a K swap is a track car where you want stockish reliability and naturally aspirated ~200-220hp. For that goal, it's perfect, and 220hp makes for a pretty fast Miata that's still reasonably easy on consumables and very fun to drive. Once I got some initial bugs worked out, mine has been reliable (a little over one year in), and I can replace the engine for ~$1500 if it blows. The downsides of the swap are NVH from removing the balance shafts and TIGHT clearances in a lot of spot. From the posts here and elsewhere, pushing rpm past 7500 vastly increases the likelihood of engine problems as does building for big power. I have been happy with the results, but have to be hones that if I were starting again today I'm not certain I would end up with the K24.

For a street car that only visits the track casually, I wouldn't do a K24, especially if you're looking for 250-300hp.

The 8HP transmission is an interesting idea, and at 300hp the additional weight/complexity might be worth it for a track car where you're looking for tenths. For a street car I'd probably just stick with the usual suspects in a manual transmission. Having driven cars with big power and paddles on the street, a manual is more engaging. I have a 6 speed with the K24 and it's very busy on track... I'm probably going back to a 5 speed. More gears is not necessarily better....

 

Sounds like a built BP is the way to go for a street car then. Rip. I was hoping to be able to make really big power in a built k series one day but like you said, NVH makes that hard to bare. Part of my reasoning for wanting to go with a 8hp is I’d like to brake free of the typical 350ish whp limit of the 5/6 speed stock Miata transmissions and make a bit more power. Maybe I’ll regret the auto swap but the lightning fast shifts sound very appealing to me.

 

I'd say it depends. First, NVH is pretty buzzy in the K, but not as bad as I expected after riding in a buddies car. He had 1 rubber 1 poly mount. NVH was buzzy at idle like a full poly mount BP, but definitely did start buzzing pretty hard once the revs got up and became a buzz bomb at 6k+. I thought it was acceptable until I got back into my other buddies N/A BP and felt how damn smooth the thing was. Just cruising around NVH wasn't TERRIBLE though. BP definitely way, way smoother (hard to beat OEM).

If you are targeting much > 400whp, the BP is gonna start to be pretty high strung. Very very possible to make that kinda power (and more), you are just starting to push it hard. Where as the K at that power wouldn't be breaking a sweat, and would be stock internals.

I kinda see the hierarchy as this:

Street car:

Up to 350whp, BP all day. Really easy to make this kinda power and it's a dialed formula. 6 speed will hold it if you keep torque from being too high and show some mechanical empathy, and will probably hold up a long time on street use. I didn't include the N/A K here because NVH, and for street use the turbo BP torque is a clear winner for me.

Above 350whp, especially as you close in on 400+ you need a trans swap as well, which means you might as well jump into a K if you don't mind the NVH. Turbo the K and make allofit. Or build a bulletproof BP, which can take 400+whp, but it aint gonna be cheap. And of course LS swap, which is where I'd go, and maybe what OP should honestly be considering.

Track car:

140-170whp, VVT BP, a bit of compression, optionally cams. Great powerband, fun as hell, really the pinnacle of a miata being a momentum car without too much investment. Basically follow the SPM formula for N/A power and end up with an enjoyable car that you can get a lot of seat time with.

180-240whp, K series gives you a very track friendly N/A powerband. Not a cheap swap, and does come with NVH, but low heat, can stay on stock Miata transmissions, super reliable once dialed, basically OEM honda reliable (or BP reliable with more power). For me this is where the K makes sense, and I would definitely build one for a mostly track build. What a hoot.

200-300WHP. This is the sweet spot for a turbo track BP. Cooling is figured out for this kind of setup, 6 speed should hold if you aren't too ham fisted and keep torque down. Motor doesn't need to be an exotic build, I.E. a rods only rebuild will work fine. Keep the revs fairly low and keep it cool and it'll run for a long time. Recommend e85, oil cooler, reroute, dialed cooling stack and ducting.

350-400whp. Also doable on a BP but starting to lean towards the K swaps favor, mainly because like I mentioned the drivetrain limitations. Often if you are going thru the effort of a drivetrain swap, why would you stop at 400whp? BP's for track abuse are going to be short lived here compared to a K, it's just asking a lot out of the motor and will need a beefy build. Doable on a BP for sure but costs start creeping.

400+. Motor swap it. K with a turbo, sure, but honestly why not go LS?

 

ya i think your right, in a miata, anything more than 350whp requires a trans swap and if your gonna do a trans swap you mind as well swap it all and get something serious (LS or k series), i've been spending a bit of time on kpowers website, and on sunday when i go i will probably investigate the k swapped BRZ and NC, with those chassis, a k swap with balance shaft oil pump retained is possible which seems more streetable. I do like the LS swap na miata but it doesn't feel as true to the nature of the car, maybe I just need to ride in one, idk, maybe someone will convince me one day.

 

IMHO a K swapped NC would be sweet, especially with a turbo, but I don't know that it has any major advantage over a 2.5 swap at a given power level. The additional cost of the swap would cover a nice 2.4 build. The Honda probably has more ultimate power potential, though, either n/a or turbo.

 

I feel like with no budget or power goals this is a much less productive discussion. I'm all for daydreaming, but it's hard to answer a question like this with no real parameters. Fire did a good job breaking it down but this feels like a question you're going to need to think about and answer yourself based on what you actually want out of the car.

 

I EXTENSIVELY researched doing a K-swap for my track NB... There was a litany of reasons not to do it. If you go "oh ill save money over a different swap by re-using the Miata trans and rear end" you'll IMO eventually be in a world of hate when you blow both up as you up the power on the K motor... And once you go down the path of different trans and rear end a lot of the "cost savings" go out the window. The vibrations shaking everything apart even with loc-tite. The high RPM constant abuse on track with no balance shafts WILL lead to blown up engines. The sometimes questionable parts in the k-swap kit and them being the ONLY source... and probably 10 other reasons I decided against it.

For the "same" cost as doing a k-swap with an upgraded trans and rear end you can do an LS swap with 8.8 and T56. LS parts if you scrounge on marketplace can be found cheap. While I already am deep into having a motor built I found a complete L33(aluminum 5.3 with LS1 heads basically) for 800 bucks the other day thats tempting to go pickup. Might need a little work to freshen up and some new seals, an LS2 intake manifold and an oil pan... I dont believe the guys who say you can do an LS swap for 10k bucks, not today, maybe 5 years ago. 15k I think is do-able if you dont go all out on the motor. Im going to be just north of 20k in mine, but im doing a full motor build, brand new trans(t56 Magnum f) and I built my 8.8 rear myself. I scrounged a lot of the motor parts off marketplace(block, heads, crank, rods, intake manifold, etc...).

 

Definitely have a lot of good input and knowledge on this forum regarding swaps/costs/reliability. I would echo fireindc's comments. I think a K "makes sense" if you're going to stay N/A and happy with the low to mid 200whp figure. When I priced it out a year or so ago a K24A2 swap alone would cost ~$12k. I could certainly argue that a turbo BP would also be quite fun and arguably less costly but that's a whole nother discussion. If you're talking about power levels 350whp+ like a turbo K (which also requires a tranny swap/etc), the LS seems like a no brainer imo and the obvious choice. With that said, I haven't driven an LS miata but on paper for the money, reliability wise, etc. It seems like the more sensible choice vs a turbo K. If you poke around in the build threads forum I believe Padlock came to this very conclusion and is going from K -> LS now.

 

Having done a K-swap into my track-only car, I've got lots of thoughts here, but as SimBa pointed out, without some more info from the OP, it's kinda a beers-around-a-campfire discussion.

• What's the goal?
• What's the budget?
• What sort of large projects like this has the OP done before?
  • Fabrication experience
  • ECU experience
  • Wiring experience
  • Troubleshooting experience
• What power levels has the OP actually experienced in a Miata?

The shortest version of my advice is about a K-swap is: it's the right approach for a very specific set of people and goals.

 

- goal is to have a project that I can continue to improve and tinker on while enjoying
-budget is a time thing, longer I wait, more money I have to spend, right now I’ll throw $15-20k at something including the car
-ive built a BP, and was pushing 15-17psi of boost out of a gt2560r, did everything myself
-some fabrication experience but not a ton, I can weld and shape metal good enough for my needs and I can CAD up stuff if I really need to
-my tuning skills are sub par but I’m taking a few HPA classes right now
- I have wired quite a few different projects, this isn’t something that scares me
-I’ve had my fair share of problems I’ve had to troubleshoot my way through
-I’ve had my turbo Miata for a little while now, I’ve ridden in a couple different modified miatas

regarsless I went and talked to kpower over the weekend and I’ll probably end up selling my 95m and buying a blown up brz and k swapping that, supposed to be a better platform for this swap.

 

My car is a bit more of a dedicated track and autocross car, but my built motor just spun a bearing AGAIN. I am done with sending it off to an engine builder to wait around for months without being able to use the car. I am currently working on converting the car to a turbo k24z3. I am looking for around 400whp which the built motor almost did.

I really like the idea of being able to hop in the truck and go pick up an engine the same day for $1200 for a good one.

 

@frostrapper HA! My wife has a 95 M edition that is K swapped that we have tracked for about 2 years. We swapped it after her rotrexed BP gave the ghost.

For the most part it's been pretty dang reliable. My wife uses it as a weekend/nice weather and HPDE car. In terms of NVH, AWR just recently came out with some K24A2 Miata swap mounts that have different durometers. She's using the 70 durometer mounts and they hold the engine well and less buzzy than the K Power poly mounts. There's even a 62 durometer that you might consider to take the NVH down further. I think the 70 durometer felt pretty good personally.

There's a Facebook group for K Swapped Miatas that I'd recommend you check out to see what issues people have run into. But I can share all the challenges we've had with ours if you're interested.

 

No Ecotec love?

 

I wish the guy with the BMW head on the BP block came back and posted results...

 

I'll put this here rather than de-railing your build thread.

Please read my K24Z3 build thread before committing to the K-swap. I think the K24Z swap is not as well-supported as the A2 swap and I think there are some un or under-explored weaknesses to the swap.

I would also advise you to always make sure you buy the V2 version of anything that KPower makes. I have no faith in V1 of anything they produce. If you don't or can't heed this advice, actively watch their website for new product drops, if they create a V2 of something, you should consider upgrading.

I believe there will be new non-KPower engine mounts for the K24Z coming out from a reputable shop at some point in the not-too-distant future. But probably not in time for you to use in your build. In the meantime, if you or Clockwork have decent fab skills, I'd skip the KPower mounts and build your own using off-the-shelf poly bushings with a through-bolt. You need a flat flange on the block side, sealing a couple of oil passages on the ... passenger side I believe. Weld a tube to that, shove the bushings in, then build arms that extend from the subframe to hold the bolt. It's easy for me to generalize this and wave my magic wand to make it sound easy, but it's not rocket surgery.

I strongly advise you to use loctite on everything and Schnorr washers on the intake manifold. I also strongly recommend going with DBW and using the WinningFormula throttle mounting solution over the KPower one. And keep rev limiter below 8000.

I don't know where you're finding K24Z3 motors for $1200 locally, but that's a really good price. Sadly it's over twice what I spent on my original K, delivered to my doorstep.

I guess my overall comment would be, don't go into this believing that the K24Z3 is an easy button with no downsides. It's got merits, but it's not at all "Honda reliability in a Miata shell".

 

Hey there! I will read up into your thread. Great to have some heads up of what I'm getting into.

I wonder if the loctite on the intake is just a skunk2 intake thing? The one I have one the BP seems to like to fall off all the time too. We eventually put self holding nuts on it and that "mostly" worked. Then the studs just liked to back out.

I am working with Penguin Garage who is a dealer for kpower, we will make sure I get the v2 of anything I need. I want to get one of the tubular subframes. Not sure I will have the budget for it right now.

I am certainly not going into it thinking it will be bullet proof. I want it to be cheaper to replace the engines. I beat on them badly. They are not going to last. But, waiting months and months for an engine builder and paying 5 times as much is getting old. I can get them wtth less than 95k miles from a place in Rockford, Illinois. Its not "local" to me as such, but its closer than the racetrack. So, local as far as I'm concerned, lol.

I am curious about the drive by wire. I have this silly thing about the car where I "don't want no nannies!!!!" * insert shaking fist at cloud here * So, I want to do cable.

So you're saying put the rev limiter at 7,999? LOL I am planning on taking it to Andy Smedegard's shop to be tuned. Bronson McNemar from BroFab pointed me in that direction.

 

The cable throttle can vibrate apart as well...



The key is to loctite everything, and keep an eye on everything from event to event.