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-   -   K swap or build another BP? (https://www.miataturbo.net/engine-performance-56/k-swap-build-another-bp-110461/)

thebeerbaron Aug 1, 2025 05:48 PM


Originally Posted by Timendainum (Post 1668164)
I wonder if the loctite on the intake is just a skunk2 intake thing?

No, the loctite is about the fact that this is a 2.4L engine that has had its balance shafts removed. It'll vibrate bolts loose. Loctite on everything. I specifically mentioned the Schnorr washers on the intake manifold bolts because I've had even loctite-ed bolts back out there. Using these special washers seems to have ended that problem.


Originally Posted by Timendainum (Post 1668164)
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'd hope that KPower is only ever selling their V2 stuff now, this is more of a generalized warning that if they come out with something new, I recommend that you wait a while and buy the follow-up version.


Originally Posted by Timendainum (Post 1668164)
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.

It might be cheaper to be a little more sympathetic to your engines, but you do you boss. :)


Originally Posted by Timendainum (Post 1668164)
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.

DBW isn't a nanny unless you make it a nanny. There's nothing in my Haltech that takes any control away from my throttle pedal. There is probably a table somewhere that maps pedal position to throttle position, so that you can do things like detune to fit a specific power limit, or to give more resolution at lower/higher input percentages, but DBW does not necessarily mean nannies. And sticking cable throttles have been a problem with many K builds.


Originally Posted by Timendainum (Post 1668164)
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.

No, I'm not throwing shade at your tuner or anything, I'm just saying that while the engine can and will rev all the way out there, the last 500-600rpm to reach that pretty number may do more bad (through vibration) than good (in terms of absolute power). If you're going turbo, you probably won't miss those last RPM, spin the motor a little slower and you may experience fewer bolt-shaking-loose issues.

Timendainum Aug 1, 2025 06:38 PM


Originally Posted by thebeerbaron (Post 1668167)
No, the loctite is about the fact that this is a 2.4L engine that has had its balance shafts removed. It'll vibrate bolts loose. Loctite on everything. I specifically mentioned the Schnorr washers on the intake manifold bolts because I've had even loctite-ed bolts back out there. Using these special washers seems to have ended that problem.

Wow, alright! Noted!


Originally Posted by thebeerbaron (Post 1668167)
It might be cheaper to be a little more sympathetic to your engines, but you do you boss. :)

You better watch out, you're starting to sound like my wife. lmao


Originally Posted by thebeerbaron (Post 1668167)
No, I'm not throwing shade at your tuner or anything, I'm just saying that while the engine can and will rev all the way out there, the last 500-600rpm to reach that pretty number may do more bad (through vibration) than good (in terms of absolute power). If you're going turbo, you probably won't miss those last RPM, spin the motor a little slower and you may experience fewer bolt-shaking-loose issues.

Haha! Naw, i wasn't trying to imply anything, just joking. So you're saying keep it to the 7200-7400 range?

rjacobs Aug 1, 2025 08:45 PM

Man 400+ whp sounds like LS time... thats not even any kind of crazy N/A LS either. My destroked LS im building the calculators say I should be just north of 500chp which should net me maybe 425-450 at the wheels...

Or keep putting high strung turbo 4 cyl motors in and wonder why they blow up constantly.

I think if 250whp is the goal a k motor is a great choice... you put a 4 in front of your HP requirements you are going to be constantly trying to keep that same motor together.

Most of the issues on the K swap the other posters are bringing up was a big turn off to me on doing one.

tblackey Aug 8, 2025 01:03 PM


Originally Posted by thebeerbaron (Post 1668167)
No, the loctite is about the fact that this is a 2.4L engine that has had its balance shafts removed. It'll vibrate bolts loose. Loctite on everything. I specifically mentioned the Schnorr washers on the intake manifold bolts because I've had even loctite-ed bolts back out there. Using these special washers seems to have ended that problem.


I'd hope that KPower is only ever selling their V2 stuff now, this is more of a generalized warning that if they come out with something new, I recommend that you wait a while and buy the follow-up version.


It might be cheaper to be a little more sympathetic to your engines, but you do you boss. :)


DBW isn't a nanny unless you make it a nanny. There's nothing in my Haltech that takes any control away from my throttle pedal. There is probably a table somewhere that maps pedal position to throttle position, so that you can do things like detune to fit a specific power limit, or to give more resolution at lower/higher input percentages, but DBW does not necessarily mean nannies. And sticking cable throttles have been a problem with many K builds.


No, I'm not throwing shade at your tuner or anything, I'm just saying that while the engine can and will rev all the way out there, the last 500-600rpm to reach that pretty number may do more bad (through vibration) than good (in terms of absolute power). If you're going turbo, you probably won't miss those last RPM, spin the motor a little slower and you may experience fewer bolt-shaking-loose issues.

So what would your thougths be on the NC version where you keep the balance shafts, off the shelf oil pan, dbw, etc..? with turbo vs an LS? If you were starting out today and had a 400whp target what would you choose? LS adds quite a bit of weight.

rjacobs Aug 8, 2025 01:24 PM


Originally Posted by tblackey (Post 1668402)
LS adds quite a bit of weight.

K motor weighs like 275

BP weighs about 300

Aluminum LS is about 400

Miata 6spd is 90lbs(you arent using a Miata 6spd if 400whp is your goal) which includes bell housing

Tremec TKX is about 100lbs(plus 25ish for bell housing)

If I was doing a k-motor of any flavor I would be looking HEAVILY at the BMW DCT or 8HP70 which are 150-200lbs.

Ford 8.8 rear is like 80lbs

Miata rear is about 65-70lbs


I dont know what a full turbo kit weighs, but guessing 50lbs for everything...

I figure I will be about +150lbs with my LS swap vs. my N/A BP motor/6spd setup. Everybody that has an LS swap I have talked to say the weight is no big deal with the power you are able to make.

400whp with an LS is barely working it at all where as 400whp in a BP or K motor is going to be pushing the internals far harder.

Roda Aug 8, 2025 01:28 PM


Originally Posted by tblackey (Post 1668402)
So what would your thougths be on the NC version where you keep the balance shafts, off the shelf oil pan, dbw, etc..? with turbo vs an LS? If you were starting out today and had a 400whp target what would you choose? LS adds quite a bit of weight.

If 400hp is the goal, I would 100% go LS swap.

Timendainum Aug 12, 2025 02:28 PM

I think it comes down to personal choice.

LS Makes sense for a lot of case. But, its going to change the character of the car. The torque difference from a v8 to a turbo 4cyl are night and day. They are two different cars. I would love to have a LS Miata, but its hard to justify not just buying a corvette in that case.

On the other hand, if you run a k-motor @ 400hp, its gonna blow up occasionally. Something you are going to have to deal with if you want to keep the turbo 4cyl experience.

thebeerbaron Aug 12, 2025 03:14 PM


Originally Posted by tblackey (Post 1668402)
So what would your thougths be on the NC version where you keep the balance shafts, off the shelf oil pan, dbw, etc..? with turbo vs an LS? If you were starting out today and had a 400whp target what would you choose? LS adds quite a bit of weight.

If I was starting out today and had a goal of 400whp, I would choose LS no matter which chassis we're talking about.

I come at this having owned exactly one turbo vehicle in the past, a 2002 WRX wagon that was just the wrong idea at the wrong time for me.

I am also over-exposed to turbo cars that come to HPDE and racing events, often in the hands of people with low mechanical empathy and poor decision making skills. This generally does not go well.

If given the choice to modify an engine to make a particular horsepower goal or to buy an engine that makes the horsepower goal from the factory, I'll choose the factory engine every time.

Since the LS can make 400hp from the factory, without a turbo, I would conclude that it is the right motor.

As far as weight, I think that question has been broken down well above. At 400hp, you're going to need the transmission and differential you'd be using in the LS swap anyhow, so really you're only looking at the difference between the LS and MZR (which I'm seeing as roughly 300lbs). I don't remember what an NC weighs, but let's say the lower-weight motor is 2400lbs and the LS is 2500lbs. That's a 4.1% difference in weight. 100lbs is also approximately 16 gallons of gas.

Basically, I'd throw away the weight "penalty" of the LS. It's probably actually an advantage considering you're going to have 400hp trying to shoot you into orbit.

tblackey Aug 13, 2025 04:14 AM

I'm coming to the same conclusion, not to say the LS will not have it's own issues, but making the power reliably isn't one of them. Oiling is it biggest downside, and there are probably fixes for this, and if not then dry sump will 100% fix it.


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