Yeah, limiting the motor to a sub-7k redline is the plan. Most guys seem to be revving the 2.5s out to 7,200 (same as the current redline on my 2.0), but I'd rather sacrifice a few hundred rpm to keep the engine alive longer. You're very right about the cam profiles in these things too, the powerband in a stock 2.5 peaks really low and they're out of breath well before redline. I'm gonna go with a set of hotter cams on my build, but nothing aggressive enough to require upgrading springs.

Way down the line, maybe I'll build a hot motor for this thing some day. A popular upgrade is to swap the crank out of a 2.3L EcoBoost motor which destrokes the 2.5 to a 2.4 (and then obviously upgrade some bottom end stuff while you're in there).

Edit: As if on command, a dyno plot for a non-cammed 2.5L popped up on the ol' BookFace feed this morning. You can see how hard torque falls off at high-rpm.
https://cimg3.ibsrv.net/gimg/www.mia...7c250574b3.png

o man it drops like a rock after 5250 eh. adding another 500-800rpm would be nice

Yeah dude, peak torque at 3,200rpm is probably suboptimal for a track car haha.

Multiple exciting things happening today.

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Awe yisssssss xidas bby! 2.5 looks clean too

Haha yessir! So amped to finally have a top-end set of coilovers on a car I own. I think the BC coilovers on my NA were the weakest link in an otherwise pretty strong setup and wanted to make sure I had that base covered on this build.

Ed and I chatted spring rates for the Xidas earlier this week and it basically came down to my current setup favoring 11/7k rates, but my future setup (más tire, power & aero) favoring 16/9k spring rates. Since I’m hoping to keep this project moving, and want to take an extra step (and a few hundred bucks) out of the process by changing spring rates later, we went with the 16/9k rates for my setup. Definitely oversprung for now, but will still be a huge step up from my 7k/5k Teins. I only got to install the rears yesterday. They’re way stiffer, but still somehow more compliant over bumps than the Teins.

The 2.5 spins freely by hand so that’s a good sign. Still gotta leakdown test it.

I did a leakdown test on the 2.5L motor today and got 20-50% leakage from all of the exhaust valves. There was a bunch of carbon buildup in the exhaust ports though, so I filled them up with sea foam for a bit then blasted them out with brake clean and compressed air. Rotated the engine over a couple more times and cylinders 3 and 4 sealed up with less than 20% leakage. Cylinders 1 and 2 improved but were now leaking from the intake valves instead of the exhaust valves. Based on this, I’m assuming the leakage is due to the carbon buildup. Im gonna sea foam the ports and valves again and try to clean as much up as possible. Anyone have a similar experience with this? This is my first time leakdown testing a used engine that’s likely been sitting for a while. Should’ve taken some pics of the ports but I’m out of town now and won’t be back till Monday.

Xidas are installed. Look at all that droop! I set ride heights to 4.75” front, 5” rear. SM recommends a tad higher, think I’m gonna raise the car a quarter inch next week then give ‘er an alignment. I set the front sway to full soft as well. Gonna do the same with the rear.


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Jesus, I forgot I needed to clean up my passenger side fender cut somehow

https://cimg5.ibsrv.net/gimg/www.mia...7f08038e1.jpeg

Lmao at that passenger fender cut. When you don't see that side of the car often it's easy to forget that stuff.

Interesting oil filter placement on the 2.5, I assume it's easy to service in that location?

Excited to see what you think of the Xidas coming from the BCs.

Z, I assume this is you after this update

Re:leakdown, I've never gotten good results from cold/sitting motors doing a leakdown. Even on perfectly good motors that sealed up once running (and leakdown test was re-done hot). I personally don't have much faith in a cold leakdown test other than finding catastrophic failures.

Holy droop batman, the xida looks sexxx. That fender is mangled bruh. Maybe do a vertical cut right where it folds, and replace it with a sheet of ABS plastic or similar riveted to it, and riv-nutted bolted to the body. I bet you could make it look pretty nice ala garbage can bumper style.

Yeah dude, luckily it's not super visible with the car on the ground and wheels on, otherwise I'd be even more embarassed hahaha.

Yeah, the oil filter perch is in the same location on the 2.0 and 2.5L. Not too hard to get to with the engine in the car. I have to remove one small x brace under the bell housing to get to the oil filter but that's it. No big deal.

I appreciate the Donald Glover reference bigtime hahaha. Yeah, I spent way more dollars than I should have last week but luckily I cashed out really well parting out the NA and am still riding that wave. If it weren't for that, I'd be going way slower with this build haha.

Super amped on the droooooop! Can't wait to see how they perform on track. Waaaay more travel than my Teins haha.

Dude, that's actually a super sick idea for the fenders. Maybe I'll mock something up like that in the coming weeks. I'm considering making an NA/NB-style ABS air dam for this car at some point so the ABS fender inserts might not look too out of place if I do both of those at once. Only seen one NC with an air dam before but it's so ugly that I kinda like it...

Got plenty of things/updates with the car but figured I'd take a quick detour with the engine update today. I appreciate your guys' input re: doing a leakdown test on a cold engine that's been sitting for a while. Really helped calm my nerves about the thing. I had posted the same question on a couple of the FB groups as well and one guy brought up a good point. I'm doing cams, right? If there's carbon in between the valves and seats, that'll really mess up my lash adjustments.

I busted out the leakdown tester again today. Turned it up to 90PSI and installed it into each cylinder and gave each valve a handful of taps with a hammer and punch. Leakdown dropped from ~50% on the bad cylinders down to ~10% on all four. Might've just saved me from messing up the valve lash when the new cams go in.

I sold the head and turbo setup of my NA, as well as the Teins off my NC this week. Took the winnings and ordered up a set of Esslinger Stage 2 cams, a Fluidampr, Brian Crower valve springs, oil pan baffle, balance shaft delete kit and some other small parts for the 2.5L motor. All I need now is a crank bolt and a couple other things and she's ready to go together.

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I friggin love it. I've seen that hammer trick done, makes sense, glad theleakdown is looking good again. It surely improves a bit more once the motor has run and heat cycled (and the test done while warm). Actually really stoked for this round of mods. Are you going to dyno it now first? I'd love to see the difference!

Deleting the balance shafts is part of what makes the K-swap in Miatas so horrible IMO. I've heard similar issues with Ecotecs with deleted balance shafts, once you get to bigger 4 cylinders (2.0+) they're not a terrible thing to have in a inherently unbalanced engine (all hail the I6)

If it's required for the swap, I get it, but if you can keep it, I'd suggest you do.

Dude it was actually pretty sick. Each leaking valve sealed up basically on the first whack. I'm sure it'll get even better once the motor's run but I'm happy with it for now.
I'm trying to get the car dyno'd this Saturday so I can class it for NASA TT races next weekend. Can't find anyone available with a Dynojet this Saturday so worst case scenario I'll just use NASA's dyno next weekend at the track. With the catless header, 2.5" exhaust and tune, I'm expecting ~145whp. Based on what research I've done, the car MIGHT hit 150whp. Stock NC1s seem to usually sit around 125-130whp but the car feels a good bit quicker than when I got it. 2.5 with the cams I got should be good for around 175whp but with a much fatter torque curve and more power approaching redline.

So the balance shafts have to be deleted as part of the swap because the original 2.0L pan needs to be used and said pan won't clear the shafts. Are the issues you're referring to NVH-related? Or longevity-related as well? I do get that they exist for a reason. That being said, the 2.5L is just about the same weight as the 2.0 with the shafts deleted, so I'll take that as a consolation prize.

The one 2.5 swap I've driven didn't seem to have insane NVH, but I have seen complaints about NVH in this swap.

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I second this motion as the "balance shaft deleted K24" guy... Comfort is one thing, but I can't begin to tell you the number of additional nut/bolt checks I've added to my list now because everything in the engine bay is more susceptible to shaking loose. 2nd order vibrations can get serious, and while laying out boosted K-series options, I've had strong considerations of moving to a K20 to virtually eliminate 2nd order vibrations. As an added benefit, the K20 can manage a bit more boost because of thicker cylinder walls....

I feel like the K20 clears up two major issues I have with the KMiata swap, assuming you raise the engine mounts and crankshaft centerline to keep the cylinder head in the same place. More oil pan and exhaust clearance, less vibrations from the shorter stroke. My dumb daydream is to use a K24 block with a K20 crank and longer rods. A better rod ratio will help it be even happier revving to ridiculous speeds. I'm not sure why Kpower started steering people away from using a K20 soon after they starting shipping these kits, and I'm too lazy to deep dive the differences in mounting them.

Anyways, sad to hear you have to remove balance shafts for the NC 2.5 swap. I feel like keeping soft engine mounts and using an engine damper like it's could 2002 and you're going to Hot Import Nights could help limit NVH while preventing the worst of the engine movement, but I've no idea how well those work.

Thanks for the input, Pad. I hadn't considered those potential ramifications specifically. Guess I'll be adding (more) routine bolt checks to my checklist on this car. Maybe grab an extra tube of loctite for the race toolkit too.

Yeah, it's kind of a bummer but at the same time, I don't remember the 2.5 swap I drove being outrageously more vibrate-y than my 2.0. I drove the cars back to back and both have poly motor mounts. Maybe I was just so excited to be driving a ripper of a car that I blocked the additional NVH out of my head haha.

MOAR UPDATES!

Finally received the ECUtek tune file for my car on Monday night. Got it loaded into the car before work Tuesday morning and ripped around with it Tuesday and yesterday. Car's definitely a touch quicker with the tune equipped. It's now targeting ~13.0:1 AFRs at WOT instead of 11.5-11.8. It's got the "RaceROM" feature package equipped, which includes flat shift and auto rev-match for downshifts. Pretty fun to play around with. I took a couple datalogs last night to send back to Fab9 for revisions. Only thing I noted that's off is that at WOT around 6,300rpm, pulse width drops and AFRs lean out into the high-13s until redline. The knock sensor isn't picking anything up when that happens but I made the tuner aware of it nonetheless. I'd rather not melt a piston at the track this weekend if I can't avoid it. Also asked if they could send me a second map with auto-blip disabled. It's super cool but I don't want to have to relearn any techniques while trying to drive faster than my buddies this weekend. Normally you can switch through maps with the cruise control button, but my stock steering wheel is long gone.

I attached a log at the bottom of this post. ECUtek logs are kinda interesting. They save as excel files and are converted into tables/graphs when you open them in the ECUtek software. The cool part is that you can view them as regular excel tables outside of the software.

Also got the suspension setup dialed in a little more earlier this week. My rookie ass has never set up a set of fixed-length coilovers before, and I originally tried getting left and right ride heights perfect with each other, resulting in uneven spring perches on all corners and a horribly corner-balanced car. I aligned it Monday and drove out to find that the steering wheel wanted to pull right pretty hard because the corner weights were so far off. I shot off a few texts to one of my buddies who works at a speed shop and got some proper schooling on the subject. I got the car off the ground on Tuesday, disconnected the sway bar end links, and set the left and right spring perches at the same height down to the millimeter. Got the car on the alignment rack, set the rake (6mm), jounced it, aligned it, then neutralized the end links and bolted them back up. Car feels way better now. Still needs to be corner balanced but it'll do for the next two weekends at the track. I dropped front camber from 3.4* to 3.2* because I wasn't using all of the outer tread at the track last time running 26psi cold, and I don't want to push it running lower pressures with the current amount of tire stretch. I still need to get a tire pyrometer and really dial in my setup, but I think the car should be at a useable starting point for now. Can't wait to finally feel some of that fabled Xida magic this weekend.

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Ha, I made that same mistake in circa 2008 or so installing my first coilover setup. Adjusting all 4 collars to different heights and measuring the car (with my weight in the drivers seat) to try and get it perfect. The car was twitchy as hell and drove like trash. Then I ended up reading from Emilio to never try and "cornerweight" a car without scales, set them evenly left to right, and only adjust the f/r heights to get the rough rake you are looking for. I'd still like to cornerweight and setup my car properly but it's great right now, no complaints.

Looking forward to the next track review of this thing, it's gonna be transformed!

Also, doesn't 13's AFR under WOT seem a bit lean? I know I know, N/A/ stuff, but I would think you'd want to target like 12.7 or something at WOT.

Dude, glad to hear I'm not alone! Felt so dumb making that mistake after having played with the suspension on my previous track toy for over two years hahaha. I'm excited to see the improvements too!

So the engine's running at an AFR of 13.0 during WOT until 6,300rpm which seems maybe a touch lean but not TOO lean to me? I'm not a professional though, so I can't comment on any other parameters/dynamics about this engine that might affect acceptable AFRs.

I emailed Fab9 about the pulse width drop and leaning out towards redline and just received a revised tune. Gonna load it up tonight and will report back. Maybe take a video of flat shifting the car too. The exhaust note sounds cool as hell during flat shifts haha.

Also confirmed that the "RaceROM" features can only be turned on and off via the cruise control buttons. My factory steering wheel is long gone (sold it on FB marketplace) so I'm SOL there. Fab9's going to send a duplicate tune with auto-blip disabled so I can still feel cool heel-toeing at the track this weekend.