When an engine fails an owner can scrap it, replace it with the same motor, or do an upgrade. That last option typically comes with some big hurdles, though for NC Mazda Miata owners, one upgrade is actually far easier than you might think.
A good engine swap usually includes at least one of the following: more performance, ease of installation, reasonable pricing, or added long-term flexibility. The one that we’re talking about today includes all of those. In fact, it might not just be reasonable pricing but outstanding pricing, and it’s a bit of a performance steal.
The NC generation of the Miata came out in 2005 (as a 2006 model) and lived until 2015. Prior to that same time, Mazda and Ford had worked very closely to co-develop several engines, one of them being the 2.5-liter MZR, which you can find as a “Duratec” in the Ford Fusion, Escape (or its sibling, the Mercury Milan), or Transit Connect. (The Mazda MZR variant was used in the Mazda3 and Mazda6). That engine, many have found, is the perfect upgrade should an NC Miata go kablewy.
The Miata came with a 2.0-liter four-cylinder in the “MZR” family that made 170 horsepower and 140 lb-ft of torque. That’s enough for the MX-5 to feel fun and playful, but there’s a potential issue, too: The rod bearings aren’t keyed. In other words, those bearings don’t have a notch that prevents them from spinning, and lots of owners report rod knock that kills their engines.
“The bearing shells were stacked on top of each other, both halves of the bearing on one side. The crank was beat to hell and probably can’t be ground. On the good rods, I noticed that there was no key on the bearings to prevent spinning.”
The top comment in the thread above put it this way: “Yep, the classic NC knock of death. I see a 2.5 swap in your future.”
This brings us back to the solution phase of the problem. Ford’s 2.5-liter four-cylinder, again, co-developed with Mazda and just a rebadged version of the Mazda-built 2.5-liter “MZR,” bolts in where the 2.0-liter once did. I don’t mean that it’s kind of similar and requires minimal cutting and hacking either. I mean it literally bolts up to the gearbox and fits in the engine bay with zero hacking.
One person who did exactly this swap and posted on Reddit about it described it this way.
“This motor is close to identical to the 2.0 that came in the car. The 2.5 is just about half an inch taller overall. Otherwise, the swap consists of essentially moving all your accessories from 2.0->2.5, and adding friction washers to the cams and crank pulley.”
It’s worth noting that the 2.5-liter from the Ford Fusion was designed to work in a front-wheel drive application. To that end, those who do this swap do have to swap a few parts from one car to the other.
That includes using the oil pan from the Miata engine on the Ford engine (to fit, this requires moving the 2.5’s balance shaft assembly, which would in theory lead to increased vibrations) and swapping over the motor mounts to 2.5-liter ones that’ll let the engine sit a little lower. Seriously, this is such a popular upgrade for Miata users that there are countless threads, explainers, and DIY posts on it.
Did I mention that it’s budget-friendly too? Miata engines from this generation regularly cost around $2,000 or more. Keep in mind that using one would result in the same power output and potentially the same issues with the bearings.
On the flip side, Ford Fusion engines cost under $500 and that includes shipping in some cases. I cannot say this loud enough, you’re essentially saving significant cash while adding power, and what’s more, these 2.5-liter MZRs are borderline unkillable.
Brett Becker, who did a thorough writeup on how he conducted this swap, says the Ford engines are the way to go if you’re on a budget:
Bear in mind, engines that come out of Mazdas are generally more expensive than those that come out of Fords. I’m told it’s because of higher-quality internal parts, but it just as easily could be due to greater numbers of Fords in salvage yards.
How much of an upgrade is this really you ask? That extra half a liter of displacement only provides a small bump in overall horsepower. The Ford engine makes just 175 horsepower at its peak but it also develops 170 lb-ft of torque. Five more ponies and 40 lb-ft more torque. That’s nothing to sneeze at.
One owner in the last video embedded below estimates that it makes 40 or 50 more horsepower lower in the rev range too (i.e. it has significantly more low-end torque). That’s significant, and the additional torque only adds to the car’s fun-factor. Here’s a dyno pull with a stock Miata.
Owners with the 2.5-liter report achieving over 200 horsepower with very few mods.
Oh and don’t forget that it’s tunable. (Apparently you can just use the Miata’s stock 2.0-liter ECU, though most will tune that to match the 2.5).
Don’t get me wrong, it’s not like there’s a ton of hidden horsepower in this Ford engine. Tuning enables the owner to add things like no-lift shifting, launch control, and more.
I’ve never really wanted to own a Miata, I can’t really fit in them super well, but now… I might be shopping for one with a serious rod knock. If you want one that’s already finished, this one is on sale for $10,000.
So, horsepower made in the lower rev range is actually torque? Does it turn back into horsepower at 4000rpm or something? Lol
Honestly though, this is really cool, and it reminds me of my old BP swapped Festiva. It’s a really great thing that So many Mazdas and Fords can swap engines with each other, leading to very cheap performance. I love that this one is totally stealth as well.
Yes, if you specify the revs at which the torque is made, it’s the same thing as saying horsepower.
If a vehicle has more low-end torque, it has more low-end horsepower.
A good point. Ultimately, horsepower made at any rpm is torque (with the factor of time added).
And while I do understand the relationship between the two, (probably not as well as you do) I do find it funny when even the most seasoned gearheads refer to low rpm power as torque, and high rpm power as horsepower.
Apologies to Rivers if my comment sounded a bit snarky, I meant it to be light hearted
It comes from the fact that you can make an engine with a lot of revs (peaky engine) or a lot of torque (torquey engine) depending on its design to achieve the same max horse power number.
This reminds me, the best swap for the Miata I’ve ever seen is the Rocketeer V6 conversion. It uses a Jaguar AJ30 (or Ford Duratec 30 after 2006, I think they’re the same) 3.0L v6 and a custom harness, ECU, subframe, etc, to make a turn-key conversion. Alex formerly of Car Throttle did this one a few years ago, and I think the kit was around £8k if you already had an engine.
FIATA
That is a great way to save an old drop top!
The NC always got hate, it was the only one that was a shared platform, it too heavy with the auto roof, the smile, its not as trackable as previous models etc. I think the NB Mazda speed was peak Miata, but NCs drive just fine.
Stick Shift+ Convertible= Awesome, full stop.
Love my NC! PRHT makes a great daily driver! And the smile brings me great joy seeing it from walking across the parking lot. Like a dog… smiling and ready to go; a great companion.
This is a popular swap for 1st gen Mazda 3s, since their earlier 2.3 often died young after burning oil without warning. The ford engines were so much cheaper and easier to find when I did mine with a friend 8-9 years ago, and it’s been damn reliable ever since. Never even bothered with a tune, since I read it didn’t add much. Only issue is it struggles to idle if I’ve had the battery disconnected, but it learns where to idle after a couple of starts. Awesome that it works in Miatas too.
A friend of mine just performed this swap on his manual trans Mazda 5 too.
I still find it amusing Mazda figured out how to fuse their fun into the 5.
The Ford Fusion is a forgettable car. So forgettable, in fact, that I momentarily forgot it exists. That, combined with a recent binge-reading of sci-fi novels on vacation, left me momentarily thinking either this was another joke post or I had missed some significant technology advancements by Ford’s engine department.
I just bought a 2006 NC last month. Hoping to get many years out of the engine, as it only has 72,000 miles on it. I can’t say enough good things about the NC. It feels modern even though it’s 18 years old and I can dependably drive it anywhere (except mine won’t be seeing snow). It’s so much fun. Having an easy to operate top and AC have extended my driving season considerably. These are great cars for the price with minimal known problems. Even the engine failures are really rare. Perhaps you’ll see a name change to 2WiperNC soon.
You could glue a third fake wiper on for nostalgia.
I vote we get him a hardtop and a wiper for the rear window. Then it’s PartTime3WiperB.
I just got your username. After how long???
Mine or 3WiperB’s?
Sorry, 3WiperB’s. What is yours a reference to???
This is just my name, that’s why I was confused haha. My old spartanjohn113 username was basically a gamertag from way back. I just thought I was being edgy as a middle schooler, making 13 my “favorite number” for things. And because everyone is a fan of Master Chief, SpartanJohn117 was already taken.
The rod bearing issue is mostly a NC1 ’06-08 issue. And usually caused by people running them low on oil or poor oil quality. NC2+ engines have upgraded internals to address this (along with higher rev limit). And yes, the OEM are expensive from the junk yards because they were only put in the Miata. A late model nc2+ engine from a place like LKQ, with a warranty, is going to run that much because they are relatively rare. Some of us in certain states don’t really have the choice to swap a 2.5. There are also some downsides to that swap but I won’t get into that here.
You also need a tune and really should change out the camshafts when you’re doing the swap. They are out of an automatic Fusion after all. So it’s not all cheap and easy to do it right
Will it CARB though?
No
If it literally uses the same Mazda computer and looks stock underneath the hood I don’t know why it wouldn’t as long as you don’t advertise it.
Sort of. It uses the same computer but won’t run worth crap without a tune. Part of the swap is getting a tune. In many States including mine, they will look at the checksum in the computer to see if there’s a tune present. If there is you fail. And they run them on a Dyno here, so if it’s running like crap because you deleted the tune you’re still not going to pass
I’d check with someone who got such a swap through CARB first.
https://nasaspeed.news/tech/engine/as-complete-as-possible-how-to-do-an-mx-5-2-5-swap/
just found this.
Good find!
I will add to this (if its not in there already and I missed it) to replace the Ford oil filter housing with the Mazda one. The Ford one will leak sooner or later. Its a trivial thing to do with the engine out so might as well do it.
And if a naturally aspirated Ford 4 is a good swap, the Ecobeast 4 would be great!
The high pressure fuel pump on the back of the head causes some interference issues but I’ve seen determined swappers just hack cowl away.
I’m bolting the Mazda 2.5L from my 2012 Mazda 5 to an NC Miata trans and putting it in my Opel GT. I have the engine and it runs great (car was wrecked by a d-bag on a phone) so why not put it to good use in a little sports car?
Stay tuned if this all actually works out like my napkin sketch says it will.
That sounds like quite a project. Will the rear end take the power?
Probably not, but I planned to upgrade anyway.
It’ll work, according to TexMex motors on Netflix!
Not mentioned in the article: You must delete the balance shafts from the 2.5L and install the Miata oil pan in order to run the 2.5L in the NC Miata. I have to admit that I have not performed this swap; however, the balance shafts exist in order to mitigate a second-order engine vibration. That is, a vertical shake of two pulses per crankshaft rotation. In the Mopar world, people often delete the balance shafts when they swap in a 2.4L from a Cirrus/Stratus/Minivan in place of the 2.0L DOHC in a neon. The resulting vibration at low rpm is VERY noticeable. Since the MZR 2.5L has a 100mm stroke and the Chrysler 2.4L has a 101mm stroke, I would expect that a balance-shaft-deleted 2.5L Miata would have some obnoxious vibration at low rpm.
From the article:
I would assume that anyone performing the above steps would also know about the balance shafts, but I guess you never can tell.
A good point. Added that in!
I deleted the balance shafts from my 2.5L turbo Dodge Shadow over 20 years ago and it was my daily driver for many years after. I also added stiffer polyurethane engine mounts at the same time and vibration at idle is certainly there, it smooths out and is fine at anything off idle.
I used to have to just feather the throttle a few hundred rpms to get the CD player to read a disc and the rearview mirror is blurry at idle.
In hindsight I regret deleting the A/C much more that the balance shafts.
As a Buell (and former VX800) owner, I’m very familiar with blurry mirrors.
Balancer deletion is becoming more common on Ecoboost Mustangs and it doesn’t seem to bother anyone. There is a theory that the balancer, being crank driven, contributes to the blocks windowing at the 3rd cylinder.
I’m doing a 2.3EB swap into a 66 Bronco and deleted the balancer to gain axle clearance.
Windowing??? This is a new term to me. Gonna look this up now.
Meaning throwing a rod through the side of the block, installing a window in the block.
stuff like this is my favorite.
The NC was easily the prettiest Miata. I’m glad to see there is a reasonable way to keep more of them on the road.
No Miatas were particularly fetching but the NC looks like it was designed by GM.
I own an a pre-facelift NC2 (the one without the mustache). I think the Mazdaspeed NB is the best looking, but I like mine, too. Went NC generation for the PRHT. I thought it would be quieter, but I think the sound just bounces off all the hard surfaces like a drum and amplifies.
What a bizarre and brave thing to say
Also the basis for the Mountune 2.5L that BAC uses in the Mono!
I have dealt with many spun rod bearings. That tang on the bearing shell means nothing when clearances grow too large and the shock during directional change pushes all the oil out between the bearing and crank throw. This pounding distorts the bearing shells and the crush that held them in place is gone. In this case, if there was a tang on the bearing shells, it folds when the bearings seize to the crank. Keep going and fenestration is the next step.
You are 100% correct. The bearing tang or tab is intended ONLY to align the bearing in the bore. It CANNOT prevent the bearing from spinning under load. Bearing crush (the radial force imparted when the two halves of the bearing are tightened together) is the design feature that prevents a spun bearing. How do I know this? I have been ASE master certified for over 25 years, and I have worked as a technical training instructor for some well-known auto makers for over 25 years. Also, see this: Design-of-crush-height-for-reliable-press-fit-of-high-performance-bearings.pdf (kingbearings.com)
Well that’s not totally accurate, is it? When you install the bearing cap, the bearing cap hangs over the tang groove of the top bearing, and that will help keep it from spinning.
It’s not much area, and if there’s no crush anymore I’m not sure how much it would help, but I certainly wouldn’t use all caps to say the tang CANNOT help prevent bearing spinning.
If the bearing tang/tab played a meaningful role in preventing a bearing from spinning, then why did Mazda (and other automakers too) design a connecting rod & bearing without such a tab? If the bearing wants to spin (usually due to lubrication failure and/or excessive clearance to the shaft), it will spin and will murder the tabs in the process.
Excellent use of the word “fenestration”
The accidental window to your engines soul. In some cases, the internal fire is released, never to be recaptured…
This is definitely the move on the NC.
Oh this is marvellous!
Thanks for the reminder to get back to looking at high mileage NCs on Facebook and Craigslist!
These MZR engines were so good that Ford still uses a variant of the same 2.5 mentioned here in the present-day Maverick hybrid.
You can then send in a junkyard 2.5 to these fine folks and turbo it to hell and back for over 700 hp…
A 700 hp Miata would very much be my type of car…
Famous last words, usually preceding “hey guys, watch this!” or “hold my beer”
Not an LS swap don’t want /s
This sounds a whole lot easier.
There are 2.5L swaps into RX-8’s as well, since they have a very similar chassis to the NC, and the front subframes swap.
I was pretty surprised at how cheap the MZR 2.5 is from auto recyclers when I was looking into it as worst-case scenario for oil consumption issues in my Mazda5 – definitely less than $500
Awww why would you want to swap this onto an RX-8 wouldn’t you miss having to add oil every refueling haha
There’s a pretty competitive turbo 2.5 MZR in an RX-8 that’s been run in Solo nationals recently… I think if I were to go non-rotary for mine I’d look very closely at the Keisler Automation GM LFX (high-feature V6) swap kits too, since those engines are also really cheap but are a significant power upgrade stock – however I’ve only got about 10k on the Renesis rebuild, so hopefully making that decision is a ways off
I was looking heavily into this, the Keisler swap kit alone is $9000 though. Rough.
Exactly, and that’s the problem with a lot of swaps including the aforementioned ls swaps… It’s not just the cost of the engine….
Was reading through the article and thinking, didn’t 100PercentJake do a video on this topic recently? Glad to see he got the shout out
Really a no brainer if you’re a Miata owner in the situation. To the point where, if you’ve got a higher mile NC, I sort of wonder if it makes sense to do the swap preemptively vs waiting till failure? If you plan on keeping it as a forever car, anyway
Friend of a friend did this, bought one as a race car, swapped the engine because cheap performance, and given it was tired anyways, there’s zero shame in swapping it and changing out most of the suspension. It’s worn anyways, why not make it better?