Miata Meets Uncle Rodney - A 2.5L Swap Story

Runalot

Runalot

Joined
Mar 18, 2023
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A few years ago, I picked up a 2006 Miata with around 100k miles, blissfully unaware that the 2006–2008 NC Miatas have a bit of a rod bearing appetite. Fast forward to the last drive of the 2024 convertible season, and wouldn’t you know it—Uncle Rodney showed up, knocking like he was trying to sell me extended car warranties. Yes, the oil level was fine. No, it never ran low under my watch.

Now, as luck (or corporate partnerships) would have it, this Miata’s 2.0L engine shares a strong resemblance to the Ford Duratec 2.5L found in Fusions, Escapes, Transit vans, and more. And thanks to Ford churning these things out like a fast-food chain slinging burgers, they are dirt cheap and plentiful. Enter my solution: a $320 special from LKQ, complete with a picture of an allegedly good compression test. What more could I ask for?

For context, my car guy journey started with binge-watching Top Gear, then falling down the rabbit hole of YouTubers like Vice Grip Garage. Eventually, I thought, “Why should they have all the fun?” I went from just changing my oil to progressively more questionable automotive shenanigans. And here I am—about to tackle my first engine swap.

Currently, the 2.5L sits on the stand, stripped down, and because I couldn’t help myself I had to pull the valve cover. Enjoy some pics of a 2.5L Duratec with 70k miles and a history that’s as unknown as the mystery meat in a school cafeteria. I’ll keep this thread updated as the swap progresses, so stay tuned for more wrenching, occasional cursing, and probably a few surprises along the way!

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If it were mine I would have first checked if a Honda K24 would fit. It's likely a better engine in all categories. And also likley also plentiful and low cost. Honda made a heck of a lot of them and they last. So there's little demand for them and likley plenty of used ones.
 
I have an ND series, so this isn't applicable to me.

But I've been aware of these swaps and they are supposed to be very exciting to drive; a lot more midrange torque and a tad more HP.

I'll be very intrigued to follow your story along as it develops.

That engine sure looks clean!
 
JimPghPA said:
If it were mine I would have first checked if a Honda K24 would fit. It's likely a better engine in all categories. And also likley also plentiful and low cost. Honda made a heck of a lot of them and they last. So there's little demand for them and likley plenty of used ones.
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A k-series would absolutely fit and would be a blast. Given my current automotive skill set a 2.5L felt like it would give me the best chance of success. We'll see!

Here is a comparison of a k-series and 2.5L swapped NC Miata:

 
fantastic said:
Looks real clean & yeah show us your progress. Does the 2.5L have more power?
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dnewton3 said:
a lot more midrange torque and a tad more HP.
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Great question!

In stock form, horsepower is roughly equal. As @dnewton3 mentioned, the 2.5L brings a bunch-o-torque in the midrange.

Here is a quick comparison.
2006 Miata 2.0L2014 Ford Fusion 2.5L
Horsepower170 HP @ 6700 rpm175 HP @ 6000 rpm
Torque140 ft-lbs @5000 rpm172 ft-lb @ 4500 rpm

Many folks change cams on the 2.5L during the swap, but given this is my first go around, I'm going to save the ~$600 and run the 2.5L stock cams....for now.... ;)
 
Runalot said:
Great question!

In stock form, horsepower is roughly equal. As @dnewton3 mentioned, the 2.5L brings a bunch-o-torque in the midrange.

Here is a quick comparison.
2006 Miata 2.0L2014 Ford Fusion 2.5L
Horsepower170 HP @ 6700 rpm175 HP @ 6000 rpm
Torque140 ft-lbs @5000 rpm172 ft-lb @ 4500 rpm

Many folks change cams on the 2.5L during the swap, but given this is my first go around, I'm going to save the ~$600 and run the 2.5L stock cams....for now.... ;)
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There's some cam/crank sensors that are different between the Mazda and Ford engines. You might have to swap in some Mazda parts.

That 32 ft/lb will be nice!
 
DBMaster said:
What is the difference in weight between the two engine assemblies?
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Great question. I generally see a 30 to 40 lbs difference listed on the interwebs. When installed, the top of the engine sits about 1/2" higher.
 
SwampSurvivor said:
There's some cam/crank sensors that are different between the Mazda and Ford engines. You might have to swap in some Mazda parts.

That 32 ft/lb will be nice!
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You're absolutely correct! Cam sensor will be rehomed from the 2.0 to the 2.5L (along with many other bits).
 
Recently bought a 2008 Miata with the 2.0. Only 8K miles on it. Hoping the rods stay where they belong for a good long time.
Watching this thread with interest. Should be interesting. Thanks for sharing the adventure.
 
Ronsant said:
Recently bought a 2008 Miata with the 2.0. Only 8K miles on it. Hoping the rods stay where they belong for a good long time.
Watching this thread with interest. Should be interesting. Thanks for sharing the adventure.
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@Ronsant - Welcome to the thread!

My 2.0 failed with ~123k miles. Your 2.0 with 8k miles will likely serve you well for many, many years. Drive and enjoy it!
 
Runalot said:
@Ronsant - Welcome to the thread!

My 2.0 failed with ~123k miles. Your 2.0 with 8k miles will likely serve you well for many, many years. Drive and enjoy it!
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I’ve read how Miata’s are great drivers cars, and I have to say it’s not the fastest car I’ve owned, but it is the most fun.
 
My 97 sure was fun. Truly a unique vehicle. That 2.5 will bring a grin no doubt. It won’t even have to work to do it, pushing the little rollerskate around!

Love the K24, but yeah this should be a little easier of a swap.

Your “new” 2.5 looks clean. Have you had to resist the urge to “start it” on the stand?
 
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