We’ll spare you the long introduction and start with a simple truism: Car enthusiasts always want more power. The problem? The days of seeing a 20% horsepower increase from a simple intake and exhaust change seem to be behind us, as modern cars come better and better optimized from the factory thanks to ever-increasing fuel economy and consumer demands.
These days, adding a cat-back exhaust is just as likely to give you a headache as it is to free up horsepower. Face it, unless your car came from the factory sporting a turbo, it’s tough to quickly and cheaply make big power gains. Fortunately, there’s another avenue: engine swaps.
It’s about a different phenomenon, one brought about by a limitless well of online knowledge and Lego-like parts interchangeability. We’re talking about barely detectable bolt-in swaps that increase displacement without requiring special wiring, custom mounts, or a healthy payoff at your local safety inspection station. Case in point: Good-Win Racing’s 2.5-liter-swapped NC-chassis Miatas.
What’s the big deal? Here’s the elevator pitch: Find the engine in any salvage yard, bolt it in over the course of a weekend, then pick up 30 horsepower and a ton of mid-range torque without adding any noticeable weight or losing any factory drivability or creature comforts. In short, it’s a 20% horsepower increase for less than the cost of a new set of tires.
It sounded too good to be true, so we booked a flight to San Diego so we could see it with our own eyes. Our plan: We were going to engine-swap an NC Miata in less than 24 hours.
Learning About Lego
We boarded the plane, flipped open our laptop, and started Googling. Our question was simple: What’s wrong with the 170-horsepower, 2.0-liter that comes in an NC-chassis Miata? (It’s known to engine nerds as the Mazda MZR LF-VE.) After all, NC Miatas are plenty quick enough in stock form.
Here’s the answer: There’s nothing wrong with how they drive, but they have a tendency to bake and blow up. The most common culprit is the factory plastic coolant expansion tank; it cracks and allows all the coolant to leak out, causing catastrophic overheating.
We’d already found the first ingredient for this swap–NC Miatas with blown engines–so we started looking for the other end of the equation: the engine. See, Mazda and Ford were best buddies when the MZR was developed, and the same basic engine has been sold in 2.5-liter form by Ford and Mazda since 2009. (This one is known to nerds as the L5-VE.)
Where can you find this engine? Common applications include the Mazda6, Mazda3 and Mazda Tribute, as well as the Ford Escape, Ford Fusion, Ford Transit Connect and Mercury Milan. In short, they’re everywhere, and we found them listed in salvage yards for as little as $350. Don’t want to put a used engine in your blown-up Miata? Mazda will sell you a brand-new one with a 12,000-mile warranty for less than $3000.
With these two facts in mind–failure-prone stock engines and plentiful, larger replacements–it’s pretty obvious why the 2.5-liter swap is so popular. It’s actually less expensive than replacing the factory engine, and all the same bolt-on power adders work on either engine, meaning it’s not hard at all to have a budget-built NC Miata with nearly 200 horsepower at the wheels.
The 2.5-liter engine features balance shafts sitting in a big, cast iron housing found inside the oil pan. The balance shafts don’t fit inside the Miata oil pan, so they have to go.
After removing the balance shafts, their oil passage needs to be drilled, tapped and plugged. Skip this step, and your reward will be a big internal oil leak–not good. What’s the penalty for removing the balance shafts? Not much, just a slightly rougher driving experience. We didn’t find it to be too bad.
Pre-Project Preparations
We closed the computer, grabbed our safety glasses, and hopped in a rental car. (We asked Hertz for something powered by an L5-VE so we’d have spare parts around, but the people at the counter just gave us a funny look and a Buick.)
Good-Win Racing is located 20 minutes from the San Diego airport, and the shop is used to out-of-towners. A fair bit of its business comes from cars that are shipped in from out of state. Though its bread and butter comes from installing parts from its vast catalog, it does 2.5-liter swaps in-house as well. The price? A little more than $1500 in labor, plus the cost of the engine.
We should mention that Good-Win also offers a fix for that failure-prone plastic coolant expansion tank: a Moroso aluminum expansion tank custom-built for the application. At $219, it’s easy insurance for any NC Miata.
Time to get started. First, though, let’s go over the ground rules. We’d be starting with a running, driving NC Miata. Good-Winpicked it up for $5000 before our arrival. We took it for a spin around the block and confirmed that it was, indeed, a running, driving Miata, then parked it on the lift and turned to the other piece of the puzzle: the engine.
Good-Win normally uses brand-new crate engines since, in owner Brian Good-win’s words, “They’re an amazing deal.” But for this budget-oriented project, the shop sourced the 2.5 from a local yard for $458.
Also present was a refreshingly small pile of parts to complete the swap, as well as Rocky from Rocky’s Miatomotive, Good-WinRacing’s in-house installation facility. He’d be taking the lead for the swap.
Work started at about 5 p.m., and 3 hours later the stock engine was out of the car. Before installing the 2.5-liter, we had to delete the balance shafts. They don’t fit with the Miata oil pan and also add extra rotating weight.
The balance shafts are fed by an oil passage next to one of the crank journals, so simply removing the shafts causes a massive internal oil leak. To maintain proper oil control, we drilled and tapped the hole so we could epoxy in a plug. Easy. We deemed the first night a success and went out in search of beer and tacos while the epoxy dried overnight.
Good-Win Racing prefers swapping engines from above, not below, yet the transmission and powerplant frame still need to come out. The stock pieces are all retained for the swap and, yeah, you might want to use a lift for this project.
Time to Transfer Parts
We were back at it the next morning. First up was the oil pan, which was transferred with its matching oil pickup to the new engine. The 2.0-liter’s oil filter adapter was swapped over, too.
Then the engine was flipped back over, and the hard part began: transferring the 2.0-liter’s lower intake manifold so the formerly transverse-mounted engine could fit in its new north-south home. What’s so difficult about that? The 2.5 has bigger intake ports, so the bolt holes don’t line up. Fortunately, even this isn’t that big of a hurdle. Rocky showed us how he removes the manifold’s locating pins and then opens up the bolt holes with an angle grinder and drill.
Once he’d created enough room for the hardware, the ports themselves easily lined up. (The ports are nearly the same size and match up fairly well.) After modifying the gasket accordingly, he bolted on the intake. Done.
We then swapped over the 2.0-liter crank pulley, coolant plumbing, EGR system and valve cover. The larger engine was now ready to install. By 10:30 a.m., we were hooking up the engine hoist.
Oh, we do have one caveat here. Before installing the engine, Good-Win swapped in a set of Stage 1.5 Xero Limit re-ground factory camshafts. This is an easy upgrade while the engine is already out and apart; once the engine is together, difficulty goes up. Could we have kept the 2.5’s stock cams? Absolutely. Brian says they’re just a bit too truck-like for his tastes.
The hardest part of this swap is adapting the 2.0-liter’s lower intake manifold to the 2.5-liter engine block. The ports and studs are close but not an exact match. Fortunately, it can be fixed with careful grinding and notching. Even with the mismatched ports, however, the 2.5 still delivers a performance upgrade.
Swapping for Science
The two engines are so similar–the 2.5 is about an inch taller, but no more–that installation was a breeze. We used stiffer Good-WinRacing engine mounts to firm up things a bit, but any 2.0-liter mounts would work just fine.
We spent the next few hours reattaching accessories, all of which come directly from the 2.0-liter. Even the a/c is retained, and you don’t need to crack open the system for the swap.
Along the way, Rocky showed us how some minor clearancing is needed here and there– such as grinding off one clip from the stock 2.0 intake manifold and bending the EGR tube a little bit–but overall it went back together just like it came out. The 2.0-liter fuel rail, injectors, and wiring harness are all retained.
The stock clutch and flywheel are usually up to the additional power of the 2.5, but in another case of “while we’re in there,” we grabbed a used ACT pressure plate and a fresh clutch disc off the shelf and bolted them onto the stock 2.0-liter flywheel. Brian says lightweight flywheels are a popular upgrade, but for a street-driven car he prefers the vibration damping (and cost savings) of the heavier stock unit.
A 2.5-liter swapped NC Miata can use almost any accessory designed for a normal Miata, so we grabbed a beautiful RoadsterSport exhaust system off the shelf and used it instead of the factory pieces (though they, too, can be retained for this swap). The stock radiator can stay, too, but we replaced it with a Good-Win Racing Triple-Pass 32mm Race Radiator since this car is destined for track duty in Southern California’s heat.
After bolting everything together, we plugged in a laptop and flashed the car with a Xero Limit tune specifically for this swap. Time! We turned the key and heard the salvage yard 2.5-liter roar to life. We’d done it. Less than 24 hours after landing in Chula Vista, we were about to take our freshly swapped Miata for a spin. Of course, that meant loading it on a trailer–see our sidebar on CARB approval.
If you live in a state with emissions inspections, we already know what you’re thinking: “Wait a second, is this swap streetlegal?”Good-Win Racing is quick to point out that the 2.5-liter swap is not CARB-approved, so we were only able to drive this California-registered car on closed courses during our visit. Would this swap pass a visual test? That is between your conscience and the inspector.
The instruction manual for this swap is quite simple: If something looks different on the 2.5-liter, just swap the 2.0-liter part onto it. Everything basically bolts right on, including the 2.0-liter's PCV assembly.
After transferring over a few more things–and installing a pair of re-ground camshafts, we were ready to bolt in the 2.5-liter engine.
Driving Our Budget Beast
So, how did our freshly swapped Miata drive? Like a faster Miata–but let us clarify. We’ve driven fast Miatas before. We’ve driven them with bolt-ons, with turbos, with superchargers, with V6 swaps, all the way up to insane V8-swapped cars that grab all the headlines in the fast Miata world.
On that spectrum, we’d describe this car as “Bolt-Ons Plus.” It didn’t lose any of that Miata feel or soul or whatever you want to call it. It was just faster–and torquier. No turbo lag, no V8 rumble. It hadn’t been turned into a different sort of car, just a faster version of the same thing. In short, this feels like the engine Mazda should have installed from the factory. Not exciting enough for you? Don’t forget that almost anything designed for a 2.0-liter will fit on this engine.
Mission over, case closed, end of story. We flew home and jotted down a note on our to-do list: Buy the next cheap blown-up NC Miata we find.
To an untrained eye, the 2.5-liter’s engine bay is indistinguishable from the 2.0-liter installed by the factory. The bigger engine, obviously, offers more torque and horsepower.
But How Fast Is It Really?
We were left with a lingering thought: Was that thing actually fast, or just faster than it was? The dyno report showed that we had in fact made gains. The car now made 196 horsepower at the wheels, picking up about 40 horsepower and 50 lb.-ft. (In both cases, the engine was breathing through a cat-back exhaust.)
Next, how was it around the cones? For this step, Brian fitted 10-inch-wide wheels wrapped with sticky tires. Here’s what he sent after running a local autocross with the car: “There were about 100 competitors–and our NC Miata with a $458 junkyard motor was the fastest thing with doors! It was the fastest thing with a/c, the fastest thing with a stereo, a roof, air bags, etc.
“We had Top Time of Day until the very last run, when a formula car on fresh Hoosier slicks beat us by a few tenths of a second. We were running Rival street tires and could have probably picked up about 1.5 seconds faster on that long course if past experience at that site is any indication.
“Not bad at all for a budget project that got built super-fast and had almost no time for testing/tuning/setup improvements! We beat all the Corvettes, the Porsches, the turbo Catfish, the Ferrari and lots of other expensive stuff. Super proud of our budget-built NC.”
Many of us dream about swapping in the meanest, craziest engine. But sometimes, a simple upgrade just does the trick.
For more photos from the swap, head on over to grassrootsmotorsports.com/25swap. (While this seems like a quick overview, really it is kind of simple.)
