Project Endurance Miata: Fitting Our LFX V6

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Update by Tom Suddard to the Mazda Miata project car
Feb 27, 2020

Our last update ended with our trusty endurance racing Miata on the lift and $10,000 in parts sitting next to it. That’s right: After years of developing our turbocharged Miata, we had new goals: Kick it up a notch, move away from $500 budget racing, and go really fast.

Long story short, it was time for a V6 swap. The promise was simple: Two more cylinders, roughly the same weight (the Miata’s turbocharged iron-block four-cylinder is traded for an all-aluminum V6) and nearly 300 horsepower. It would split the difference between our turbo four and a heavy, overpowered LS swap, and meet our goals perfectly.

You can read more about our rationale for the swap  in our previous update, but our minds were made up: We were Chevy LFX-swapping our Miata.


Out With the Old

Before we could do anything, we needed to get rid of the Miata’s drivetrain. So we did, throwing the Mazda front subframe, engine, transmission, driveshaft, powerplant frame, differential and axles in a pile for a future project. We saved the front suspension components, since they’ll bolt on to the new V8 Roadsters subframe.


Time to Cut

Our Miata was now less one drivetrain, so it was time to get to work on installing a new one. Very little in the way of instructions are included with the V8 Roadsters swap kit, but we had an ally to help with that:  V8R Performance, the brand’s turn-key car building division, is located just a few minutes from our shop.

Owner Al Ludington went above and beyond to show us how to swap our car, even joining us in the garage on more than one occasion to handle the hard parts for us. And that support extends to normal V8 Roadsters customers, too, as Al has built an extensive library of photos and how-tos for customers to reference while building their cars.

This is probably a good time to mention that the LFX is definitely not a bolt-in swap. In fact, it’s impossible to complete without a welder and a willingness to cut up the car a bit. 

Case in point: The next step involved a plasma cutter, a Sawzall with an 18-inch-long blade, and a few grinding discs. NA- and NB-chassis Miatas have oddly shaped engine bays, with both framehorn-like unibody structures widening towards the firewall to create a V-shaped engine compartment that works fine with an inline-four, but interferes with a V6 like the one we were installing. We cut these structures out, creating a square hole for the engine.

Did we remove strength? Kind of: V8 Roadsters’ kit included some nifty steel reinforcement plates that we welded in place of the original sheet metal. These are way thicker material than the stock sheet metal we removed, so we’ll call the strength question a wash. We’ve cut this area out on a few engine-swapped Miatas and never had a problem. 

There was one more area we needed to clearance: In order to make room for the LFX’s driver’s-side cylinder head, we needed to slightly massage the firewall a bit. Al walked us through this process, which basically amounted to “Remove the heater core, smack the area where its coolant connections pass through the firewall with a hammer, then reassemble and enjoy.” And to answer your question: Yes, it’s possible to keep the heater with your LFX swap. 

Because our Miata is a race car, we decided to save some weight and leave out our car’s heater core. Instead of reinstalling it after massaging our firewall, we instead covered the holes with a piece of sheet metal riveted in with seam sealer.

We put the plasma cutter away, but still needed the welder: A stock Miata uses an aluminum beam connected to the transmission, called a powerplant frame, as the front differential mount. Since we were deleting the Miata transmission and differential, we also had to get rid of our powerplant frame, meaning we needed to find a new differential mount. V8 Roadster’s kit included weld-on differential brackets, which we trimmed and welded to the rear subframe in order to mount our Cadillac CTS differential. Note that while this step didn’t technically require the rear subframe to be removed, it was only a few more bolts to pull it all the way out so we didn’t have to weld upside down just inches from the fuel tank. 


In With the New

Once we’d finished cutting, we could start reassembling. The V8 Roadsters custom front subframe bolts in just like the stock subframe, so the next step was installing it and the factory control arms. That was enough to get the car rolling again, so before we did anything else we rolled the Miata outside and used our Kärcher heated pressure washer to get rid of the dirt and grease that had accumulated over 20 years of racing. 

Once the Miata was clean, we could move onto the fun part: Installing shiny new parts!

Remember that missing powerplant frame? We’d solved the differential mount, but now we needed a way to mount the rear of our Camaro transmission. V8 Roadsters’ kit included frame rail reinforcements, which bolt over top of the Miata’s flimsy sheet metal frame rails to stiffen the chassis. They also include a provision for the bolt-on transmission crossmember that also comes in the kit. One problem: These bolt-on frame rail reinforcements didn’t bolt on, thanks to that dropped driver’s floor we installed in the car in order to fit our larger drivers. This wasn’t a big deal, but did mean we broke out the plasma cutter and the welder to finish the installation.


What About That Oil Pan?

You don’t technically need to replace the oil pan on your LFX before you swap it into a Miata, but you really should. Why? Ground clearance, or more precisely a total lack of it.

A stock Camaro pan puts the oil pan nearly two inches bellow the front subframe, making it an easy target for rocks, squirrels or curbing. The V8 Roadsters kit includes a brand-new LFX pan that’s been modified to better fit the Miata, so our next step was swapping it onto our engine. We’ve heard horror stories of leakage from earlier V8 Roadsters pans, but ours had beautiful welds and a flat flange, and hasn’t leaked a drop. 


Engine, Meet Transmission

Subframe installed, differential mount finished and frame rails reinforced, we were finally ready for the V6. Al told us the drivetrain was easiest to install as a unit, so we bolted our LFX V6 to our MV5 transmission on the bench before inserting things into the car. 

Wait! What about that heavy dual-mass flywheel that comes with an LFX!?” Relax, relax–we hear you, and we addressed it.

These engines come with 50-pound dual-mass flywheels in order to damp vibrations. We didn’t want one for two reasons: First, dual-mass flywheels introduce more failure points, which is bad in an endurance race car. And second, dual-mass flywheels are really heavy, which adds weight to the car, makes it harder to rev-match downshifts, and speeds transmission synchro wear. 

There isn’t nearly as much aftermarket support for the LFX as there is for its eight-cylinder siblings, but there is at least one company making clutches and flywheels for it: We called SPEC and ordered a stage 4 clutch and lightweight aluminum flywheel. This combination shaves 20 pounds compared to the stock parts, and is rated for up to 463 lb.-ft. of torque. Did we need that torque capacity? Absolutely not, but this was the least aggressive clutch that didn’t feature a sprung hub, which reduces vibration and softens engagement on street cars. We don’t care about comfort, but we do care about failure points, and this solid steel hub eliminates one. 


Installation Time!

Our engine and transmission were now one, so it was time to stick the combination in the car. This turned out to be… easy. Seriously, it dropped right in, settling onto the V8 Roadsters engine and transmission mounts on the first try.

Magic? Witchcraft? We’re not sure, but we stepped back to admire our newly-minted V6-swapped Miata with smiles on our faces.

Of course, there’s still a lot to do–we’ll tackle wiring, plumbing, axles, suspension and so much more in future updates. 

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View comments on the GRM forums
David S. Wallens
David S. Wallens Editorial Director
2/27/20 11:53 a.m.

And starring Jesse. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
2/27/20 12:05 p.m.

Facial expression on the first photo is worth the price of admission alone.

SVreX MegaDork
2/27/20 1:36 p.m.

This is really awesome!

David S. Wallens
David S. Wallens Editorial Director
2/27/20 7:52 p.m.
Vigo MegaDork
2/28/20 12:21 p.m.

this was the least aggressive clutch that didn’t feature a sprung hub, which reduces vibration and softens engagement on street cars. We don’t care about comfort, but we do care about failure points, and this solid steel hub eliminates one. 

Big mood as they say. I wish i could get unsprung full face organic disks. frown 

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