If you have owned an underpowered car with a weak motor, then undoubtedly you’ll be tempted by the notion of performing a motor swap. It’s usually an arduous undertaking, and the results might not always be what you expected. Therefore, only those who are really dedicated can tackle a motor swap project.
However, when done properly with all the chassis upgrades necessary performed, a motor-swapped car can be an absolute peach. And for motor swaps, one of the most common candidates is the Mazda MX-5 Miata.
It makes sense if you think about it. The Miata is the best-selling convertible sportscar across the globe, which makes them affordable and accessible. Furthermore, the longitudinal rear-wheel-drive platform also broadens the choices for performance motor swaps.
The Miata’s chassis is also well developed with an extensive aftermarket for it. This means that all the parts surrounding it are easy to find and relatively cheap. Finally, with the Miata, a common critique is that it’s lacking in power. The original Miata only had a 1.6-liter B6 to start with, and it’s not until later that the 1.8-liter BP was made available.
This means that owners have two ways to approach this. You either make performance modifications to the motor, such as forced induction; or you can ditch it and go one step further: swap it out with a bigger, more potent powerplant. For most people, the former is enough, as the Miata’s motors are surprisingly capable given that you set your expectations accordingly.
Miata for Motor Swaps
For the rest though, the latter might be a better option. Whether if it’s swapping it out with another inline-4 to preserve the balance, or going all out with a V12 motor, people have done it all. In fact, rotary motors from its distant relative have ended up in the Miata too.
However, if you’re trying to preserve a modicum of balance in the Miata (as was intended by Mazda), then the biggest you can pragmatically fit within the Miata’s motor bay is a V8. And it just so happens to be one of the most common swaps performed on the Miata.
The reasoning behind this is due to the fact that modern V8 motors can be very lightweight due to modern construction techniques with aluminium alloys. And some V8 motors are quite compact in dimensions, allowing them to fit neatly within the Miata’s modest engine compartment.
Furthermore, a V8 motor, even if naturally aspirated and unmodified, offers a good step up in terms of performance compared to the stock inline-4. For example, even an LS small-block truck motor would offer over 2 times the power and 3 times the torque at a much lower RPM.
And power doesn’t necessarily compromise the vehicle’s handling. In fact, there are V8 propelled Miatas out there built to run time attacks. People that go through all the effort of replacing the stock motor with a V8 are also those who frequently go to track days in their Miata.
However, what if you don’t want any of that? What if you’re just looking for the most ridiculous head-turner of a Miata? Maybe you just want a whole lot of tire smoke and have a great time doing it. Then there’s also the option of a Hellcat motor.
Everyone who is into cars knows what the Hellcat nameplate signifies. It’s a lineup of high-performance models Dodge produces that’s powered by the 6.2-liter supercharged HEMI V8 dubbed the Hellcat.
The Hellcat is part of the modern 3rd-generation HEMI motors. It’s only HEMI in name though, as the modern revived HEMIs have pent-roof combustion chambers rather than hemispherical ones.
Originally, Dodge only put the Hellcat motor into the Charger and Challenger models. Since then, it has made its way into a multitude of Dodges and other domestic brands under Stellantis. Such as the Jeep Grand Cherokee Trackhawk and RAM 1500 TRX.
Now, Dodge even offers the Hellcat motor as a crate motor. This means that anyone with enough money can order a brand new Hellcat motor directly from Mopar.
This got some enthusiasts thinking, what if someone transplants the Hellcat motor into the Miata? It would surely make one hell of a convertible sports car.
Despite it sounding like a wholly unrealistic project, all it takes is for one pioneer to take the leap and figure things out along the way. Thankfully, someone did, and what they have achieved is nothing short of astounding.
You might have heard of this. The Hellkitty is a well-known Miata featured in many articles and videos. It’s a Hellcat-powered second-generation NB Miata and it is as ridiculous as it sounds.
If you’re questioning whether if the Hellcat motor can even fit inside the Miata, the answer is not really. The HEMI by itself isn’t exactly massive. But when you add the massive 2.4-liter Hellcat supercharger, it is lofty.
That’s why that the project builder by the name of KARR had to cut out a massive portion from the NB Miata’s hood just to be able to close it.
So why would one undertake this whole endeavor? Well, to put it plainly, it’s for the Internet. They started off by thinking what crazy build would entice viewers, and Hellcat Miata sounded appropriate.
The entire process took 2 and a half months to complete. What they ended up with is an HPTuners tuned 6.2-liter Hellcat-powered Miata with a Tremec TR-6060 6-speed transmission.
It’s basically Hellcat power in a chassis over 2,000 lbs lighter than the Hellcat Challenger. It’s running race slicks all around, has a full set of V8Roadsters coilovers, 8.8 Cobra 3.73 rear differential, custom drive axles, and uprated brakes.
The Parts List For Hellcat Maita Engine Swap
If you’re interested to make this swap yourself, then you’d be glad to know that they’ve gone through the effort of documenting the entire process on video.
First, you need a Hellcrate Hellcat crate motor, which costs about $20,000 from Mopar. You can order the TR-6060 from them too, for an additional $5,250. This gets you 700 horsepower and 650 lb-ft of torque.
You can also obviously source your own transmission. Those who intend to extract even more power might need a built T-56 Magnum. There’s also the ZF 8HP90, the 8-speed automatic option.
If you’re insane enough and want to dial it up further, Mopar sells upgraded Redeye Hellcrate which makes over 800 horsepower and 700 lb-ft of torque.
Unless you’re prepared to do a lot of wiring work and go with a standalone motor management unit, then you’ll probably want the Engine Kit. This includes all the wiring harnesses needed to get the motor started and running.
With the stock ECU, you’re also going to need an instrument display that can read off the OBD2 CAN BUS from the ECU. A standalone management unit should be able to get just about any sort of display running though.
Other than that, the front-end accessory drive (FEAD) kit is also important as it comes with all the drive pulleys and the alternator.
It’s also possible for you to find a crashed Hellcat as a donor car. This is actually the route that KARR went with, a wrecked Hellcat with a relatively unscathed drivetrain. You can save some money by going with a used motor here.
That’s not all, you’ll also need a front subframe adapted for the swap. KARR went with a V8Roadsters front tubular subframe kit. This saves you a lot of fabricating time.
Another crucial component is a rear sump oil pan for clearance issues on the subframe and steering rack. An intriguing idea might be to go with a dry-sump system which will reduce the motor’s mounting height. KARR went with STEF’S Hellcat rear sump pan.
Then, that rear sump pan has to be reworked further to provide for enough clearance. Part of the sump needs to be cut out so the front of the sump can slant further inwards. A competent engineering or welding shop should be able to work this out.
Since the Hellcat’s supercharger is water-cooled, you’re going to need a separate heat exchanger to run the auxiliary water lines akin to the stock Hellcat low-temperature radiator. KARR went with a FrozenBoost heat exchanger.
To save on the complexity of having to figure out all the pump mounting, hydraulic hose routing, and adapting, KARR just went with a manual steering rack from Ben’s Used Miata Parts.
Hellcat Maita Engine Swap Additional Parts Needed
You’re going to find a differential that can handle the torque on your own. V8Roadsters manufacture and sell custom-fit drive axles for the Ford 8.8 differential in Miata application. KARR went with the Cobra 8.8 with 3.73 final drive in this case.
Along with that, you’ll also need the Ford 8.8 differential mount. V8Roadsters makes one, and it mounts straight to the subframe with some welding to be done.
It might not seem obvious, but if you’re going to put 7 times the power and over 6 times the torque into the Miata, you need chassis reinforcement, reworked suspension, and enlarged brakes.
V8Roadsters sell various upgrades made to handle the extra power and torque of a V8 motor from bigger brakes, to tubular control arms, to weld-on frame rails. This is the route that KARR went with.
Coilovers with higher spring rates are definitely advised since the Hellcat motor with its massive transmission is twice heavier than the Miata’s stock 1.8-liter BP motor.
You also need to figure out a way to mate the Hellcat’s transmission to the differential. The original is a two-piece driveline, which would be a headache to adapt to the Miata.
KARR went with a Sonnax 6-bolt driveshaft flange that facilitates the use of traditional one-piece U-joint driveshafts. It’s also a lot simpler to bolt in compared to the stock Ford 8.8 mounting method.
There’s also the need to relocate the shifter since the stock transmission has a shifter extender. This is because the motor is further forwards in a typical Dodge. There’s no need for the extension in a Miata.
SilverSport Transmissions is one of the few that manufactures a short-throw shifter kit for this that fits the purpose. It eliminates the rear mount shifter in the TR6060. It’s also the solution that KARR went with.
Another popular item for most Hellcat swaps is the Schwartz Performance Hellcat Supercharger Intercooler Manifold Adapters. The stock supercharger has a massive cast manifold to allow for coolant flow to and from the intercooler which protrudes the firewall.
This adapter will provide much-needed additional clearance for the firewall area. It’s also fully billet and allows for AN fittings to be used as well as custom hose routing.
You’re going to need an oil cooler, transmission cooler, and a beefy radiator for the Miata that’s capable of cooling down the Hellcat motor too.
Making the Hellcat Swap
Once you have ordered everything you’ll need, you can finally carry out the swap. Starting off, start by stripping your Miata down to the shell. Pretty much everything has to come off to work out how components are going to mount to the chassis.
Pull out the stock motor and remove the entire front and rear subframe. The PPF has to come off too. Everything that has to do with the drivetrain pretty much needs to come out for the conversion process. You can ditch the front subframe completely for the V8Roadsters tubular subframe.
You should test fit the Hellcat motor inside your Miata to see how it’s going to sit. This gives you an idea of how much of the firewall you’re going to need to cut to make enough room for the motor.
Then, you should also guide the TR6060 into the transmission tunnel. Because it’s a massive transmission compared to the Miata’s, you’ll probably need to cut out a good chunk of the tunnel.
It would also be wise to install the oil sump before you test fit the motor if you have it on a stand. This saves you the trouble of having to work underneath the motor while you’re test-fitting it.
Once you have enough space cleared for both the motor and transmission, you can bolt them together again for a test fit inside the Miata’s engine bay.
After you’ve got the motor positioned in place, install the V8Roadsters subframe and work out the measurements for the motor mount. Afterward, it’s a process of removing the subframe, fabricate the mount, remount the subframe, and test-fit the mountings.
Make sure that the motor is situated exactly how you want it. This means that it has to be straight, level, and at the correct height. Measure twice, fabricate once.
It’s also important to ensure there’s enough space for the brake booster and master cylinder as well as the clutch master cylinder. You’ll probably be cutting out a majority of the firewall and transmission tunnel, so keep the motor position with that in mind.
If you’ve bought the Miata frame rails like KARR, it’s a good time to install these. They sit over the original frame rails and provide additional chassis strengthening.
You’ll need to fabricate a custom transmission crossmember for the transmission to mount onto. KARR made use of the frame rail by mounting the crossmember to the frame rail. It’s the only choice as the stock Miata does not have a crossmember because of the PPF.
When you’ve got your motor and transmission situated, it makes sense at this point to remove the stock Miata differential and install in the new one. With the V8Roadsters Ford 8.8 kit, the rear of the mounting bolts in, while the front needs to be welded.
After mounting the differential and reinstalling the rear subframe, make the measurements for the driveshaft. You’re going to have to commission a driveshaft fabricator to make a custom driveshaft for your application. KARR ordered it from Drive Line Service, so these folks have experience with a Hellcat Miata swap.
It’s worth noting that the HEMI motors have a common failure point which is the water pump. If you have a used motor, replacing it while you have easy access is a good idea. If your budget allows, you can even convert to an electric water pump setup. The complete kit is pricey though.
After that, you’ve got the major assemblies mounted into the car. There are still things you need to work out how to mount, such as the radiator, additional coolers, and heat exchanger for the intercooler. Keep in mind that you need to replace the stock Miata throttle pedal with the Hellcat’s electronic throttle pedal.
This is where you need to figure out all the fueling and wiring for the motor. You’ll most definitely be throwing the old Miata pump away for a high-flow one. KARR just went to the OEM Hellcat pump which will definitely supply enough flow.
A noteworthy point of KARR’s Hellcat swap is the fact that they used AN fittings wherever possible. It takes more time and money to install, but it looks great and has fewer opportunities for failure when done properly.
Be sure to patch up any glaring holes you might have made to make space for the motor and transmission. Then you can finally reinstall the dashboard and begin putting back in the interior parts.
If you have all the suspension parts ready, then you’re nearly prepared to get your Miata going again. Reinstall all the suspension components as well as the drive axles and the custom driveshaft.
If you’ve reached this point, you’re ready to sort out and plug in all the wiring harnesses. If you have the Hellcat engine kit, then this should be a relatively straightforward process of plugging things in and finding places to mount the control modules.
However, if you went with a standalone ECU, then this is a bit more complicated. You’ll need to sort out a custom harness for the motor. At this point, details for fully converting the Hellcat for a standalone management system remain relatively scarce. But there are people out there who have done it.
When you’ve done all the wiring, you’re ready to start the car. Make sure you’ve got all your fluids in there already, and have every crucial component mounted and sorted out. Go through a startup checklist.
Once you’ve got it started, pay attention to the gauges, make sure all the pressure and temperature are reading fine. Congratulations, you’ve put a Hellcat engine into your Miata!
A critical part of the build though is the exhaust header. If you’re handy at welding and making exhausts, then this should be relatively straightforward for you. Otherwise, you can always get it done by someone else. It depends on what type of exhaust setup you’re going for, but KARR went for a straightforward bumper exhaust dump.
Now you just need to get the wheels mounted and prepare for the first test drive. Ensure that the brake and clutch operate fine beforehand and keep an eye on the motor operation, making sure it works properly.
Hellcat Miata Engine Swap Worth It?
If you’ve paid attention to the development of the Hellkitty, from its initial debut at the Cleetus and Cars 2019 show, to being featured by Hoonigan and Gas Monkey Garage. It was making headlines across the car scene in America. It then got sold by KARR at an auction and then got crashed leaving a car show by its following owner.
But as far as creative motor swaps that garner attention goes, the Hellkitty definitely managed its job very well. If you want a Miata that’s built primarily for shows and burnouts, then a Hellcat swap definitely makes sense, which was the case for KARR.
However, for a practical daily driver? Then probably not so much. It’s not uncontrollable; in fact KARR would comment that it’s very drivable even for long distances. However, it is definitely overpowered for the Miata chassis. It’s a roadster with 650 whp and 635 ft-lbs of torque that weighs well under 3000 lbs.
You must be attentive to drive it properly, and KARR was running Hoosier slicks on all four corners. And you can’t even fit it underneath the Miata’s hood without a massive blower cutout.
So if you just want more poke in your Miata, maybe a Hellcat swap is overkill. However, for being a smoke generator and a good time? Then you can do a lot worse than this. If you’re interested, definitely check out KARR’s Youtube channel which has the entire build documented thoroughly. They deserve praise for going through and pulling off a unique motor swap.