Whether or not rotaries are objectively great engines is debatable and you may get a lot of flak for swapping a piston engine into your RX8.
However, it has been done countless times over, and there’s a ton of aftermarket support for projects like these. So if you’re on the fence about engine-swapping your RX8 or if you need some insight, this article is for you.
In this guide, we’ve highlighted some of the most well-recieved RX8 engine swap options for you to consider.
What Engine Is in an RX8?
Before you go pulling engines and trying to put something else under the hood, it’s important that you have a thorough understanding of what’s already there.
From the factory, the Mazda RX8 comes with the 13B-MSP (multi-side port) or Renesis engine. It’s an improved version of the previous 13B-RE and 13B-REW that was primarily designed to reduce exhaust emissions and improve fuel economy.
Unlike its predecessors from the 13B family, this engine is naturally aspirated, making it slightly easier to live with, albeit with a bit less power.
In contrast to the previous iterations of the 13B, this engine features exhaust ports that aren’t peripheral.
Instead, they’re located on the side of the rotor housing, which eliminates overlap and allows for a more forgiving intake port design. The result is a a higher compression ratio and more power from the same design.
While this does increase the chances of carbon build-up in the exhaust ports, the water-jacket passage in the side housing helps to keep the port clean.
Even the rotors are sealed a bit differently, owing to redesigned side-seals and low-height apex seals, making it a bit more reliable than its predecessors.
Considerations and Swap Options
Without a doubt, the Renesis motor is the most refined version of the 13B line-up, but the fact that it’s a rotary engine alone adds to complications when it comes time to swap it for a different motor.
It doesn’t make it impossible, just that you’re just going to have to get creative with space and be comfortable cutting, welding, and otherwise improvising to make things work.
Also keep in mind that the RX8 is a modern car, so you’ll need to replace the ECU, the dash, and get a CAN bus adapter to keep everything working the way it should. It’s possible, and it’s going to be expensive.
If you have the budget and want to swap out the engine, the perks are there. That’s because the RX8 comes with 212 or 232 horsepower from the factory, depending on the transmission.
They’re not bad performance numbers, but in the low 200s, there’s plenty of room for improvement.
You’re going to run into hiccups, headaches, frustrations, and everything else you can think of while you’re trying to complete the project. It’s really what’s part of the fun.
It might not feel like it when you’re in the thick of things but adapting and overcoming is what it’s all about.
Many people go into engine swaps thinking that it’s all about getting the new motor to fit under the hood then it’s good to go from there. We’re here to tell you that getting the new engine is the easy part.
From there, you’ll have to deal with wiring, electrical issues, and getting everything hooked up and connected to your new block. It takes time, patience, and expertise to figure it all out.
We think heading out to the garage is a great way to spend a weekend, but if that doesn’t sound like you then you’ll need to bump those installation costs up even further.
Finally, engine swaps are both fun and insanely frustrating. It doesn’t matter if it’s your first engine swap or your hundredth, you’re going to run into new problems and scenarios that you need to figure out.
On that note, let’s check out some of the best swap options for your RX8.
GM LS1
Engine Code: LS1
Layout: V8
Displacement: 5.7 L (5,665 cc)
Fuel System: Sequential fuel injection
Cylinder Bore: 99 mm (3.90 in)
Piston Stroke: 92 mm (3.62 in)
Compression Ratio: 10.1:1
Power: ~350 hp @ 5,600 rpm
Torque: ~365 lb-ft @ 4,400 rpm
Firing Order: 1-8-7-2-6-5-4-3
LS swaps are done to death, but there are many good reasons for that. They’re cheap, easy to source, parts are plentiful, and they make a ton of power. They are heavy and bulky, however.
When swapping an LS1 V8 motor into a Mazda RX8, preserving its handling characteristics is among the biggest challenges.
The LS1 packs quite a punch but also shifts the car’s weight distribution, given its larger size and weight compared to the stock rotary engine.
To counter this, many builds incorporate lightweight aluminum components for the LS1 and use custom mounts designed to position the engine as low and far back as possible.
Proper suspension tuning is essential to adapt to the altered driving dynamics, ensuring your RX8 remains agile and responsive.
Of every engine mentioned in this guide, the LS1 has the most swap support. With extensive availability of custom subframes, mounting kits, and electronics tailored for the RX8 chassis, enthusiasts can find components to simplify the process.
That said, additional modifications are necessary for compatibility. These include a reinforced drivetrain to handle the LS1’s torque, upgraded cooling systems, and an exhaust system to fit the RX8’s tight undercarriage.
Integration of the LS1’s ECU with the RX8’s electrical system can also be a challenge, often requiring specialized wiring harnesses or standalone management systems. While this swap demands time, expertise, and investment, it’s well worth it.
Expect a more linear power band, reliable performance, and the unmistakable V8 growl that’ll turn heads and shock anyone expecting to hear the usual 13B-MSP.
Toyota 2JZ-GTE
Engine Code: 2JZ-GTE
Layout: Inline-6
Displacement: 3.0 L (2,998 cc)
Fuel System: Multi-point fuel injection
Cylinder Bore: 86 mm (3.39 in)
Piston Stroke: 86 mm (3.39 in)
Compression Ratio: 8.5:1 (twin-turbo)
Power: ~276 hp @ 5,600 rpm (JDM spec)
Torque: ~318 lb-ft @ 4,000 rpm
Firing Order: 1-5-3-6-2-4
Both the Toyota 1JZ and 2JZ engines are a good choice for this swap, but we prefer the 2JZ. Installing one in your RX8 can be done, but it’s not without its headaches.
The first hurdle is that the engine is big, so you’ll need custom mounts to make it fit snugly in the RX8’s relatively tight engine bay.
It helps that Mazda engineered the RX8 engine bay to accommodate the 13B lower and further back as it helps to fit the 2JZ relatively easily.
However, it’s going to look cluttered and high under-hood temps may be a problem. Plus the 2JZ is heavier than the stock 13B, which means you might have to tweak your suspension to compensate for the extra weight.
Like with most engine swaps, expect clearance issues, like steering rack and sway bar placement. This can be avoided with the help of mounting kits as they usually come with the necessary spacers and custom parts to sort this out.
When choosing a transmission, the R154 and CD009 are popular options, but you’ll need a custom driveshaft to conect it all.
Wiring can get tricky when integrating the RX8’s electronics with the 2JZ’s ECU. A standalone or custom CAN bus module can keep your gauges and ABS functional.
Engine management and fuel system mods are incredibly important and luckily, there are heaps of options out there for you to get creative with.
Nissan SR20DET
Engine Code: SR20DET
Layout: Inline-4
Displacement: 2.0 L (1,998 cc)
Fuel System: Multi-point fuel injection
Cylinder Bore: 86 mm (3.39 in)
Piston Stroke: 86 mm (3.39 in)
Compression Ratio: 8.5:1 (varies by generation)
Power: ~205-250 hp @ 6,000 rpm
Torque: ~203-217 lb-ft @ 4,000 rpm
Firing Order: 1-3-4-2
Swapping an SR20DET engine into an RX8 combines lightweight turbocharged power with the RX8’s excellent chassis dynamics, but the process comes with its share of challenges.
The SR20DET is relatively small and light, so it preserves the RX8’s near-perfect weight distribution.
However, you’ll need custom motor mounts and brackets to fit the SR20DET into the RX8’s engine bay, as the chassis wasn’t designed for a traditional inline-4 layout.
Wiring integration is another hurdle since the RX8 relies on a CAN bus system, which doesn’t natively communicate with the SR20DET’s electronics. Custom or standalone engine management solutions are key to making the electronics work seamlessly.
Beyond the engine itself, ensuring a reliable and complete setup means addressing supporting components.
The SR20DET’s power output will require upgrades to the RX8’s drivetrain, like a compatible transmission (often the SR20’s own or alternatives like the CD009), custom driveshafts, and possibly a reinforced differential.
Cooling systems must also be upgraded, with a larger radiator and intercooler for the turbocharged engine. Additionally, modifying the fuel system with bigger injectors and pumps is essential for handling the SR20DET’s higher performance needs.
Though challenging, this swap results in a unique, lightweight RX8 with improved reliability and turbocharged thrills on the street or track.
Mazda 20B
Engine Code: 20B-REW
Layout: Inline 3-rotor (rotary engine)
Displacement: 1.962 L (1,963 cc equivalent)
Fuel System: Multi-port fuel injection
Cylinder Bore: N/A (rotary design)
Piston Stroke: N/A (rotary design)
Compression Ratio: 9.0:1
Power: ~280 hp @ 6,500 rpm
Torque: ~280 lb-ft @ 3,000 rpm
Firing Order: Sequential rotary ignition
If you love the rotary engine but want something with a little more power, why not go with a bigger rotary? That’s exactly what the 20B engine is, except it’s a 2L engine and pushes 276 horsepower.
The issue with a 20B engine swap in the United States is that this engine is illegal here. There are workarounds, but there’s a good chance your 20B-swapped RX8 won’t be street legal.
Since it never went through EPA testing (no car with a 20B hit the market in the US), it’s currently illegal to drive them on the road.
Contrary to the dual-rotor 13B-MSP engine, the 20B is a 3-rotor engine, which lets you get far more power out of it.
Unlike the LS engine swap kits, if you’re looking to install a 20B into your RX8, you’ll need fabricate some parts. That’s because they 20B swap kits for this car aren’t easy to find in the US.
If you’re looking for an engine swap that gives you the most possible power, this isn’t it. Sure, it’s more powerful than the stock engine, but there’s no doubt that you can get more horsepower from an LS engine if that’s your goal.
Mazda 13B-REW
Engine Code: 13B-REW
Layout: Inline 2-rotor (rotary engine)
Displacement: 1.3 L (1,308 cc equivalent)
Fuel System: Multi-port fuel injection
Cylinder Bore: N/A (rotary design)
Piston Stroke: N/A (rotary design)
Compression Ratio: 9.0:1
Power: ~276 hp @ 6,500 rpm (JDM spec)
Torque: ~231 lb-ft @ 5,000 rpm
Firing Order: Sequential rotary ignition
If you don’t want to stray too far from the RX8’s rotary roots, then the 13B-REW from the FD RX-7 is an excellent swap option.
It’s as close a fit you can get to the original Renesis motor. You won’t have to worry about fabricating custom engine mounts, no frame modding will be needed, and it’ll have little to no impact on your handling.
This might be the cheapest RX8 engine swap out there, but there’s really no such thing as a cheap engine swap. Like the LS RX8 engine swap, the REW swap has the notable advantage of having more than a few kits on the market to help you get the job done.
This means less custom fabricating on your end and a more consistent experience when you’re swapping the engine.
The best part is tha you won’t have to touch the wiring for this swap. You can simply let your stock ECU run the power steering and gauges, and get a piggyback ECU like an adaptronic to run the engine.
Note that the 13B-REW has two turbos that likely won’t fit in the engine bay. Depending on the size of the turbo you want to run, you’ll require either a top-mount or bottom-mount turbo manifold; top-mount is ideal for clearance.
You’ll also need a tubular lower intake manifold because the stock cast one will not fit, or you can use one from a 20B, chop the extra runners off, and port match it to the new REW.
Alternatives and Common Concerns
Adding more power isn’t always the main motivator behind this upgrade. Many engine swaps are done out of necessity.
If you’ve got your hands on an RX8 with a blown motor and you’re looking for the cheapest way to get it back to running condition, your best bet is a new 13B-MSP block from Mazda.
The RX8’s reliability has always been questionable due to the terrible quality of third-party remanufactured engines installed in Series 1 cars. However, Mazda no longer has those remans, and so buying a new block straight from the source is a non-issue.
Interestingly the 2.0l MZR LF-VE motor from the NC Miata is also an option since the Miata subframe bolts right into the RX8. However, the RX8 firewall won’t clear it without substantial chopping and welding.
Then there’s the question of horsepower.
You’re better off with the OE motor if power is all you want; it’s a swap that has no gain unless you boost it, and if you do so, you’ll likely have to make a custom turbo kit in order to exceed what your Renesis motor makes from the factory.
Lastly, for anyone concerned about heavier engines throwing off balance and agility, there’s good news.
The RX8’s subframe is designed in a way that sits 95% of the engine behind the steering rack, so it can take a decent amount of extra weight.
The rest can be corrected by experimenting with spring rates, sway bars, and coilovers in order to fine tune your suspension geometry.
Would you ditch the dorrito in favor of a more reliable motor? Let us know by leaving a comment below!