Ultimate Mazda RX8 Mod Guide
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Ultimate Mazda RX-8 Performance Mods Guide

Jake Mayock

Meet Jake

Jake is a founder of 8020 Media and TuningPro. He has over a decade of experience in the automotive industry including parts sales, writing, DIY modifications & repairs, and more. Jake is currently converting his N54 to a single turbo and building a Miata track car. He’s an experienced, hands-on automotive enthusiast who delivers in-depth, well-researched content.

Despite the Mazda RX-8’s engine problems, it can be quite a fun little car to own and drive. What it lacks in power it makes up for in handling and quickness making it a fun street or track car for any car enthusiast. Low prices for used Rx8’s make it an affordable performance car for any budget.

I owned an RX-8 for 7 years and pretty much did everything to it except toss a turbo kit on it since I was a broke college kid. Which gets me to an important point: the Rx8 is an expensive car to modify and the power gains are a bit underwhelming without a turbo or engine porting.

But, every extra horsepower makes this car more fun to drive so I’m going to talk about every possible performance upgrade for the RX-8, including: intakes, tuning, headers, mid-pipes, cat-backs, flywheels, pulleys, engine porting, and turbocharger upgrades. This covers everything, except 3-rotor and LS-swaps, of course.

Ultimate Mazda RX8 Mod Guide

Mazda RX-8 Power Limits

On a dyno, a completely stock RX-8 will put down around 180-185whp and ~140wtq which is a bit depressing compared to the RX-7 predecessor.

A naturally aspirated Rx8 can produce around 225whp which is considered maxed out. Bolt-on mods can get you around the 210whp mark. Getting from the 210whp to 225whp mark is going to require some more expensive modifications like engine porting.

Anything above 225whp is going to required forced induction via a turbocharger. Reliability is somewhat okay at the 300whp mark but you probably don’t have more than 10,000-15,000 miles left in the engine at these power levels. 400whp can be achieved with a turbo but this will require a built motor and block upgrades.

So overall the RX8 engine isn’t very tuner friendly. For an engine that already lacks reliability adding power to it only makes it worse. Hitting the bolt-on power limits of ~210whp is rather costly and shooting for anything higher than that is extremely costly and highly unreliable. Also, the automatic versions are only 4-ports compared to 6-ports on the manual so they are even worse for power and performance.

Mazda RX-8 Performance Mods & Upgrades

  • Cold air intake
  • Flash tune / custom tune
  • Headers
  • Midpipe
  • Catback exhaust system
  • Lightweight flywheel
  • Pulleys
  • Intake & exhaust porting
  • Turbochargers & superchargers

1. Cold Air Intake Upgrades

Cold air intakes increase power by doing two things. First, they bring more air into the engine via a larger filter and removes the restriction created by the factory intake box. The increased air flow increases the pressure of the air within the intake system and combustion chamber which in turn creates more power. Secondly, it relocates the filter to a lower part of the engine so that colder air is sucked in. Colder air is more combustible which increases power as well.

However, since the RX8 is naturally aspirated the power gains achieved aren’t quite as impressive. Nonetheless, an upgraded intake will add about 3-4whp on the Rx8 when combined with a tune and other exhaust modifications. The stock intake on the Rx8 is actually pretty good so an intake alone with zero other mods likely won’t provide any power gains.

The alternative option to a full intake system is a K&N drop-in filter. Drop-in filters have shown to provide about 1whp gains. Since the cost of an intake system is quite expensive when compared to the power gains it provides we generally only recommend adding one if you plan on adding a tune and other bolt-on mods.

Benefits

  • 3-4whp gains
  • 1-2wtq gains
  • Cool intake sounds
  • Better throttle response

2. Flash Tune / ECU Tuning

A flash tune or ECU tune is going to be the best bolt-on mod for your RX-8 in terms of power gains. ECU tuning adjusts the fueling, timing, and various other engine variables to increase power and smooth out the power band. The best option on the market for the Rx8 is the Cobb Accessport.

The Accessport simply plugs directly into your OBDII port and re-flashes the ECU to increase power. It is plug-and-play and easily removable. It comes with a handful of base tunes on it made for various different power goals and existing modifications.

While every 13B Renesis comes with the same factory ECU, they don’t all have an optimal tune. Every engine is slightly different and therefore the factory tune interacts differently with every engine it is installed on. Some engines just aren’t tuned well initially. An Accessport tuner will adjust all of these variables to properly interact with your engine and create a smoother, more powerful, and more reliable engine.

Custom Tuning

While plugging a standard Accessport into your RX8 will result in some power gains, the best gains come from custom tuning. Adding mods impacts the way an engine works from fueling to AFRs, etc. The off-the-shelf tunes that come on an Accessport aren’t necessarily optimized for your engine and the mods you have made. Therefore, getting a custom tune is one of the best upgrades you can make with your Accessport.

I recommend only getting a custom tune once it is necessary based on your mods or once you are done adding mods to the car. Every new mod added adjusts the way your engine runs and therefore will require the custom tune to be redone. Pretty much all custom tuning shops will tune based off of the Accessport which is why it is the only tuner we recommend.

RX-8 ECU Tune Benefits

  • 8-10whp gains and similar torque gains
  • Improved power curve
  • Engine runs better and therefore is more reliable
  • Plug-and-play and easy to remove and adjust on the fly

3. Header Upgrades

Headers are the first component of the exhaust system. They bolt right up to the block and funnel exhaust gases to the midpipe which houses the catalytic converter. Headers on a completely stock RX-8 will purely be a sound mod as they don’t provide a whole lot of benefit to a stock engine. However, once you add a tune and an intake headers can provide some decent power gains when coupled with a full exhaust system.

Once more air is being funneled into the engine and more power is being created, more exhaust gas is also created. The stock headers become restrictive once more air and power are present. This creates additional backpressure in the exhaust system which can push exhaust gases back into the combustion chamber and throw off AFRs. An upgraded header reduces backpressure and therefore creates more power. Additionally, it lowers exhaust gas temps which are already hot enough on these engines.

There are two different options: short tube or long tube headers. Long tube headers will provide slightly better power gains but they will require an aftermarket midpipe. Short tube headers provide slightly lower power gains but bolt directly up to the factory midpipe.

One cautionary reminder: headers will made the Rx8 pretty loud. Especially when combined with a catless midpipe and a full exhaust system. I had a custom straight-piped exhaust on my Rx8 with stock headers and it was brutal. The rasp is crazy and there is nothing worse than having a 190whp car that sounds like it should have 1000whp.

Header Benefits

  • About 5whp gains with additional mods
  • Louder exhaust note
  • Reduced exhaust backpressure

4. Catless Midpipe Mods

The next part of the exhaust following the headers is the midpipe. The midpipe is the most restrictive part of the exhaust system because it houses the primary catalytic converter. If you are looking for power gains, the only option for upgrading the midpipe is to go with a catless midpipe. While this is technically illegal it does provide some power gains.

The stock cat does reduce a lot of noise which means removing it will make the car a good bit louder. Option A is to straight pipe it, which I don’t recommend with how loud this will make it. Option B is to get a midpipe with a single resonator. And the last option and best option for sound is to get one with dual resonators. The dual resonators will help reduce the raspy exhaust note caused by removing the cat. This will cause a P0420 engine code so you will need a Cobb Accessport or other tuning device to code out the CEL.

Catless midpipes are quite hard to find nowadays. The alternative option is going with a high-flow option. High-flow midpipes keep the catalytic converter but instead use one that is less restrictive than the stock cat. However, RX8 exhaust gas temps are extremely high and will eventually burn straight through the cat and therefore essentially make it catless. Since high-flow options have cats in them they will provide less power gains.

Catless Midpipe Performance Benefits

  • 5-7whp gains
  • Very minimal torque gains
  • Reduced exhaust backpressure
  • Louder exhaust note

5. Catback Exhaust Upgrades

A full header-back exhaust system will add about 12-13whp to the RX-8. The majority of these gains come from the headers and midpipe but the cat-back portion of the exhaust does add a few exhaust horsepower when combined with the midpipe and headers. A cat-back on a completely stock car is just a sound mod and won’t really provide any power gains.

Catback power gains come from further backpressure reduction. Since this part of the exhaust is the least restrictive to start with and the furthest away from the exhaust ports, it provides the smallest gains out of all the exhaust components.

When picking a cat-back exhaust system it really comes down to sound. They all do the same thing and provide just about the same power gains. TurboXS for example is the loudest possible exhaust on the market whereas brands like Racing Beat and Agency Power are a bit more modest.

Cat-Back Exhaust Performance Gains

  • 2-3whp gains
  • Limited torque gains
  • Less exhaust backpressure
  • Louder exhaust note

Ultimately, RX8 catback exhaust upgrades have some power gains and other benefits. However, modding the headers, midpipe, and catback can result in a very loud 13B. As such, you might consider only opting for one or two of these options and the headers and midpipe are where you’ll see the best power and performance.

6. Lightweight Flywheel Upgrades

Flywheels rotate along with the engine and provide rotational inertia when your foot isn’t on the accelerator. Without a flywheel if you took your foot off the accelerator the engine would stop spinning and die. The flywheel continues rotating when your foot is off the gas which keeps the engine spinning and running.

Upgrading the flywheel doesn’t necessarily create more power but it does improve acceleration and make your car quicker. Since the flywheel spins with the crankshaft it acts as a force going against the engine. Upgrading the flywheel and reducing its weight allows the engine to spin quicker and reach redline faster.

While it doesn’t add power, it does make the engine more responsive and reach redline quicker. An rx8 with a lightweight flywheel will dyno the same numbers as one with a stock flywheel, but it will likely reach 0-60mph faster. Since most people care more about how fast their car is vs. how much power it makes, this is a great mod.

The more weight you reduce from the flywheel the more responsive the engine will be. However, it does have some impact on drivability. Since the engine now revs up faster it also revs down faster which can make starting uphill more challenging.

Lightweight Flywheel Benefits

  • More responsive engine / throttle response
  • Revs faster
  • Improved acceleration

7. Lightweight Pulleys

Similar to the flywheel upgrade, upgrading the pulleys is a weight-reduction modification. The RX-8 has three different pulley systems: one for the crank, alternator, and water pump. Since all of these belts are driven by the crank, the idea behind upgrading the pulleys is by reducing the weight of the pulley wheels. Therefore there is less crankshaft force being applied to turning the pulleys.

The majority of RX8 pulley kits are underdrive pulleys. Under drive means that you are reducing the speed at which these pulleys rotate, slowing them down so that they use less horsepower from the crankshaft. So you are 1) reducing the weight of the pulley systems, and 2) slowing down how fast they rotate or move. The benefit is freeing up horsepower at the crank so that more power is put down to the wheels.

The downside to pulleys is that the weight reduction isn’t super meaningful, and they have negative implications on all of the systems they pull. Underdriving your AC system for example isn’t a big deal but underdriving the alternator is bad for the battery and electrical systems and underdriving the water pump can lead to overheating.

If you do want to upgrade your pulleys we recommend staying away from underdrive pulleys for your water pump as excess heat is really bad for rotary engines. A lot of RX8 owners recommend staying away from pulley upgrades, for what it is worth. The power gains are minimal and the risk to reliability doesn’t make it worth it, unless you want the cool look inside the engine bay.

Pulley Pros & Cons

  • 1-2whp gains
  • Faster throttle response
  • Improved acceleration
  • Underdrive is bad for battery and water pump
  • Weaker air conditioning
  • Worse power steering

8. 13B Renesis Intake & Exhaust Porting

Porting the 13B engine is similar to porting the heads on a piston engine. It involves making the intake and exhaust ports larger to improve airflow in and out of the combustion chamber. Porting an engine requires is to be completely disassembled as the ports are located on the rotor housings. Because of this it is quite expensive to perform since it requires the engine to be pulled, disassembled, and then put back together. However, if you already have your engine taken apart, porting it actually isn’t too expensive as it just requires some tooling to be done to the stock rotor housings.

Porting is an advanced topic that we don’t recommend for anyone that isn’t either chasing big power levels or using their Rx8 for racing applications. There are generally 3 different levels on 13B porting: street ports, bridge ports, and peripheral porting. Bridge ports and peripheral ports especially are predominantly used for high horsepower racing applications.

We aren’t going to get into too much detail here, so here is a good guide on the different porting options for the RX8.

We really only recommend porting your engine if it’s already being rebuilt, or if you already have forced induction and are still chasing more power. Turbo kits offer a better bang-for-the-buck than porting does in this case and therefore we recommend chasing that route first.

RX8 Porting Power Gains

  • Street Port: 15-25whp
  • Bridge Port: 30-40whp
  • Peripheral Port: 50-60whp

9. Turbocharger & Supercharger Kits

The real power gains for the 13B Renesis engine lie in forced induction. Getting a naturally aspirated RX8 beyond the 210whp mark is difficult and expensive. Forced induction is the easy route to significant power gains with turbo and supercharger kits capable of producing 300-400whp.

For those serious about forced induction, check out this thread. Turbo kits are more popular for the RX8 since there is really only one supercharger kit, manufactured by Pettit Racing which starts around $7k. Choosing to add a turbo requires a lot of knowledge and understanding of the 13B and forced induction. Since this is a pretty hefty topic, we are going to save the details for a separate RX-8 turbo upgrade guide.

The GReddy kit is probably the most popular kit available, and the cheapest starting around $5k. However, the downside is that the kit is only good for about 275whp. Other kits are available that can produce power levels in excess of 400whp.

Unless you have $10k+ sitting around to drop into your Rx-8, I would avoid thinking about a turbocharger. The kits are expensive and with supporting mods you likely aren’t going to build anything for less than five figures. On top of that, it has some major reliability considerations.

RX8 Performance Upgrades Summary

Overall, adding an intake, tune, and a full header-back exhaust system can provide 20-30whp. With a stock RX-8 dyno’ing in the 180-185whp range, you are looking somewhere in the ballpark of 200-215whp for a “full bolt-on” Rx8.

Add a street port onto the engine and you can expect to make around 230whp which is considered the top limit for a 13B engine without more aggressive porting or forced induction. Aggressive porting like a peripheral port can put down numbers around 260whp, but this is not a beginner-friendly mod nor is it cost effective. The biggest gains and most cost-effective gains come from the addition of forced induction.

275-300whp is a safe limit for the Rx8 when turbocharged, however, reliability at these power levels is still probably limited to about 10,000 miles. Going over 300whp is going to require upgrades to the block/rotor housings as well as numerous other internal improvements and upgrades.

At the end of the day, unless you have $10k+ to dump into this car, the best mods for the RX8 are probably suspension/handling, such as upgraded RX8 coilovers, and appearance related. As a guy who had a straight-piped RX8 trust me when I say you don’t want to be that guy with the loudest car on the road only putting down 200whp.

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2 Comments

  1. Very true about being loud and only having 200whp! Everyone wants a piece of you, and few of whom you can beat! Also every cop within ear shot is going to take notice

  2. One thing to note. In 2006 mazda switches to the 6 port engine in automatics as well. The reason for the lack of power is the stock transmission would get too hot after 7500 rpm. So the 2006+ auto’s make 20hp less due to the red line difference making 212hp at 7500rpm. Manual makes 232 at 8500rpm. Both make the same power up to 7500rpm

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