Mazda 13B Tuning

"All you need to know about tuning the Mazda 13B engine!"

The Mazda 13B make awesome project engines and with a few sensible tuning upgrades like a remap, turbo kits and porting you will noticeably maximise your driving pleasure.

The big advantage of a rotary engine is that it can enjoy much higher speeds without being subject to the same internal forces as a reciprocating engine, and feels like it will rev to infinity and beyond!

Our aim here is to review 13B tuning and outline the best mods that work.

History, Power & Specs of the 13B Engine


  • 1984–1985 Mazda HB Luce
  • 1984–1985 Mazda HB Cosmo
  • 1984–1985 Mazda FB RX-7 GSL-SE


  • 1986–1988 Mazda FC3S S4 RX-7, 146 hp (109 kW)
  • 1989–1991 Mazda FC3S S5 RX-7, 160 hp (119 kW)
  • 1986–1991 Mazda HC Luce Turbo-II, 185 hp (138 kW)
  • 1986–1988 Mazda FC3S S4 Turbo RX-7 Turbo-II, 185 hp (138 kW)
  • 1989–1991 Mazda FC3S S5 Turbo RX-7 Turbo-II, 200 hp (149 kW)


  • 1990–1995 Eunos Cosmo, 235 hp (175 kW)


  • 1992–1995 Mazda RX-7, 255 hp (190 kW)
  • 1996–1998 Mazda RX-7, 265 hp (198 kW)
  • 1999–2002 Mazda RX-7, 280 hp (209 kW)

13B-MSP (Multi-Side Port)

The Renesis replaced the Wankel  and offered (211–235 hp) giving about 50% more efficiency over the previous design.

  • 2003- Mazda RX-8 157–175 kW (211–235 hp)

Tuning the Mazda 13B and best 13B performance parts.

Chart showing an RX8 tuned to various power levels and the resulting quarter mile times.

Horse Power
Quarter mile
200 1400 15.28
220 1400 14.82
240 1400 14.41
270 1400 13.87
300 1400 13.41
200 1200 14.54
220 1200 14.1
240 1200 13.71
270 1200 13.2
300 1200 12.77

Best 13B modifications

Just because particular upgrades are popular with 13B owners it doesn't mean its worth having, instead we'll concentrate on the top upgrades that will give your 13B the best power gain for you spend instead of falling into the "if it's shiny and makes more noise it must be good" thinking of many car sites and mags.

Rotary engines are a world of difference to the reciprocating piston engines and the approach to tuning is significantly different.

The 13B-REW shows how much potential there is and it's setup and design makes a good blueprint for upgrades on other non twin turbo setups.

They rotate at high speeds so focusing on air flow, and adding more fuel and increasing the air flow are the way to go.

Porting and polishing the B13 and upgrading the intake are priorities to get as much air into the engine as possible.

The rotors can be lightened, which allows them to spool up more quickly, it reduces wear and tear especially on the bearings and it helps smooth out the power band. A rotor should always be balanced after lightening.

The clearance between the edge of the rotor and cylinder wall needs careful attention, interestingly the factory tolerances improved as the engine evolved, particularly after 1989.

When performing machine work on the rotor you'll focus on the tip area especially on high horsepower applications where the additional stresses increase the risk of contact with the side housings.

Then attention is focussed on the face itself, where the surface is honed to fine tolerances and this removal is matched on the gear and non gear side of the rotor, along with work on the gear itself.

Turbo rotors are by design, stronger than the NASP rotors but they can be lightened. We've seen some benefits from fitting a lighter flywheel to the earlier engines, this is something Mazda did on later models anyway, and it frees up the engine to respond to rev changes more efficiently.

For a car driven daily, really you should, ideally aim to match your power band to your preferences.

Reducing the weight of the flywheel to around 9 lb's seems to be a popular choice and does change the nature of the engine quite a bit, but we should add not always to the taste of drivers, try one fitted to an RX8 first before you commit yourself here.

13B ECU remapping

The ECU mapping and injectors and fuel pump also have a large bearing on the power gains you'll make. The most common ECU setup we see on these is the  BBR DIY StarChip, A’pexi Power FC or Pettit racing, depending on your power requirements.

Aftermarket ECU's allow you to fine tune the timing and fuel delivery for the maximum power gain and this will also allow you to factor in any other mods you have done.

Avoid piggyback solutions, these just don't play nicely with the OEM ECU which sees something is "wrong" and backs things off. If you go to a specialist and get the car mapped you won't be disappointed.

On a standard car with an aftermarket engine management system, you can see power gains of around 5-10%.

The stock ECU generally sets the boost limit at 10lbs so an ECU upgrade is quite an early mod required on a serious 13B project.

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Best Engine Mods for your Car

    1. Mapping - remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
    2. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
    3. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
    4. Port work - The goals of porting and flowing the intake are to get air flowing into the engine while removing flow restrictions and turbulence.

    So we will break these usual recommendations down and see if these 'best mods' are appropriate for your car and we shall look in detail at the mods that will work for you and your needs.

Typical stage 1 mods often include:
Intake manifolds, drilled & smoothed airbox, Sports exhaust header/manifold, Remaps/piggy back ECU, Panel air filters Porting and gas flowing.

Typical stage 2 mods often include:
high flow fuel injectors, port enlargement, porting and polishing, induction kit, Sports catalyst & performance exhaust, fuel pump upgrades.

Typical stage 3 mods often include:
Twin charging conversions, Internal engine upgrades (port flowing/bigger valves), Engine balancing & blueprinting,  Upgrading forced induction (turbo/supercharger).

Carefully think through your options and then buy your mods and set yourself a power target to avoid wasting your time and money.

ECU flashing should help to unlock the full potential of all the upgrades you've done to your 13B .

(In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)

It will usually give you around 20% more power on turbocharged vehicles, but power output often differs on the upgrades you've done and the condition of your engine.

13B intake mods

It is vital to any engine upgrade project to push air and fuel into the 13B engine

Intake manifolds transmit the air during the suck phase from the filter and allow it to be pulled into the engine cylinders with fuel for the squish phase.

Usually the design and rate of flow of the Intake manifold can make a noticeable effect on fuel & engine efficiency and thankfully Mazda did a great job with the 13B intakes.

Many mass produced engine air intake manifolds are improved through motorsport parts, although some makers provide reasonably good air intake manifolds as is the case here.

In fact there are few induction kits that make power gains, with the very best sited in a cold air feed providing a 3-5hp boost at the top end! Not really worth the hassle and cost involved.

Port mods on the 13B

On the 13B actually enlarging and flowing the engine ports can make a dramatic difference, if supported with more air and fuel.

When you start tuning a rotary engine, you'll be increasing the internal engine speeds, spool up times and heat generated, this requires a fresh look at oil supply. We often see dry sump oil systems installed on these to accomplish this.

Seals around the engine rotors also need to be perfect if you are serious about increasing power. Instead of going with oversized seals make sure the rotor is perfectly flat, and this requires a specialist as most machine shops will not be able to work to the tolerances required.

Seals will fail if they are not mating with a flat surface or mounted on a level surface. It is a question of when not if, and is probably one of the biggest factors in engine problems.

Gear walk can be an issue on rotary engines. Before 1985 Mazda used 9 pins, and after this they increased that to 12 pins, but on highly tuned engines you can still suffer from gear walk.

Aftermarket tuners have come up with innovative methods to prevent the rotors gear separating from the body of the rotor at high RPMS and with high engine temperatures.

Mazda 13B Turbo upgrades

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes impressive power gains.

4 port engines are, we find, better suited to turbochargers than the 6 port ones but both conversions require a lot of work and planning and we would not recommend undertaking this unless you have obtained a full kit and have facilities to set up and create a custom map.

A swap with tubocharged 13B is probably the best route (quickest, cheapest and most reliable) to get forced induction on a NA (naturally aspirated) engine.

The stock turbo on the 13B are generally very capable units and can deliver around 15lb of boost which is good for around 350hp.

Whilst a stock twin turbo setup can run to around 15psi when setup correctly you'll need to look to aftermarket turbos to increase this. On the single turbo setups the requirements come on sooner as a single turbo will not have much more potential power to be released.

Big capacity turbochargers will usually suffer from no power at low rpm, and smaller turbochargers spool up really quickly but won't have the high rpm engines power gains. So with a rotary engine you need as much low end power as you can get so we'd avoid large turbos.

Instead a hybrid turbo (uprated internals in a standard case) or a twin turbo setup. Interestingly the FD3S has a two stage turbo setup with the larger turbo coming on stream at around 4600rpm.

Thanks to new tech the market of turbochargers is always increasing and we are seeing variable vane turbochargers, where the vane profile is altered according to speed to lower lag and increase top end bhp and torque.

It is common that there is a limit in the air flow (MAP) sensor on the 13B when considerably more air is being drawn into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped performance at a much lower level.

Get an uprated intercooler to save the power lost by heat gains. If you are serious about power gains then lose the air conditioning and fit a larger intercooler mounted at an angle in the engine bay. The intercooler will benefit from a bonnet vent if possible.

Adding a supercharger or additional turbo will make large bhp and torque gains, although more challenging to get working. We have this guide to twinchargers if you want to read more.

13B Fuelling Upgrades

Don't omit to look at the fuel delivery when you are increasing the torque - it makes the car more thirsty.

Mazda used 3 injectors per rotor, a total of 6 in early engines, then the later ones had 4 per rotor, 8 in total, so fuel delivery is fairly well cared for.

We see sharper throttle response from an upgrade on the fuel pressure regulator.

It makes sense to over specify your injector capacity and this goes for the fuel pump as well.

The rule of thumb is to add 20% to the flow rate when specifying an injector, which takes into account injector deterioration and provides some spare capacity should the engine need more fuel.

Bosch and Tomei fuel systems are popular on RX7 projects and for good reason, they also cope well with the fuel requirements at 13lbs or more of boost quite capably.

We think this one is common sense, but you'll need to match your fuel injector to the type of fuel your car uses as well.

13B Performance Exhausts

Only look to replace your exhaust if the existing exhaust is actually causing a restriction in flow.

On most factory exhausts you'll find the exhaust flow rate is still fine even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

The 13B exhaust gets very hot and in some race situations the exhaust has been known to increase in length by a surprising amount, so quality counts here. Getting  a cheap exhaust is a false economy as it just won't last.

Do not go with the widest exhaust you can source this will reduce the exhaust flow rate - the best exhausts for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Typically exhaust restrictions are traced to the catalyst and filters installed, so adding a freer flowing race alternative such as a sports catalyst pretty much removes this restriction, thanks to it's larger size and surface area, and will effectively raise the performance to levels you would expect without having a catalyst installed, but keeps the car road legal.

Weak spots, Issues & problem areas on the 13B

The 13B engines are generally reliable and solid as long as they are very regularly serviced and maintained. The 13B does require a LOT of care and attention.

Oil leaks have also been reported but a number of specialist RX7 tuners offer stronger sumps with a better o ring seal.

Regular oil changes are vital on the 13B , especially when tuned and will help extend the life and reliability of the engine.

Make sure the fuelling is spot on, many engines have met an early demise because they have been running to rich or too lean

Ignition coil failure is common, primarily because these work really hard. Keep an eye on oil consumption and frequently renew the oil, a rotary engine will use more oil than most conventional motors.

Check the compression of your engine, it's a good way to spot potential problems before they get too expensive, and if buying an RX8 I would insist on a compression test before I handed over any money.

If you would like to know more, or just get some friendly advice on Tuning your 13B engine please join us in our car forums where you can discuss 13B tuning options in more detail with our 13B owners. It would also be worth reading our unbiased Mazda tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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