NB Miata
Let’s face it—while the NB Miata is a joy to drive, its stock power leaves a bit to be desired. For car enthusiasts craving more adrenaline and horsepower, turbocharging is the perfect way to transform the Miata from a nimble roadster into a true performance machine. The thrill of adding a turbo to your Miata can turn every twist of the throttle into a surge of power that the stock setup simply can’t deliver.
This guide will walk you through everything you need to know about turbocharging your NB Miata. Whether you’re aiming for a modest boost of 200 horsepower or want to push the envelope closer to 250, this article will cover essential steps to make your build powerful, reliable, and cost-effective.
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Before diving headfirst into turbocharging, you need to ensure your Miata’s engine is in good mechanical health. Turbocharging an engine that isn’t ready for the increased power is a recipe for disaster. The last thing you want is to boost an engine that’s on the verge of failure, so let’s begin with some critical pre-build checks.
The first step in preparing for a turbo build is performing a compression test. This test will tell you whether the cylinders in your engine are performing as they should. Consistent compression across all cylinders is crucial because turbocharging places extra stress on the engine’s internals. To perform a compression test, start by disconnecting the fuel system to prevent fuel from entering the engine. Remove the spark plugs, then insert a compression gauge into each cylinder, cranking the engine for 3-5 seconds per cylinder to record the PSI readings. Ideally, you’re looking for readings above 170 PSI, with less than a 10% variance between cylinders. Anything lower or inconsistent could mean your engine isn’t healthy enough for a turbo setup.
Once the compression test checks out, take your Miata to a dyno to get a baseline reading of its current power output. Even if the numbers are low, don’t worry. What matters more is that the power delivery is smooth and that the engine isn’t misfiring or showing any signs of trouble. A healthy, smooth-running engine is key to ensuring your turbo build goes off without a hitch.
Knowledge is power—especially when it comes to turbo builds. Spending time reading up on the internet will give you valuable insights into the specific challenges and benefits of turbocharging a Miata. You’ll discover different turbo setups, common issues people have faced, and the most cost-effective ways to complete your build. Reading other enthusiasts’ experiences can save you from making costly mistakes and provide you with DIY solutions to save money. Remember, there’s no such thing as too much research when planning a turbo build. The more prepared you are, the smoother your project will go.
Proper engine management is the backbone of any successful turbo build. Without the right tuning and monitoring, you risk running your engine too lean or too rich, both of which can cause serious damage. In this phase, we’ll cover the essentials of managing your turbocharged Miata’s air-fuel mixture and ignition timing.
One of the most critical tools in a turbocharged Miata is a wideband air-fuel ratio (AFR) gauge. This gauge monitors the ratio of air to fuel that your engine is running, and keeping that ratio in check is vital to avoid blowing your engine. Running too lean (too much air and not enough fuel) can cause dangerous knock or detonation, while running too rich (too much fuel) will waste gas and slow you down. Brands like AEM and Innovate offer reliable wideband gauges that can help you monitor your engine’s AFR in real-time, ensuring you’re always running in the sweet spot.
To properly manage the increased air and fuel demands of a turbocharged engine, you’ll need a standalone ECU like Megasquirt. The stock Miata ECU isn’t equipped to handle the complexities of forced induction, and without upgrading to a standalone system, you risk running into all kinds of tuning headaches. The beauty of Megasquirt is its ability to give you full control over the engine’s fuel delivery and ignition timing, which are critical when running a turbo.
Start by installing the Megasquirt ECU while your car is still naturally aspirated. This allows you to familiarize yourself with tuning the ECU before the added complexity of a turbo. You can use the base map that comes with the Megasquirt to get your car running smoothly at stock power. Learning to tune on an NA engine gives you more room for error and helps prevent catastrophic mistakes once you add the turbo. While Megasquirt is a popular choice for its balance of cost and functionality, other options like Hydra or ECUMaster are worth considering if you’re looking for different features.
A turbocharged engine demands more fuel to keep up with the additional air being forced into it, so upgrading your fuel system is crucial. Without sufficient fuel, you risk running lean, which can lead to engine failure.
One of the best budget-friendly upgrades is swapping out your stock injectors for RX8 injectors. These injectors provide the extra fuel your engine needs without requiring major modifications. They fit directly into the stock fuel rail, making the installation process relatively straightforward. To install them, disconnect the battery, relieve fuel pressure by pulling the fuel pump relay, and remove the fuel rail and stock injectors. Once the RX8 injectors are in place, be sure to adjust the injector flow rate in your Megasquirt ECU to accommodate the larger injectors.
While the stock Miata fuel pump can handle up to around 300 horsepower, anything beyond that will require an upgrade. Popular aftermarket options like the Walbro 255 or Deatschwerks DW300 provide the extra fuel flow needed for higher horsepower builds. Installation involves dropping the fuel tank, removing the stock pump, and swapping it for the upgraded unit. After installation, check for any pressure drops at higher RPMs to ensure everything is working smoothly.
Now for the fun part—bolting on the turbo! This section covers how to choose the right turbo and supporting components for your build, as well as some installation tips to make the process smoother.
The heart of any turbo build is, of course, the turbocharger itself. When choosing a turbo, you’ll have to balance performance, reliability, and cost. A quality turbo like a Garrett GT2560R is more expensive but offers excellent reliability and longevity. On the other hand, while cheap eBay turbos may be tempting, they often suffer from premature failures and inconsistent performance. Stick with well-known, reputable brands for the best long-term results.
The exhaust manifold is where the turbo is mounted, and it’s a critical part of the system. Cast iron log manifolds are a reliable and budget-friendly option for turbocharging your Miata. While they don’t flow as well as tubular manifolds, they’re much less prone to cracking. When installing, make sure the manifold and downpipe are properly fitted, and be on the lookout for clearance issues, especially around the heater core lines.
Turbocharging compresses air, and compressed air heats up quickly, which can lead to detonation if it’s not cooled properly. This is where the intercooler comes into play. A front-mount intercooler (FMIC) setup is the most common choice for turbocharged Miatas. To install it, secure the intercooler with custom brackets and route the piping from the intercooler to the throttle body. Mocking up the piping before installing the turbo can save you time and frustration later.
A blowoff valve (BOV) is optional, but it helps improve drivability by reducing turbo lag and protecting the turbo from pressure spikes when the throttle closes. While not necessary for a basic build, a BOV can make your turbo Miata feel more responsive and help prolong the life of your turbocharger.
As you increase power, your Miata will generate more heat, so it’s vital to keep engine temperatures under control. Upgrading the cooling system and spark plugs will help maintain reliability and prevent overheating.
One of the most important cooling upgrades you can make is swapping out the stock radiator for a larger, more efficient unit like a Mishimoto radiator. This will help keep temperatures in check, especially during long pulls or track days. For added cooling efficiency, consider a 949 Racing coolant reroute, which helps cool the rear cylinders that often run hotter than the front ones.
Pro Tip: Overheating is one of the biggest threats to a turbocharged engine. Make sure you invest in proper cooling components to avoid costly damage down the road.
Turbocharged engines require colder spark plugs to prevent pre-detonation, which can be caused by the higher combustion temperatures under boost. Moving from the factory NGK heat range 5 spark plugs to NGK heat range 7 plugs is a smart move. Additionally, you may need to reduce the spark plug gap slightly, depending on your boost levels, to prevent misfires under load.
With the increase in horsepower and torque from your turbo, the stock drivetrain components may struggle to handle the power. Upgrading the clutch, transmission, and differential ensures your Miata can handle the newfound performance.
The stock Miata clutch will likely start slipping once you pass 140-150 wheel horsepower, so an upgrade is a must. A Flyin’ Miata Stage 1 or ACT Street clutch offers the durability needed to handle the increased torque of a turbocharged engine. While you’re at it, consider installing a lightweight flywheel, which will improve throttle response and make the car feel even more responsive.
If you’re running a 1.6L Miata, upgrading to a 1.8L torsen differential or a Ford 8.8 differential is a great way to ensure your drivetrain can handle higher power levels. While the stock 5-speed transmission can handle up to around 250 horsepower, anything beyond that will benefit from upgrading to a 6-speed transmission or a MazdaSpeed Miata transmission for added durability.
A turbo needs oil to function, which means you’ll need to modify the oil pan to add an oil return line. This step can seem intimidating, but with a few precautions, it’s straightforward.
The oil return line sends oil back to the pan after it’s been through the turbo. Drilling into the oil pan may sound scary, but it’s a necessary part of turbocharging your Miata. First, grease the drill bit to catch metal shavings, preventing them from falling into the pan. Wrap the drill bit with electrical tape to avoid drilling too deep, which could damage the oil pickup. Once you’ve drilled the hole, tap it for the oil return fitting, being careful to use grease to trap any remaining shavings. After drilling, drain the oil and flush the pan with mineral spirits to remove any leftover particles, then refill the oil before starting the engine.
After all the hard work, it’s finally time to start the engine and take your newly turbocharged Miata for a spin!
Before hitting the road, there are a few things you need to check to ensure everything is working properly. First, check for oil pressure immediately after starting the engine to avoid damaging the turbo. Next, inspect the engine bay for any oil or coolant leaks from the turbo lines. Finally, listen to the engine and make sure it’s idling smoothly without any unusual noises or rough running.
Once you’re sure everything is in order, take the car for a gentle test drive. Avoid pushing the car into full boost on the first drive, as you’ll want to give everything time to settle and check for any potential issues. Keep an eye (and ear) out for unusual noises, smells, or leaks, and take things slow. Rushing into full boost too soon can lead to problems that could have been easily avoided with a more careful break-in period.
Once everything is installed and running smoothly, it’s time to get your car professionally tuned. This is the final step in ensuring your turbocharged Miata runs at peak performance.
Proper tuning is essential to extract the best performance from your turbo setup. Find a tuner who specializes in Miatas or Megasquirt systems to ensure the air-fuel ratio, ignition timing, and boost levels are dialed in perfectly. A professional tune not only maximizes power but also ensures reliability, helping you avoid engine-damaging knock or detonation.
Megasquirt has an excellent overboost protection feature that cuts spark if your boost levels exceed a certain limit. Setting an overboost protection limit ensures that accidental over-boosting won’t damage your engine. This safeguard is especially helpful during the early stages of tuning when boost control may not be perfectly dialed in yet.
Here’s a rough estimate of the total cost for a basic turbo build:
Turbocharging your NB Miata is a thrilling and rewarding project that can completely transform the driving experience. However, it requires careful planning, quality components, and attention to detail to get right. Balancing power, reliability, and cost is key to making the most of your build. From initial research to the final tune, each step plays a crucial role in ensuring your car performs at its best. With the right preparation, you can avoid costly mistakes and enjoy the benefits of turbocharging your Miata for years to come.
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