Why the Garrett G20 Turbo Is a Smart Upgrade for Your NA Miata

The Mazda MX-5 Miata (NA generation) is beloved for its nimble handling and lightweight chassis, but its 1.6L or 1.8L engine lacks the power to match. Adding a turbocharger transforms the car without ruining its character. The Garrett G20 turbo (a GT2560R variant optimized for smaller engines) offers quick spool, excellent mid-range torque, and a proven track record. This guide covers a complete installation, from preparation to tuning considerations, so you can enjoy a reliable 180–220 whp setup on your stock bottom end (with proper fuel and tuning).

Tools and Materials Needed

Gather everything before you start. A well-organized workspace reduces frustration and prevents mistakes.

  • Garrett G20 turbocharger (GT2560R journal bearing, .64 A/R turbine housing)
  • T3/T25 flanged exhaust manifold (cast iron or tubular, specifically for NA Miata)
  • Wastegate (internal on G20, or external if manifold requires it)
  • Intercooler: 2.5″ or 3″ core, bar-and-plate design (e.g., Flyin’ Miata, Bell Auto Sport)
  • Intercooler piping kit with silicone couplers, T-bolt clamps
  • Blow-off valve (optional but recommended for longevity)
  • Oil feed and return lines (braided stainless recommended)
  • Coolant supply and return hoses (for water-cooled G20)
  • Boost controller (manual or electronic)
  • Downpipe (2.5″ or 3″ with catalytic converter if needed)
  • Intake tube with filter (relocate MAF if using OEM ECU)

General Tools

  • Socket set (1/4″ and 3/8″ drive, metric – 8mm to 19mm)
  • Combination wrenches (10, 12, 14, 17, 19mm)
  • Torque wrench (ft-lb and in-lb)
  • Pliers, screwdrivers, and pry bar
  • Gasket scraper
  • Dremel or die grinder (for minor clearancing)
  • Jack and jack stands
  • Safety glasses, gloves, and shop rags

Consumables & Hardware

  • Exhaust manifold gasket, turbo gasket, downpipe gasket
  • New crush washers for oil lines
  • High-temp thread locker (Loctite 272 or 262)
  • Anti-seize compound
  • Coolant (50/50 mix)
  • Engine oil (for filling oil lines and post-installation)

Preparation: Safety and Access

Park on a level surface, allow the engine to cool completely, and disconnect the negative battery terminal. The NA Miata’s engine bay is tight; removing the radiator and hood is optional but helps access.

Disconnect Battery and Drain Fluids

Remove the battery negative terminal. Drain the engine oil and coolant if you plan to replace them (recommended). This minimizes mess when connecting oil and coolant lines later.

Remove Existing Components

Clear the engine bay to make room for the new hardware. Work methodically and label bolts.

  • Remove the factory air filter box, snorkel, and intake tube.
  • Unbolt the factory exhaust manifold. Soak studs with penetrating oil before wrenching.
  • Disconnect the O2 sensor from the manifold (careful with wires).
  • Remove the heat shield on the exhaust manifold.
  • If you have a 1.6L, you may need to remove the upper intake manifold for better access – mark vacuum lines and wiring harness clips.
  • Remove the radiator fan shroud (or the whole radiator) to install intercooler piping more easily.

Installing the Garrett G20 Turbo

With the engine bay cleared, install the turbo system in a logical order: manifold, turbo, oil/coolant lines, intercooler, piping, intake, and finally the downpipe and exhaust.

Step 1: Install the Exhaust Manifold

Use a new manifold gasket. If you have a cast iron manifold, tighten evenly to 30–35 ft-lb. Tubular manifolds with a T3/T25 flange may require different torque – follow the manufacturer’s spec. Apply anti-seize to studs that could corrode.

Step 2: Mount the Garrett G20 Turbo

Use new gaskets between manifold and turbo. Align the oil drain port at the bottom, ensuring it clears the block. The G20’s .64 A/R turbine housing spools quickly on a 1.8L; on a 1.6L it’s still responsive. Tighten the flange bolts to 20–25 ft-lb. Verify that the wastegate actuator arm moves freely.

Step 3: Oil and Coolant Line Connections

Proper lubrication and cooling are critical. The G20 has both oil and water ports.

  • Oil feed: Use a -3AN or -4AN braided line from the oil pressure sender port (or a sandwich plate) to the turbo top inlet. Use a restrictor if oil pressure is high; typically not needed on a Miata.
  • Oil drain: Run a -10AN line from the turbo drain port to the oil pan (drill and weld a bung, or use a pre-tapped pan). Ensure the line has a gentle downward slope – no sharp bends.
  • Coolant feed: T into the heater hose or use a water pipe adapter. Consult a guide like Flyin’ Miata’s coolant routing diagram.
  • Coolant return: Return to the thermostat housing or lower radiator hose.

Use new crush washers at every banjo fitting. After connecting, temporarily plug the oil feed and rotate the engine by hand to prime the turbo – or pre-fill the oil lines before first start.

Step 4: Intercooler and Piping

The intercooler mounts in front of the radiator. For an NA Miata, you’ll likely need to trim the bumper support or remove the “mouth” brace. Support the intercooler with brackets or zip-ties initially, then secure with bolts through the bumper rebar.

  • Route hot-side piping from turbo compressor outlet to intercooler inlet.
  • Route cold-side piping from intercooler outlet to throttle body.
  • Use silicone couplers and T-bolt clamps; tighten evenly but not overly – silicone can bulge.
  • Avoid sharp bends near the throttle body; a 180° bend from the passenger side works well.
  • Install a blow-off valve on the cold side piping near the throttle body for best response.
  • If you have a 1.6L with a flapper door airflow meter, relocate or switch to a speed-density system – otherwise the blow-off valve will cause stalling. Megasquirt ECU is a popular solution.

Step 5: Boost Control and Wastegate Setup

The G20 comes with an internal wastegate. You can control boost with a manual boost controller (e.g., Turbosmart) or electronic one (e.g., EBC). Set initial base pressure to about 6 psi by adjusting the actuator rod length. For higher boost, you’ll need a stronger actuator spring or an external wastegate if you exceed 12 psi safely on stock internals.

Step 6: Intake and Filter

Install a high-flow intake tube from the turbo compressor inlet to a cone filter. Use a heat shield to reduce hot intake air temperature. If retaining the OEM ECU, keep the MAF sensor in the intake path (after the filter, before the turbo). For aftermarket ECUs, you can remove the MAF entirely.

Step 7: Downpipe and Exhaust

Bolt the downpipe to the turbo exhaust outlet. Use a new gasket. Route it down past the steering rack and connect to the existing exhaust (or a 2.5″ cat-back). A high-flow catalytic converter is recommended for street cars; de-cat may be used for track use (check local laws). Ensure the downpipe doesn’t hit the frame during engine movement – add a flex section if needed.

Reconnecting Electricals and Final Assembly

Reconnect the battery, but leave the ignition off. Refill engine oil and coolant. Check all connections: oil lines, coolant hoses, intercooler pipes, and electrical connectors (O2 sensor, MAF, ignition coils). Install the radiator and fan shroud if removed. Reinstall any plastic covers.

First Start – Pre-Prime the Turbo

Before cranking, crank the engine with the fuel pump fuse or relay disconnected (or disable injectors) for about 10 seconds to build oil pressure and fill the turbo lines. Then reconnect the fuse and start the engine. Let it idle, listen for odd noises, and watch for oil or coolant leaks. A small smoke cloud from the exhaust is normal (new gaskets burning off).

Testing and Tuning

Boost Leak Test

Use a boost leak tester on the intake pipe. Pressurize to 15 psi and listen for hisses. Common leaks: coupler clamps, throttle body gasket, PCV system. Fix before driving.

Check Oil and Coolant

After running a few minutes, shut off, check oil level, top off coolant. Look for drips under the car. Tighten any weepy fittings.

Test Drive and Tuning

Start with low boost (5–6 psi) for the first drive. Gradually increase load and monitor air-fuel ratio (AFR). A wideband O2 sensor is essential. Target AFR of 12.0–12.5 at full boost (gasoline). If using a pre-tuned ECU (e.g., Megasquirt with a base map), adjust fuel tables and ignition advance. If using the stock ECU, you must install a rising-rate fuel pressure regulator (RRFPR) or a piggyback like the Miataturbo.net community’s common setups – but for reliability a standalone ECU is strongly recommended.

Check for detonation under load (listen for pinging). Reduce timing if needed. The Garrett G20 on a stock NA Miata with proper fuel and intercooling can safely run 8–10 psi without internal engine upgrades. For higher power, consider forged rods, pistons, and a stronger clutch.

Conclusion: Enjoy the Transformation

Installing a Garrett G20 turbo on your NA Miata is a weekend job for a competent DIYer. The result is a car that retains its lightweight, flickable nature while gaining 70–100 hp. Pay attention to oiling, cooling, and tuning – these three pillars make the difference between a reliable build and a blown motor. For further reading, consult Garrett’s official G-series page and Flyin’ Miata’s tech section. Happy boosting!