The Garrett G42 Turbo: A Detailed Overview for Supra Owners

For decades, the Toyota Supra has stood as a benchmark for inline-six performance and tuning. Whether you own a MKIV with the legendary 2JZ-GTE or a MKV with the B58, the path to serious horsepower often involves a turbocharger upgrade. Among the many options available, the Garrett G42 has emerged as a favorite for enthusiasts who want a blend of spool, peak power, and durability. The G42 sits in a sweet spot between smaller frame turbos like the Garrett G35 and larger units such as the G47, making it one of the most versatile choices for a streetable 600-900 horsepower Supra.

In this comprehensive guide, we will break down the Garrett G42’s design, real-world power gains, required supporting modifications, and the reliability considerations that come with pushing a Supra to these power levels. By the end, you will have a clear roadmap for a successful upgrade.

Why Choose the Garrett G42?

Garrett Advancing Motion has a long history of producing performance turbochargers for OEM and aftermarket applications. The G42 is part of their G-Series line, which introduced a number of engineering improvements over the previous GT and GTX generations. The key advantages include:

  • Advanced Aerodynamics: The compressor wheel uses extended tip technology to improve flow and efficiency across a wide operating range.
  • Forged Milled Wheels: Both the compressor and turbine wheels are machined from solid billet, providing superior strength and balance.
  • Dual Ball Bearing Core: Reduces friction and allows faster spool, combined with oil and water cooling for extended life.
  • Cast Turbine Housing: Available in multiple A/R options (0.83, 0.92, 1.06) and inlet flange configurations (T3, T4, V-Band), letting you tailor the setup to your engine and goals.

Compared to the Garrett G35, the G42 moves up from a 65mm compressor to a 71mm wheel, which unlocks roughly 100-150 additional horsepower. Against the larger G47, the G42 retains faster transient response, making it a better choice for daily driven cars or road course use where immediate power delivery matters.

G42 Key Specifications

  • Compressor Inducer Diameter: 71mm
  • Turbine Inducer Diameter: 62mm
  • Compressor Outlet: 4.0” anti-surge ported shroud
  • Turbine Housing: Cast iron, available in 0.83, 0.92, and 1.06 A/R
  • Maximum Boost Pressure: 30 psi (2.07 bar)
  • Maximum Flow Rate: 80 lb/min
  • Horsepower Range: 600–900 hp (depending on fuel and supporting mods)

These figures confirm the G42’s ability to support serious power, but the real question is how it performs on a Supra.

Real-World Power Gains on the Toyota Supra

The power you can achieve with a Garrett G42 depends heavily on your engine’s platform and the quality of supporting modifications. Below we break down typical results for a 2JZ-GTE, as this remains the most common application, though similar numbers are possible on a MKV B58 with a well-thought-out setup.

Power Level 1: Bolt-On Support (600-650 hp)

With a completely stock 2JZ-GTE engine, a Garrett G42 on a 0.83 A/R T4 twin-scroll housing can produce around 600-650 whp on pump gasoline (93 octane). This requires:

  • Upgraded fuel injectors (1,000 cc/min or larger)
  • A high-flow fuel pump (450 lph or dual Walbro 255s)
  • A front-mount intercooler (minimum 4” core)
  • A 3.5” downpipe and full exhaust
  • A standalone ECU with professional tuning

At this level, the factory internals are still relatively safe if the tune is conservative and boost is kept around 18-22 psi. Many owners stop here for a reliable street car that can still surprise exotics.

Power Level 2: Head Studs & Port Fuel (700-750 hp)

If you want to push toward 700-750 whp, the factory head gasket and factory head studs become marginal. A common upgrade is to install ARP head studs and use a multilayer steel (MLS) head gasket. Additionally, the fuel system should be upgraded to include:

  • Larger injectors (1,600 cc/min or 2,000 cc/min for E85)
  • A dedicated fuel pressure regulator with -8AN feed line
  • An upgraded fuel rail

On E85 fuel, the G42 can achieve 750 whp at around 25 psi with the 0.92 A/R housing. The car remains very responsive thanks to the quick spool characteristics of the twin-scroll setup.

Power Level 3: Built Engine & Race Fuel (800-900 hp)

For the enthusiasts seeking the upper limit, the engine must be fully built with forged pistons, billet rods, and a billet main girdle. With a 1.06 A/R housing and race fuel (or P100), the G42 can flow enough to reach 850-900 whp at 28-30 psi. At this power level, a high-quality intercooler with a proper air-to-air or air-to-water system is mandatory, along with a large exhaust and a purpose-built oil system to handle the heat.

It is worth noting that the G42 is not a 1,000 hp turbocharger by itself; if you want to go beyond 900 whp, a G47 or a custom T6-frame turbo would be a better choice. For the majority of street-driven Supras, though, the G42 offers the best blend of tractability and top-end muscle.

Reliability Considerations: A Deep Dive

Power gains are exciting, but reliability must be planned from the beginning. The Garrett G42 itself is a very robust unit, but the overall reliability of the system depends on how well the supporting components and engine management are executed.

Engine Limits: The 2JZ-GTE

The stock 2JZ-GTE is famously strong, but that strength has limits. The factory connecting rods are cast and will bend around 650-700 whp. The factory head gasket and head bolts also become a weak point at elevated boost pressures. If you plan to run more than 600-650 whp, plan on:

  • ARP 2000 or L19 head studs
  • Cometic or Toyota OEM MLS head gasket
  • A properly decked block and head

For 800+ whp, the rods and pistons must be replaced with forged units. Many builders recommend a stock bore with forged internals to maintain block strength. Additionally, the main bearings and oil pump should be upgraded to a billet gear unit to ensure consistent oil pressure under high-rpm loads.

Oil System Management

The G42 turbocharger requires a clean oil supply and a properly sized drain to prevent pressure building up in the center housing. Some common issues arise from:

  • Insufficient oil return: The drain line must have a free flow and slope downward from the turbo. On a 2JZ, the oil pan often needs a dedicated -10AN or -12AN return fitting.
  • Oil pressure: The G42’s journal bearings (dual ball bearing) need a restrictor. Many install an oil feed restrictor with a 0.035” or 0.045” orifice to keep pressure below 30-40 psi at the turbo inlet.
  • Crankcase pressure: High power Supras should have a good crankcase evacuation system (catch can with vacuum source) to prevent oil from being pushed past the piston rings.

Cooling and Heat Management

Heat is the enemy of both the engine and the turbo. When upgrading to the G42, ensure that:

  • The intercooler core is sized appropriately. A 4” thick bar-and-plate core with full ducting is recommended for 700+ whp.
  • A high-flow radiator (e.g., 3-row or dual pass) and electric fans are in place. Many track-driven Supras also benefit from an oil cooler with a thermostat.
  • The exhaust manifold is wrapped or ceramic coated to reduce underhood temperatures. This keeps the turbo housing cooler and helps prevent heat soak.

Boost Control and Tuning

Proper tuning is non-negotiable. The G42 can spool quickly, and without good boost control it can overshoot target, potentially damaging the engine. Use a single-stage or three-port boost control solenoid, and have the car tuned by a professional with experience on the G42 platform. Key tuning parameters include:

  • Ignition timing: Conservative advance to avoid detonation, especially on pump gas.
  • Air-fuel ratio: Target 11.5-11.8:1 on gasoline, 11.8-12.2:1 on E85 under boost.
  • Boost by gear: Helpful for traction in lower gears.
  • Wastegate spring selection: Use a spring that allows at least 12-15 psi base boost. For a twin-scroll setup, a 0.83 A/R housing with an internal wastegate may be adequate; larger A/R housings often require an external wastegate (Tial 44mm or 46mm) for better boost control.

Supporting Modifications Checklist

To ensure your G42 upgrade is reliable, address these components before final tuning:

  • Fuel System: Injectors (1,600-2,000 cc/min for E85), fuel pump (450+ lph), pressure regulator, stainless lines.
  • Intake System: 4” or 5” cold-side piping, high-flow air filter, silicone couplers with T-bolt clamps.
  • Intercooler: Bar-and-plate core minimum 24”x12”x4” with short route piping.
  • Exhaust System: 3.5” or 4” downpipe, full 3.5” exhaust with a high-flow catalytic converter (if emissions required) or a test pipe.
  • Engine Management: Standalone ECU (e.g., AEM Infinity, Haltech, or MoTeC).
  • Drivetrain: At power levels above 600 whp, the Supra’s R154 or stock automatic will need upgrades (clutch packs for auto, stronger clutch and flywheel for manual). Many owners also upgrade the differential to a stronger unit.

Installation Considerations: Key Pitfalls to Avoid

Installing the Garrett G42 on a Supra is not a weekend job for a beginner. While the turbo itself may bolt to a standard T4 manifold, the rest of the system must be custom fitted. Here are common pitfalls:

  • Manifold Choice: A well-designed twin-scroll manifold is critical to realize the G42’s spool potential. Avoid cheap cast manifolds; invest in a quality stainless steel or thick-wall tubular manifold.
  • Downpipe Clearance: The G42’s turbine outlet is often a 4-bolt or V-band pattern. Check that the downpipe clears the firewall and steering shaft (on MKIV). Some fabrication may be required.
  • Oil Drain Line Routing: Ensure the drain is above the oil pan’s full level. Many Supras use a -10AN line with a low-profile fitting to avoid kinking.
  • Wastegate Placement: If using an external wastegate, route the dump tube away from the block and downpipe. A 44mm wastegate is sufficient for this power level.
  • Cold-Side Piping: A custom intercooler pipe kit is almost always needed. Use silicone couplers with bead-lock for boost retention.

Maintenance and Longevity Tips

Once your G42-powered Supra is up and running, follow these practices to keep it healthy:

  • Change oil frequently (every 3,000 miles or after each track day) using a high-quality synthetic 5W-40 or 10W-40.
  • Allow the engine to idle for 30-60 seconds before shutdown after hard driving; this lets the turbo cool and prevents oil coking in the bearing cartridge.
  • Inspect the air filter regularly. The G42’s compressor can ingest debris if the filter is damaged or not sealed well.
  • Perform boost leak tests periodically to catch any loose couplers or cracked pipes.
  • Log data (boost, AFR, knock) every time you drive hard. Catching a problem early can save the engine.

Will the Garrett G42 Work on a MKV Supra (B58)?

Yes, the Garrett G42 is also a popular upgrade for the BMW B58 engine found in the new Supra. The process is similar but requires a different manifold and a dedicated B58-specific turbo kit. Many aftermarket companies offer bolt-on kits for the B58 that include a Garrett G42 core. Power levels on the B58 are comparable, with around 650-750 whp on E85 being achievable with stock internals. For 800+ whp, the B58 will need upgraded connecting rods and pistons as well. The same reliability principles apply: good oiling, proper heat management, and professional tuning.

Conclusion

The Garrett G42 turbocharger is an outstanding choice for Toyota Supra owners who want substantial power without sacrificing streetability. Its advanced design delivers quick spool and excellent top-end flow, supporting anywhere from 600 to 900 horsepower depending on your engine build and supporting modifications. However, reaching those numbers reliably requires careful attention to every supporting system: fuel, cooling, oiling, engine internals, and tuning. By taking the time to plan each step and investing in quality parts and labor, you can build a Supra that is both exhilarating to drive and trustworthy on the road or track.

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