Introduction: The 3B Turbo Upgrade with Garrett GT35R

Upgrading the turbocharger on your 3B engine is one of the most effective ways to unlock serious horsepower. While the stock turbo is adequate for daily driving, a properly executed upgrade to a Garrett GT35R can push your 3B from a modest output to a solid 350 wheel horsepower (WHP) — a transformation that requires careful planning, component selection, and precise installation. This guide covers the complete process: from gathering the right parts and removing the stock unit to fitting the GT35R, upgrading supporting systems, and tuning for reliable power. Whether you’re a seasoned DIY builder or an enthusiast looking to understand what goes into a 350 WHP build, this article provides the technical detail you need.

Understanding the 3B Engine and the GT35R Turbocharger

The 3B engine (found in various Toyota models and industrial applications) is known for its robust bottom end and potential for forced induction upgrades. The Garrett GT35R is a ball-bearing turbo with a 61mm compressor wheel and a 56mm turbine wheel, designed for high flow and fast spool. When paired correctly with the 3B, it can deliver strong mid-range torque and top-end power well beyond 350 WHP with proper supporting modifications.

Before diving into the install, ensure your 3B engine is in good health — no excessive blow-by, proper compression, and adequate oil pressure. The GT35R requires both oil feed and coolant lines, so plan your routing early. For more details on the GT35R specifications, refer to the official Garrett GT35R product page.

Tools, Materials, and Parts Checklist

Before starting, gather the following items. Missing a critical part mid-installation can lead to delays or mistakes.

Turbo and Installation Kit

  • Garrett GT35R turbocharger (appropriate A/R housing for your application – commonly .63 or .82)
  • Turbocharger installation kit (includes gaskets, oil feed/drain line fittings, coolant lines, and hardware)
  • Exhaust manifold suitable for GT35R T3/T4 flange (if your stock manifold is not compatible)
  • Exhaust downpipe with V-band or T3 flange matching the turbo outlet
  • Intake piping kit (3″ or larger with appropriate couplings and clamps)
  • Intercooler piping kit (3″ recommended for 350+ WHP)
  • Wastegate and boost controller (optional but recommended for precise boost regulation)

General Tools

  • Socket set (metric, 10mm-19mm), wrenches, ratchets, extensions
  • Torque wrench (ft-lb and in-lb scales)
  • Pry bar and pliers
  • Coolant drain pan and oil drain pan
  • Jack and jack stands (or lift)
  • Penetrating oil (for stubborn bolts)
  • Clean rags and brake cleaner

Supporting Parts for 350 WHP Target

  • High-flow intercooler (bar-and-plate recommended)
  • High-flow fuel pump (e.g., Walbro 255 LPH or larger)
  • Larger fuel injectors (need to support approximately 550-600 cc/min at 350 WHP)
  • Engine management system (standalone ECU or fuel/timing piggyback)
  • Boost gauge and wideband air/fuel ratio gauge

Preparation and Safety

Disconnect Battery and Drain Fluids

Start by disconnecting the negative battery terminal to prevent accidental shorts or electrical damage. Drain the engine coolant into a clean container (it can be reused if not contaminated) and drain the engine oil. Remove any engine covers, intake ducting, and components blocking access to the turbocharger area.

Clear the Work Area

Remove the radiator fan shroud and possibly the radiator itself if you need extra room. On many 3B setups, the stock turbo sits close to the exhaust manifold; freeing up space makes removal and installation easier. Label and bag any bolts, brackets, or small parts as you remove them.

Removing the Stock Turbocharger

Step 1: Exhaust Downpipe

Loosen the bolts connecting the exhaust downpipe to the stock turbo’s exhaust outlet. Support the downpipe and separate it from the turbo. You may need to also unbolt the downpipe from the exhaust system further downstream.

Step 2: Intake and Charge Piping

Disconnect the intake pipe from the turbo compressor inlet. Remove the intercooler piping if it connects directly to the compressor outlet. Carefully unclip or unbolt any brackets holding these pipes.

Step 3: Oil and Coolant Lines

The stock turbo has a banjo or compression oil feed line and a drain line. Place a small tray underneath to catch any residual oil. Disconnect the coolant lines (often two small hoses) and plug them temporarily to prevent coolant spillage.

Step 4: Unbolt Turbo from Manifold

Using the appropriate socket, remove the two to four bolts that secure the turbo to the exhaust manifold (depending on your specific 3B manifold design). With the bolts removed, carefully lift the turbo out of the engine bay. Note the orientation of the oil drain gasket and any heat shields.

Installing the Garrett GT35R Turbocharger

Prepare the Mounting Surface

Clean the exhaust manifold flange thoroughly with a wire brush and brake cleaner. Use a new gasket if you’re reusing the stock manifold (or if you’re installing an aftermarket manifold, follow its gasket instructions). Ensure the studs or threads are free of debris.

Mount the GT35R

Place the GT35R onto the manifold flange. You may need to install a T3/T4 adapter plate if the stock manifold uses a different bolt pattern. Bolt the turbo in place using the manufacturer’s recommended torque specification (typically around 30 ft-lb for M8 bolts). Torque in a crisscross pattern to ensure even clamping.

Connect Oil and Coolant Lines

The GT35R uses a -4AN or -6AN oil feed (restrictor recommended if fed directly from the engine block) and a -10AN drain. Attach the oil feed line to the top of the turbo center housing; the coolant ports are typically on the opposite side. Ensure all connections are tight but be careful not to overtighten banjo fittings. Refer to the Garrett installation guide for specific line routing.

Install Intake and Exhaust Piping

Attach the intake piping (with air filter) to the compressor inlet. Connect the intercooler piping from the compressor outlet to the intercooler. For the exhaust side, install the new downpipe onto the GT35R turbine outlet (V-band or T3 flange). Tighten all clamps and bolts. Heatshielding the intake piping near the turbine housing is recommended.

Upgrading Supporting Components for 350 WHP

At 350 WHP, the stock fuel system and intercooler will be severely lacking. Commit to these upgrades to protect your engine and realize the turbo’s potential.

Intercooler

A larger bar-and-plate intercooler with at least 3″ inlet/outlet is mandatory. Mount it in the front grill area for maximum airflow. Use 2.5” or 3” piping with silicone couplers and T-bolt clamps to prevent boost leaks.

Fuel System

Install a high-flow fuel pump (Walbro 255 LPH or higher) and replace the injectors with 550-650 cc/min units. A return-style fuel pressure regulator may be required if your original system is returnless. Tuning the fuel map is critical; lean conditions at high boost can destroy pistons.

Exhaust System

A 3” turbo-back exhaust (mandrel bent) reduces backpressure and allows the GT35R to spool faster and make more power. Include a high-flow catalytic converter if emissions compliance is needed, or use a straight pipe for maximum flow.

Engine Management and Boost Control

Your stock ECU cannot handle the fuel and timing requirements of 350 WHP. Options include a standalone ECU like Haltech, Link, or EMS, or a piggyback system with tuning capability. You’ll also need a boost controller (manual or electronic) and a wastegate. For comparison of tuning strategies, see EngineLabs’ guide to tuning forced induction engines.

Tuning the Engine for Reliable 350 WHP

Base Map and Initial Start

After everything is connected and fluids are refilled (fresh oil and coolant), prime the oil system by cranking the engine with the fuel pump relay disabled until oil pressure registers on the gauge. Then start the engine and check for leaks. Let it idle and stabilize coolant temperature.

Fuel and Ignition Tuning

Using your engine management software, set a safe base fuel map with conservative ignition timing. Gradually increase load while monitoring a wideband O2 sensor. For 350 WHP, aim for lambda around 0.78-0.80 at full boost. Retard timing in the high-boost areas to avoid detonation. A professional dyno tune is strongly recommended.

Boost Level and Safety Limits

Start with low boost (around 5-7 psi) and slowly increase to achieve 350 WHP. The GT35R can deliver this at approximately 15-18 psi on a well-built 3B, depending on the A/R housing. Install a pressure safety switch that cuts ignition or fuel if boost exceeds your target plus 2 psi. For more information on tuning for safe power, refer to HP Academy’s turbo tuning guide.

Final Checks, Testing, and Break-In

Leak Check and Torque Verification

With the engine running, listen for intake and exhaust leaks. Spray soapy water on all connections (intake, intercooler, oil lines) while idling to spot bubbles. Once warm, shut down and re-torque the turbo mounting bolts, downpipe bolts, and any brackets that may have loosened from thermal cycling.

Reinstall Removed Components

Replace any engine covers, heat shields, and the radiator fan shroud. Ensure nothing contacts the hot turbo housing or intake piping.

Road Test and Data Logging

Take the car on a gentle drive to check for drivability issues. Gradually increase boost while logging air/fuel ratio, boost pressure, exhaust gas temperature, and intake air temp. If any parameter exceeds safe limits (e.g., knock, lean spike, EGT over 900°C), back off and revise the tune.

Final Word on Reliability

350 WHP from a 3B with a Garrett GT35R is achievable and rewarding, but it demands attention to detail and quality parts. Do not skip supporting mods or tuning. With proper installation and calibration, your GT35R upgrade will provide years of strong performance.

For additional resources on turbo selection and installation, visit Garrett’s turbo selection tool and for community builds, check out SupraForums discussion threads (ensure you verify reliability of forum advice).