Table of Contents
Understanding the Garrett GT55 Turbo: Specs and Applications
The Garrett GT55 is a heavy-duty turbocharger engineered for high-horsepower diesel applications, commonly found in agricultural, industrial, and marine engines as well as extreme street and competition trucks. It features a large compressor wheel and a robust turbine housing designed to deliver massive airflow—typically exceeding 120 lb/min—which supports power levels well beyond 1,000 horsepower when combined with appropriate fuel and tuning. The GT55’s ball-bearing center housing (available in some variants) reduces spool time, while its oil-cooled journal bearing version offers durability for sustained high-load use.
Before sourcing a GT55, verify your engine’s displacement and target power goals. For example, a 6.7L Cummins or a 7.3L Power Stroke can benefit from a GT55 single-turbo setup, but clearance for the oversized compressor housing and proper turbo piping must be checked. Always consult the Garrett Motion official website for the latest specifications, including A/R ratios for the turbine housing and compressor maps to ensure you select the correct trim for your diesel.
Tools and Materials: What You’ll Need for a Successful Installation
Having the right tools and parts on hand prevents mid-job delays. The following list goes beyond basics to include specialty items often overlooked.
- Garrett GT55 Turbocharger with matched turbine housing A/R
- Installation kit containing new gaskets, bolts, and crush washers
- Socket set with deep sockets (metric and SAE, as diesel engines often mix hardware)
- Wrenches (combination and flare nut for oil lines)
- Torque wrench capable of up to 60 ft-lb range (manifold and turbo clamp bolts)
- Intercooler piping (3.5”–4” diameter recommended for GT55 flow)
- Oil feed line (AN-4 or AN-6 stainless braided, depending on turbo inlet size)
- Oil drain line (AN-10 or larger, with proper gravity flow angle)
- Gaskets and seals (manifold to head, turbo to manifold, downpipe to turbo)
- Safety glasses and heavy-duty gloves
- Shop towels and brake cleaner for surface prep
- Thread-locker (medium strength) for critical bolts
- Boost reference line and wastegate actuator (if using an external wastegate)
- Creeper and jack stands for under-vehicle access
For a detailed breakdown of torque specifications for each diesel platform, refer to Diesel Power Products which provides model-specific guidance.
Preparation: Safety and Workspace Setup
Begin by disconnecting both batteries (negative terminals first) and relieving all fuel system pressure. For direct-injection diesels, the high-pressure common rail retains pressure even after shutdown—either vent via the service port or wait 30 minutes after the engine is off. Remove hood insulation if working overhead to avoid fire risk.
Drain the engine oil and coolant to a safe level if your turbo lines intersect with these systems. Many diesel engines route oil through the turbo via a top-mounted feed; pulling the dipstick or removing the oil cap can relieve crankcase pressure before disconnection.
Organize your tools in a clean area. Use a digital camera or phone to take reference photos of the original turbo routing—this saves hours when reinstalling unfamiliar pipe configurations.
Removing the Old Turbocharger
Step 1: Disconnect Exhaust and Intake Systems
- Remove the exhaust downpipe from the turbo outlet. Apply penetrating oil (e.g., PB Blaster) to rusty bolts an hour prior.
- Unclamp the intake boot (often a rubber hose with T-bolt clamps) between the air filter housing and the compressor inlet.
- Disconnect any boost reference hoses and wastegate lines.
Step 2: Remove Oil Feed and Drain Lines
- Using flare nut wrenches, loosen the oil feed line from the turbo center section and the engine block. Catch any residual oil with towels.
- Unbolt the oil drain line from the turbo and the oil pan or block drain port. The drain line often uses a flange with an O-ring—do not reuse the old seal.
- Cap all open ports immediately with clean plugs or tape to prevent debris ingress.
Step 3: Unbolt the Turbo from the Exhaust Manifold
The GT55’s predecessor, often a smaller T4 or T6 flange unit, will have three or four bolts. Loosen them gradually in a cross pattern. On some diesel platforms, you may need to remove a heat shield or transmission dipstick tube for clearance. Once free, lift the old turbo straight up—it may be heavy (up to 40 lb). Use a second set of hands to avoid dropping it on the manifold.
Installing the Garrett GT55 Turbo
Manifold Surface Preparation
Thoroughly clean the exhaust manifold mounting surface using a razor blade gasket scraper and brake cleaner. Any leftover carbon or old gasket material will cause boost leaks and uneven torque. Inspect the manifold for cracks—especially near runner 6 on inline-6 diesels. If cracks exist, have the manifold welded or replaced before proceeding.
Gasket and Mounting
- Install a new manifold-to-turbo gasket. For GT55 flanges, use a high-quality multi-layer steel (MLS) gasket that can withstand extreme heat cycling. Do not use paper gaskets.
- Apply a thin film of anti-seize to the turbo mounting bolts (typical torque: 35–45 ft-lb depending on thread size).
- Lower the GT55 onto the studs or bolts. Ensure the compressor housing orientation matches your intercooler piping—most GT55 turbos allow rotation of the compressor cover.
- Tighten bolts in a crisscross pattern to the manufacturer’s specification. If using an adapter flange, follow torque values for both flange and turbo.
Oil Line Connection
- Attach the new oil feed line. Many high-performance diesel shops recommend using a restrictor (0.060″ orifice) in the feed line for ball-bearing GT55 variants to prevent over-oiling. Journal bearing versions typically require full flow, but confirm with Garrett’s documentation.
- Route the drain line downward at a constant slope (minimum 10°) to the oil pan. Use a -10 AN or larger drain with a 5/8″ ID hose to ensure gravity flow. Connect to a port above the oil level in the pan to avoid backpressure.
- Tighten all fittings with the correct torque—avoid over-tightening that can crack the turbo’s center housing.
Intake and Exhaust Connections
- Reconnect the intake piping using new silicone couplers and T-bolt clamps. For the GT55’s 4.5”–5” compressor outlet, use a reducer if your intercooler piping is smaller.
- Attach the exhaust downpipe with a new gasket. Apply anti-seize to the v-band clamp threads if used, or tighten standard flange bolts to specification.
Intercooler and Piping Upgrades
A GT55 generates enormous boost pressure (50+ psi is common) and heat. Your existing intercooler may be a bottleneck. Consider upgrading to a large front-mount intercooler (flow capacity ≥ 1,500 CFM) with 3.5”–4” core thickness. Connect the turbo discharge to the intercooler using mandrel-bent aluminum piping to reduce restriction. Ensure all joints are sealed with silicone couplers—no boost leaks allowed. If your vehicle has a factory air-to-water intercooler, verify it can handle the heat load or replace it with an air-to-air setup.
Don’t forget the hot-side pipe from turbo to intercooler must be heat-wrapped or ceramic coated to lower intake temps. For a detailed tutorial on intercooler sizing, visit Truck Trend for performance diesel articles.
Wastegate and Boost Control Setup
The GT55 often comes as a non-wastegated unit, requiring an external wastegate (e.g., Turbosmart 60mm) to regulate boost pressure. Weld a wastegate flange onto the exhaust manifold or the turbo downpipe—position it so the dump tube does not interfere with chassis components. Connect boost reference line from the compressor outlet to the wastegate top port. For precise control, pair with a manual boost controller or an electronic solenoid (like a BoostBox).
- Set initial boost level to 35 psi for break-in, then increase to target 45–55 psi on a built engine.
- Always monitor boost pressure with a gauge during the first full-throttle runs.
Final Steps and Testing
- Reconnect the battery and prime the oil system. Crank the engine with the fuel supply shut off for 10 seconds (or remove the fuel pump relay) until oil pressure registers on the gauge. This prevents a dry start that could damage the turbo bearings.
- Start the engine and let it idle. Immediately check for oil leaks around every fitting. Slowly raise RPM to 1,500 and hold for 30 seconds to circulate oil through the turbo.
- Inspect coolant lines (if water-cooled GT55 variant) for leaks. Listen for unusual whining or scraping noises.
- Once the engine reaches operating temperature, perform a short test drive at low boost (under 10 psi). Gradually increase load while monitoring boost gauge and pyrometer (EGT). Keep EGT below 1,200°F during break-in.
Troubleshooting Common Installation Issues
| Issue | Likely Cause | Solution |
|---|---|---|
| Oil leaking from turbo seals | Drain line too small or restrictive; wrong restrictor for ball-bearing turbo | Increase drain tube ID to -10 or -12; remove restrictor for journal bearing. |
| Boost not reaching target | Wastegate stuck open; boost leak in piping | Pressure test intercooler system to 30 psi. Listen for hissing and repair couplers. |
| Loud whistle at idle | Compressor surge due to mismatched A/R; inlet restriction | Check compressor map. Ensure air filter flows >1,000 CFM. |
| Exhaust smoke (black) under acceleration | Over-fueling without enough air; fuel tuning needed | Retune ECU or adjust fuel screw; consider larger injectors. |
For persistent issues, join a community forum like Cummins Forum where experienced diesel mechanics share GT55-specific advice.
Performance Tuning After Installation
Once the turbo is installed mechanically, you must recalibrate your engine’s electronic control unit (ECU) or fuel injection pump. A GT55’s airflow exceeds factory sensors’ range—expect MAP sensor voltage saturation above 35 psi. Upgrade to a 5-bar or 6-bar MAP sensor and have a custom tune written. On mechanical injection diesels (e.g., 12-valve Cummins), adjust the AFC (aneroid fuel control) to match increased boost. Consult Industrial Injection for hardware upgrade kits.
Always dyno-tune your diesel after a major turbo swap. The gains from a proper tune can be 30–50 horsepower more than a simple “seat-of-pants” calibration.
Conclusion: Mastering the DIY GT55 Installation
Installing a Garrett GT55 turbo on your diesel engine is a significant upgrade that rewards careful preparation and attention to detail. By following the expanded steps above—correct oil routing, proper gaskets, wastegate setup, and thorough testing—you can achieve reliable, high-horsepower performance. Remember that a turbo this large demands supporting modifications: upgraded fuel system, intercooler, and driveline components. Work methodically, prioritize safety, and don’t hesitate to seek professional help for complex wiring or welding. With persistence, your diesel will roar to life with the immense power the GT55 delivers.