The Buick Grand National, often called the "GN," is a true American icon. Produced from 1984 to 1987, this turbocharged V6 coupe shocked the automotive world by outperforming many V8 contemporaries of its era. The heart of its legendary status is the turbocharger itself. While the factory Garrett T3 turbo was impressive for its time, modern turbo technology offers Grand National owners the opportunity to unlock staggering power levels. Upgrading the turbocharger is the single most effective modification for increasing horsepower on the 3.8L (231 c.i.d.) V6. This article dives deep into the top Grand National turbo upgrades from two industry giants—Garrett Motion and BorgWarner—with a specific focus on the popular 60mm and 64mm compressor wheel options. We'll explore how these upgrades work, what supporting modifications are necessary, and how to choose the perfect turbo for your street or track goals.

Understanding Turbocharger Upgrades for the Grand National

To make an informed decision, you need to understand the fundamentals of turbo sizing. The compressor wheel diameter (e.g., 60mm or 64mm) is a key measurement, but it's not the whole story. Other critical factors include the turbine wheel size, the housing A/R (Area/Radius) ratio, and the turbine housing flange style. For the Grand National's 3.8L engine, a 60mm compressor wheel typically supports power levels up to around 500-600 horsepower, while a 64mm wheel can push you into the 650-800+ horsepower range, depending on the supporting fuel system and engine build. The trade-off is spool time. A larger turbo (such as a 64mm) will build boost more slowly than a smaller 60mm unit, but it will flow more air at the top end. Matching the turbo to your engine's displacement, camshaft, cylinder heads, and intended use is paramount for a satisfying driving experience.

Garrett Turbo Upgrades: The Gold Standard

Garrett Motion is the original equipment supplier for the Grand National's turbo, so it's a natural upgrade path. Modern Garrett units feature billet compressor wheels, ball-bearing center cartridges, and advanced turbine aerodynamics. Here are two standout options for GN owners.

Garrett GT3582R (60mm) – The Street-Friendly Powerhouse

The Garrett GT3582R, commonly known as the GT35R, is arguably the most popular aftermarket turbo upgrade for the Grand National. It features a 60mm billet compressor wheel paired with a 62mm turbine wheel. This combination provides excellent flow capacity—typically enough for 500 to 600 rear-wheel horsepower—with remarkably fast spool. On a moderately built 3.8L engine with a standard front-mount intercooler and upgraded fuel system, the GT35R can reach full boost by 3200–3400 RPM. This makes it a fantastic choice for a street car that also sees occasional track time. The ball-bearing center section reduces oil flow requirements and improves transient response, meaning throttle response feels crisp and immediate. Key features include:

  • Compressor: 60mm inducer, 82mm exducer (GT3582R).
  • Turbine: 62mm inducer, T04-style 5-bolt outlet or T3/T4 dual footplate.
  • Housing Options: .63 A/R or .82 A/R turbine housing. The .63 A/R spools faster, while the .82 A/R supports top-end power.
  • Average Power Output: 450–580 RWHP with proper fuel and timing.
  • Spool Characteristics: Excellent low-end torque due to the smaller turbine housing.

For a typical Grand National street build using 93-octane pump gas, a GT35R with a .63 A/R turbine housing is a nearly perfect match. Many owners pair it with 60–80 lb/hr injectors, a Walbro fuel pump, and a turbo-specific chip or standalone ECU. For further reading on Garrett’s complete range, including the GTX versions, visit the official Garrett Motion website.

Garrett GT4088R (64mm) – Maximum Power with Ball-Bearing Response

When the goal is serious power—north of 600 horsepower—the Garrett GT4088R steps in. This turbo features a 64mm billet compressor wheel and a 76mm turbine wheel with a larger ball-bearing CHRA. The 64mm inducer moves significantly more air than the GT35R, making it ideal for engine builds with larger camshafts, ported cylinder heads, and higher boost pressure (20–30+ psi). The trade-off is a slightly laggier spool: expect full boost around 3600–3800 RPM on a manual valve body or a standard lock-up torque converter. Key details:

  • Compressor: 64mm inducer, 88mm exducer (GT4088R).
  • Turbine: 76mm inducer, 5-bolt or V-band outlet.
  • Housing Options: .95 A/R T04 twin scroll or single scroll mounts. The .95 A/R works well for top-end horsepower.
  • Average Power Output: 600–750+ RWHP (depending on head flow and boost level).
  • Spool Characteristics: Later spool but stronger pull past 4000 RPM.

The GT4088R is often paired with an alcohol injection system, race fuel, or E85 to safely maximize power. It requires a more aggressive torque converter (e.g., 3200–3400 stall) to keep the engine in the powerband during street driving. For those seeking even more flow, Garrett's GTX series uses a higher flowing compressor wheel with the same frame size—the GTX4088R is a common upgrade path. Check the Garrett performance products page for full specifications.

BorgWarner Turbo Upgrades: Efficiency and Durability

BorgWarner is another leading turbo manufacturer with a strong presence in the Grand National community. Their S-series turbos (S200, S300, S400) are known for extreme efficiency, robust ball-bearing options, and impressive power-handling capabilities. Two sizes stand out for the GN.

BorgWarner S300SX (60mm) – The Modern Street Turbo

The BorgWarner S300SX line offers a 60mm compressor wheel with excellent flow characteristics. The most common variant for the Grand National is the S300SX 3.5 (60mm inducer / 80mm exducer) with a 52-53mm turbine wheel. This turbo is often compared to the Garrett GT35R, but it typically achieves slightly higher peak efficiency and a wider flow range. The extended-tip billet aluminum wheel reduces inertia for faster spool. On a mildly built 3.8L, the S300SX can reach full boost by 3300 RPM and support up to 550 wheel horsepower. Key features:

  • Compressor: 60mm inducer, 85mm exducer (S300SX 3.5).
  • Turbine: 52mm (or 53mm) inducer, 65mm exducer, often available with a T3 flange.
  • Housing Options: .70 A/R or .85 A/R turbine housing. The .70 A/R is a favorite for response.
  • Average Power Output: 450–550 RWHP.
  • Spool Characteristics: Slightly faster than a comparable Garrett GT35R due to the extended-tip wheel.

The S300SX is a direct bolt-on upgrade if you use a T3-to-T3 adapter or a specific turbine housing. It pairs well with a standard 2800–3000 stall converter. Many owners report excellent drivability and strong mid-range torque. BorgWarner offers detailed technical data on their BorgWarner Turbo Technologies page.

BorgWarner S400SX (64mm) – The King of Top-End Power

For those chasing big numbers on the dyno or at the drag strip, the BorgWarner S400SX with a 64mm compressor wheel is a dominant choice. The S400 series features a larger 6-bolt or T6 turbine flange, twin scroll options, and massive exducer sizes. The 64mm inducer wheel (often an 80mm exducer) can support over 800 horsepower when properly fueled. The S400SX 64mm is a common upgrade for race-only or high-horsepower street cars with upgraded internals. Key specifications:

  • Compressor: 64mm inducer, 80mm exducer (S400SX 2).
  • Turbine: 59mm inducer, 80mm exducer (T6 flange).
  • Housing Options: 1.00 A/R or 1.15 A/R for top-end airflow. Twin scroll housings are available for improved spool.
  • Average Power Output: 650–850+ RWHP.
  • Spool Characteristics: Late spool (3800–4200 RPM) but enormous top-end pull.

The S400SX 64mm is not a casual bolt-on; it requires a custom downpipe, wastegate routing, and often a front-mount intercooler with larger piping. It also demands a high-flow fuel system (inline pump, 120+ lb/hr injectors, and a Boost-a-Pump or dedicated fuel cell). The S400's ball-bearing option further reduces lag. For technical details and fitment guides, consult the BorgWarner aftermarket turbo page.

Choosing Between 60mm and 64mm: A Practical Guide

Selecting the right size depends on your engine build, fuel, and driving habits. Here is a breakdown to help you decide.

When to Choose a 60mm Turbo (GT35R or S300SX)

The 60mm option is ideal for a Grand National that is primarily a street car with occasional track duty. If your engine is mostly stock with mild upgrades like a chip, high-flow injectors, and a better intercooler, a 60mm turbo will provide a substantial power gain without overwhelming the fuel system or transmission. It spools quickly, maintains drivability, and is easier to tune. A 60mm turbo can run on 93-octane pump gas with a moderate boost level (around 18–22 psi) and still put down 450–500 horsepower. It also works well with a stock torque converter or a modest 2800–3000 stall converter.

When to Choose a 64mm Turbo (GT4088R or S400SX)

The 64mm option is for the power-hungry enthusiast. If you have invested in professional ported cylinder heads, a solid roller camshaft, forged pistons, and a fully built transmission, a 64mm turbo will let you push beyond 600 horsepower. However, you must accept later spool and higher inlet boost pressure (turbo lag in the context of the 3.8L V6). A 3200+ stall converter is mandatory for acceptable street performance. You will also need a comprehensive fuel system capable of supporting E85 or race fuel if you intend to run over 25 psi. The 64mm turbo is at home on the drag strip, where you can build boost off the line with a two-step or transbrake.

Essential Supporting Modifications for Turbo Upgrades

Upgrading the turbocharger is only one piece of the puzzle. To safely and effectively use the increased airflow, you must address several other systems.

Fuel System

Both 60mm and 64mm turbos require increased fuel delivery. At a minimum, swap to 60 lb/hr or 80 lb/hr injectors and a 255 lph in-tank fuel pump. For 64mm setups, step up to 120 lb/hr injectors and an external pump. An adjustable fuel pressure regulator and a hot wire kit for the fuel pump are strongly recommended. Using E85 allows higher boost without knock but requires double the injector flow.

Engine Internals

The stock Grand National bottom end (cast pistons, connecting rods) is reliable up to about 400–450 horsepower. Beyond that, forged pistons and rods become necessary. The cylinder heads also benefit from porting and larger valves to flow the air the bigger turbo provides. Camshaft selection must match the turbo’s powerband—a 212/212 or 214/214 duration roller cam works well with a 60mm turbo, while a 218/218 or 224/224 cam suits a 64mm.

Intercooling and Exhaust

A high-quality front-mount intercooler is mandatory for any turbo upgrade. The factory intercooler is simply insufficient for modern boost levels. Pair it with aluminum piping (2.5” to 3”) to reduce restriction. On the exhaust side, a larger downpipe (3” or 3.5”) and a free-flowing cat-back exhaust help the turbo spool and reduce backpressure. A quality wastegate (such as a Tial 44mm or 46mm) is necessary to control boost accurately.

Engine Management and Tuning

The stock ECU needs a reprogrammed chip or a stand-alone system like a Holley Dominator or a Fast XFI. A turbo-specific chip from a known tuner (e.g., TurboTweak, Eric Britt) will recalibrate fuel and timing curves for the new turbo’s airflow. Data logging and wideband O2 monitoring are essential to avoid detonation. A boost controller (manual or electronic) allows you to adjust boost pressure on the fly.

Installation Considerations for Grand National Turbo Upgrades

Installing a larger turbo on the Grand National requires attention to detail. The factory oil and coolant lines must be modified or replaced. Many aftermarket turbo kits come with braided stainless steel lines and -AN fittings. Ensure you have proper oil return drainage—a small pump or a properly sized drain line back to the pan is critical to prevent oil leaks. The wastegate should be mounted correctly to avoid boost creep. For T3-to-T3 upgrades, you may need a new turbine housing or a custom downpipe. If using a T4 or T6 flange (common for S400 turbos), you must upgrade the exhaust manifold or use an adapter plate. Professional installation by a Buick Grand National specialist is strongly recommended to avoid costly mistakes. Several reputable shops specialize in turbo Buicks, such as Bison Performance, Cotton’s Performance, and Savage Performance.

Conclusion: Unlock Your Grand National’s True Potential

The Buick Grand National remains a formidable platform for high-performance builds. Choosing the right turbo upgrade is the fastest way to transform your car’s character. The Garrett GT35R and BorgWarner S300SX (both 60mm) deliver thrilling street power with minimal lag, while the Garrett GT4088R and BorgWarner S400SX (both 64mm) offer massive top-end horsepower for dedicated builds. Whichever path you choose, remember that the turbo is only as effective as the supporting infrastructure—fuel, intercooling, engine internals, and tuning. By carefully planning your upgrade and sourcing components from proven manufacturers like Garrett and BorgWarner, you can turn your Grand National into a tire-shedding beast that honors its legacy. For further technical resources and build guides, explore the official product pages linked above and consult the thriving Buick Grand National community forums such as TurboBuick.com.