TH350

The TH350 transmission, introduced by General Motors in 1969, quickly became one of the most popular automatic transmissions of its time. Designed to replace the two-speed Powerglide and provide a lighter, more efficient alternative to the TH400, the TH350 offered an ideal balance of performance, durability, and size. Its compact, lightweight design made it a perfect fit for a wide range of GM cars and light trucks, from muscle cars to daily drivers.

The TH350 has earned a reputation for its robust construction and adaptability, making it a popular choice for everything from classic muscle cars to modern trucks and jeeps. Its 3-speed automatic design delivers smooth, reliable shifts and can be adapted to work with a variety of engines, including those from Buick, Oldsmobile, Pontiac, and GM. The use of an adapter assembly allows for seamless integration, ensuring compatibility across different vehicle models and engine types. This versatility, combined with the Turbo 350’s proven durability and performance, makes it a go-to solution for enthusiasts looking to upgrade or replace their transmission for a wide range of applications.

At Gearstar, our Level 2, 3, and 4 TH350 transmissions are tailored to support varying performance demands, ensuring that whether you’re cruising the boulevard or tearing up the track, your transmission delivers unwavering reliability.

Key Features Of The TH350 Automatic Transmission

Compact and Lightweight Design

The TH350 transmission features a smaller case size, making it easier to install in a wide range of GM vehicles without extensive modifications. Its lighter weight compared to the TH400 helps reduce parasitic power loss, allowing more of your engine’s horsepower to reach the wheels.

Three-Speed Automatic

Designed as a three-speed automatic, the TH350 delivers smooth, consistent shifts that work equally well for everyday driving and performance applications. Its well-balanced gear ratios provide strong acceleration off the line while keeping highway RPMs at a manageable level.

Durability and Strength

In stock form, the TH350 transmission can reliably handle 350–400 horsepower, making it a strong choice for many street and mild performance builds. With the right performance upgrades, it’s capable of withstanding significantly higher power levels. Its proven track record in muscle cars, hot rods, and light trucks speaks to its reliability under demanding conditions.

Versatile Compatibility

The TH350 fits a wide range of GM makes and models, including Chevrolet, Buick, Oldsmobile, and Pontiac. It works with both small block and big block engines when paired with the correct bellhousing pattern, giving builders and restorers plenty of flexibility for various projects.

Ease of Service and Upgrades

The TH350 transmission’s simple internal design makes it easy to service, rebuild, and maintain, even for high-mileage units. Its widespread use means there’s a large aftermarket network supplying performance parts, rebuild kits, and upgrade components to customize the transmission for specific power goals and driving needs.

Performance Potential

A proven favorite for drag racing, street performance, and classic restorations, the TH350 delivers both reliability and performance. When built with quality components, it’s capable of quick, consistent shifts under heavy load, making it a dependable choice for everything from weekend cruisers to competitive race cars.

Understanding the Different Levels of the TH350 Transmission

At Gearstar, we offer different performance levels of the TH350, typically Level 2, Level 3, and Level 4, to ensure your TH350 is perfectly matched to your vehicle and driving style.

Level 2 TH350

• Designed for street performance and mild racing applications.

• Handles roughly 350–400 horsepower in stock or lightly upgraded form.

• Includes upgraded clutches, bands, and shift improvements for smoother, firmer shifts.

• Ideal for muscle cars, street rods, and classic builds looking for reliable performance.

Level 3 TH350

• Built for higher-power street or moderate competition use.

• Handles approximately 450–600 horsepower.

• Features heavy-duty internal components and performance valve body upgrades.

• Perfect for big-block and high-torque small-block engines used in drag racing or aggressive street setups.

Level 4 TH350

• Engineered for maximum performance in racing or extreme builds.

• It can withstand 700+ horsepower with the right upgrades.

• Equipped with reinforced internal components, racing clutches, and custom-calibrated valve bodies.

• Ideal for full competition drag racing, high-horsepower street machines, and extreme torque applications.

Choosing the right TH350 build level ensures your transmission matches your engine output, vehicle weight, and intended use. Each Gearstar TH350 is custom-built and thoroughly tested to provide smooth, consistent shifts, durability, and peak performance, whether on the street or the track.

Frequently Asked Questions About the TH350 Transmission

How much HP will a TH350 handle?

A well-built TH350 transmission can reliably handle around 350–400 horsepower in stock form, making it ideal for many street and mild performance builds. With upgraded internal components, a custom-built TH350 from a performance transmission builder can withstand even higher horsepower levels for racing or heavy-duty applications.

Is a TH400 better than a TH350?

The TH400 is a heavy-duty transmission designed for higher horsepower and torque applications, often used in big-block and high-performance builds. However, the TH350 transmission is lighter, has lower parasitic power loss, and can be more efficient for street cars or moderate performance setups. The “better” choice depends on your vehicle’s power level, weight, and intended use.

Is a TH350 a 3 speed?

Yes. The TH350 is a 3-speed automatic transmission with three forward gears and no overdrive. It offers smooth shifts, strong performance, and a simple, durable design that has made it a favorite among muscle car enthusiasts and hot rodders.

Was the TH350 a good transmission?

Absolutely. The TH350 transmission was one of GM’s most popular automatics from the late 1960s through the early 1980s. Known for its reliability, versatility, and ease of service, it remains a sought-after choice for restorations, street performance builds, and drag racing applications.

Are the Turbo 350 and the TH350 the Same Thing?

Yes! The terms Turbo 350 and TH350 refer to the same 3-speed automatic transmission from General Motors. “Turbo 350” is the nickname that became popular among enthusiasts, while TH350 is the official GM designation.

Does the TH350 Transmission Use a Lockup Torque Converter?

No, the TH350 uses a standard torque converter without lockup. It provides smooth power transfer but allows some slippage at higher speeds.

Choose a Custom-Built TH350 Transmission From Gearstar

At Gearstar, we specialize in building TH350 transmissions that are precision-engineered for your exact vehicle and performance goals. We use only the highest-quality materials, including high-energy friction components and a high-flow filter, so your TH350 can handle the demands of high-performance driving. Each build features performance upgrades such as a TransGo shift kit and a high-performance boost valve, delivering crisp, responsive shifts and enhanced durability, and undergoes rigorous dyno testing before it leaves our shop.