Th350 Vs Th400 transmission: which one to chose?

Choosing a turbocharger for your engine remains one of the critical decisions you’ll have to make. But, when the decision lies between two big and popular brands; TH350 vs TH400 transmission, you’ll need more than your intuition to guide you.

Although the production years of the Turbo Hydra-Matic (TH) 350 and TH 400 were as far as the 1960s, their durability, strength, and performance remain top-notch.

You know TH350 and TH400 hold a lot of similarities, but certain differences are worth considering. This article will cover a detailed comparison between two of this transmission, with the necessary info that will help you decide the right choice for your car.

Th350 Vs Th400 (side by side compression table)

HPHandles up to 500HPHandles up to 650 HP
Transmission3 Speed Transmission3 Speed Transmission
Manufacturing Year19691964
Body Length (Inches)21 ¾24.37
TorqueHas a low-torque transmissionHas a high-torque transmission
Vacuum ModulatorThe Vacuum modulator is in front of the right-hand side of the transmission.The vacuum Modulator is at the back of the right-hand side of the transmission
Gear RatioFirst Gear: 2.52 – 1.00
Second Gear: 1.52 – 1.00
Third Gear (Direct drive): 2.07 – 1.00
First Gear: 2.48 – 1.00
Second Gear: 1.48 – 1.00
Third Gear: 1.00 – 1.00
Reverse Gear: 2:08 – 1.00
Weight without fluid120 Pounds135 Pounds

Th350 transmission: short overview

The TH350 transmission is a 1969-released three-speed automatic shift transmission. As a joint project, Chevy and Buick developed the TH350 as the successor of the GM Powerglide automatic transmission. The duo named the transmission after themselves; Chevy-Buick Combined (CBC) transmission. 

However, the TH350 was always known for its strength, size, and ability to fit into smaller vehicles. TH350 became a household name for jeeps, trucks, and most rear-wheel-drive cars. This was not just because of its compactness, but also its adaptability and compatibility.

This transmission boasts a lighter frame. This is because the construction is solely on lighter materials. The Th350 has an aluminum alloy case and steel gears. 

Although, it has a performance level that can handle up to 500 Horsepower (HP), yet it has a low torque transmission. This is slightly lower compared to TH400 that can handle as high as 650 Hp with a high-torque transmission. 

Th350 is the right choice if you need a transmission with less weight, cost-effective price, and can fit into smaller vehicles.

Th400 transmission: short overview

Th400 transmission is a heavy-duty transmission. Released in 1964 with the model name “Turbo Hydra-Matic”, it was specifically used for Cadillac and Buick. With the rollout of different versions, they became the best choice for a transmission that can function at higher RPM and engine power. 

The three-speed automatic transmission also featured three tail shaft lengths. The built quality and design of TH400 made it strong enough to handle 4WD vehicles.

Being made from aluminum and iron construction, users have the assurance of durability and the ability to withstand heavy usage. 

However, this thick frame is exclusively designed to handle heavy-duty vehicles. While the Th350 transmission uses a reverse-cut planetary gearset, the 

Th400 transmission uses a forward-cut spiral gearset. This makes it more energy-efficient, provides better performance, and achieves efficient power transfer.

difference between th350 and th400 (5 key Differences)

1. Gearset

The gearset might not act as a noticeable difference between Th350 vs Th400, but it greatly determines the efficiency of both systems. Th350 has the reverse-cut planetary gearset, while Th400 has a forward-cut spiral gearset. 

While the planetary gearset system looks a bit more complex, it is less efficient compared to the Th400 gear set. Th400 stands as a preferred choice for high-performance cars, matching the need for an efficient power/energy transfer.

2. HorsePower and Torque

Over the years, a lot of people have misplaced the concept of horsepower and torque with each other. While both concepts explain the level of acceleration attained by a vehicle, the horsepower entails the total power output of the engine which is dependent on the torque and rpm.

Th350 boasts of handling a horsepower of up to 500hp, while Th400 can handle up to 650 Hp. There is a low-torque transmission for Th350, but a high-torque transmission for Th400. 

Th400 achieves a higher horsepower and handles more torque loads. This makes it a better option for vehicles with such needs.

3. Design

From the Vacuum modulator, the transmission’s weight, bolt patterns, and length, there are visible differences between Th350 and Th400. TH350 has its vacuum modulator located at the front of the rear position of the gearbox. 

Th400 has it placed at the right side of the same position. Th400 has a broad-looking face compared to Th350. The overall dimension makes Th400 longer, thicker, and bigger than Th350. 

Th350 lacks rigid mounted center support, with a sun shell that has a large diameter acting as the drive shell. This is contrary to the Th400 which has a sun shaft.

4. Performance and Durability

Both transmissions are great choices, but with the stronger construction of Th400, it wins the test of durability. The horsepower capacity, torque, and technical design of both transmission systems make Th400 a better option for high-performance cars.

5. Cost and Budget

Th350 is a less expensive transmission. If you want something cheaper with the needs of a low-powered car, you should go for the Th350 and not the Th400.

3 key similarities between th400 vs th350

1. 3 Speed Transmission

Both of the transmission run on a 3-speed transmission. They offer forward gear ratios (3), reverse gear ratios (1), and neutral gear. As they are older transmission models, they are still stuck with the 3-speed transmission. This is only found in old autos and not up to the same performance as a 6 speed or 10-speed transmission.

2. Input spline count

Over the years, there are certain upgrades to the materials and design of the input shafts of these transmissions. However, this doesn’t eliminate the fact that Th350 and Th400 use the same spline. From a 17 to 30 spline count, there are also the same spline converters for both transmissions.

3. Roller Clutch Design

Th400 and Th350 have similar weak spots. This starts with the roller clutch design. The weak intermediate roller clutch design impacts the weak direct clutch application of both systems.

Which one should you prefer between Th400 and Th350?

Both Th400 and Th350 have areas where they are better than each other. Understanding the comparisons between the duo will help you choose which is the preferable choice.

Now, the choice is yours! However, the Th400 is preferable if you need something for heavy-duty vehicles without considering the cost. But, if there is no need for intense or high performance, then the Hp350 is a preferable option.

people also ask (FAQs)

1. How much HP can a TH350 handle?

TH350 can handle up to 500HP. The 450 – 500Hp handled by TH350 is determined by its torque and rpm. However, you can upgrade your TH350 to handle more than 500HP. This is done with an improved clutch setup (5-clutch direct setup). You can choose between a stock clutch, stage 1 or stage 2. From the inclusion of doubled sun gear bushings to stiffer regulator springs, you can improve how much the TH350 can handle. However, you’ll need a professional repairman to help you with this.

2. How much HP can a TH400 handle?

TH400 can handle as high as 650HP. You can shoot up to 750HP without much difficulty. However, with modifications and slight calibrations, you should see our HP400 handling above 800 – 900 HP.

3. Is a TH350 good for racing?

TH350 is good for racing. With a horsepower of 450 achieved by TH350 transmission, you can pull it up for a race. TH350 has an amazing first gear and the gears are in close contact with each other. This reduces and eliminates the possibility of dropping low in power.

4. Why is it called a Turbo 350?

TH350 are called Turbo 350 because they are Turbo Hydra-Matic. The Turbo Hydramatic includes a brand and family of automatic transmissions developed by general motors (GM). 

Turbo 350 falls into the family of these automatic transmissions including Turbo 400, Turbo 180, Turbo 425, and Turbo 125. However, some drivers push the narrative that Turbo 350 is turbo because of the surge of power and HP that it releases.

If you like this post, here are some related articles you may like:

Th350 Vs 700r4: Which Transmission To Chose?

700r4 Vs. Th400 Transmission: Which One To Chose?

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