Turbo 350 Transmission

Turbo 350 Transmission

The Turbo 350 transmission (formerly the Turbo Hydramatic 350 or TH350) is one of the most popular automatic transmissions of all time.  You will find it in millions of hot rods, race cars, and behind countless small block chevy’s.

The turbo 350 transmission is a lightweight and easy to install.  In stock form it is best behind a mild to moderate small block engine, but also work works great behind V6’s.  You can find the turbo 350 transmission setup for everything from mild use to extreme street use, however for higher horsepower most enthusiasts would recommend the Turbo 400 instead.

You can find the turbo 350 transmission in cars as early as 1969.  It was originally a jointly developed transmission by Buick and Chevrolet in an attempt to replace the two speed powerglide transmissions. During its early development stage it was often regarded as a three speed Powerglide due to its similarities to the original powerglide transmission.

Around 1983-1984 the turbo 350 transmission was phased out of GM cars in favor of the 700R4, but it can be found in some trucks and vans as late as 1987.  The turbo 350 transmission is not as strong as its bigger turbo 400.  However, despite this it’s still very popular and is generally capable of handling up to 400 foot pounds of torque.

The turbo 350 transmission was available in both a 4x4 and a two wheel drive varieties.  The difference is primarily in the outputs.  The gear ratio for the TH350 is first gear at 2.52:1, second gear at 1.52:1 and third gear at 1.00:1.   The TH350 has a very popular aftermarket following, with lots of modifications and parts available for it.  This is partially due to its reasonable entry price.  You can often pick up a used turbo 350 transmission for under $100 in your local classifieds.

The only real change that ever happened was that in the later years some of them came with a lock-up torque convert.  This provided an advantage on the highway of being more efficient.  By locking the torque converter it makes the transmission work at a straight 1:1 ratio and eliminates any slippage that naturally occurs by the torque converter.

Turbo 350 Transmission Identification

The TH350 is a two piece cast aluminum alloy.  One for the main transmission housing and fixed bellhousing, and a second for the tailshaft (tailshafts not installed on 4wd variety).  Through its entire manufacturing run the turbo 350 transmission did not really change very much.  However, the lockup torque converter is known to run at higher temperatures, so as a result, most people prefer to have the non-lock up variety since it’s believed that they last longer.

The bellhousing can be found with three different bolt patterns. Some cases have a Chevy engine bolt pattern, some cases have the Buick, Olds, Pontiac, and Caddy bolt pattern, and some have both. It is well worth getting the dual pattern, or unicase, Turbo 350. If you ever think you might do an engine swap, you won't have to worry about the transmission.

A Turbo 350 transmission can easily be identified by its transmission pan shape (which can be seen in the third picture above).  It is also recommended that you get the version of the transmission that you ultimately want (4x4 vs 2x4) since you will otherwise pay additional money to convert it from one type to the other.

Overall it’s a great transmission, and one that would go very well in most applications.