THM250 - THM350 - THM400

These transmissions are all very similar to each other externally and in function. They very in strength quite a bit though.
THM stands for “turbo hydra-matic”. People commonly refer to these as “turbo 350” or “turbo 400” for the 350 and 400 models.

The THM350 and THM400 are ubiquitous with drag racing. These are generally considered to be very strong transmissions. For most use cases they don't need to be modified to be able to withstand high amounts of power.

Adapting a 3800 to any of these transmissions requires an adapter plate and a pilot conversion hub. Here is one example of a kit with both of these parts made specifically for this conversion https://www.speedwaymotors.com/Chevy-4-and-V6-to-TH350-Adapter-Plates,3280.html

You may also need to have your flywheel drilled to accommodate the bolt locations for the torque converter for any of these transmissions.