This is the reasoning behind having heavy internal parts. The Turbo 400 had to handle the torque of a big-block powerhouse as well as deliver a comfortable and reliable drive. To begin with, there is an incredible amount of inertia produced inside an automatic transmission. Gear vendors states that they have measured parasitic drag before and after on a Spintron and their overdrive units contribute only one additional horse power (way better than the 4L80E numbers). The parasitic drag is predominately centered in the torque converter (the factory changed the angle of the blades compared to the TH350 anticipating more torque input) so which converter you choose will have a big effect upon parasitic drag. Parasitic drag has been estimated at 20 to 40 horse power more than the TH350 (most state at least 20 average appears to be 24hp) dependant upon how much torque is input into the system. As soon as we get into a 'irresistible force being applied to an immovable object' then you are going to have more breakage problems with a TH350 than you will with a comparably built TH400. That consumes power for this reason the TH400 has more parasitic drag than the TH350.Ĭan a TH350 live behind a 383? Sure so long as we are talking about driving on the street.

It has a lot of rotating mass that has to come to dead stop and reverse it's rotational upon each shift. The TH400 is a massive tranny designed by GM to motivate all of the heavy cars in the GM stable with a lot of power (behind big blocks and High Output small blocks). The TH400 can be built to withstand about a thousand horse but at a price. If your thinking of going this route be advised that there is now available a six speed OD tranny from Allison that is supposed to be unbreakable (I said 'NEW' not the old school bus Allison, this one has a computer built into the tranny so it doesn't need an external computer). The TH400 with an OD is called a 4L80E (E stands for electronically controlled by a remote computer).

Turbo 350 transmission hp rating