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Can you guys tell me the purpose of someone making th400 into a 2 speed transmission.
In big power applications the Powerglide has been the auto trans of choice for the last couple of decades. It has huge aftermarket support (you can build a Powerglide from all new non GM pieces) and it's a pretty efficient design as far as weight and powerflow.
A Powerglide commonly uses a 1.80 first gear ratio. 1.69 and now 1.58 ratios are available.

However as power levels have gone up, the ratios (especially 1.80) aren't as ideal. The cars need less ratio.

This is where the TH400 comes in. Stock ratio in 2nd is 1.48. A 1.57 ratio 2nd gear is common as well in the aftermarket, as is a 1.40.

If you launch it in 2nd gear it is also very efficient from a powerflow standpoint. There is much less mass moving in 2nd gear than in any other gear.

Here's one of my customers launching a TH400 in 2nd gear.
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