How to get 400 hp out of 1971 340 .30 over

How to get 400 hp out of 1971 340 .30 over

100% correct!

AJ/FormS said
Is there a reason that you want or need 400hp?

Mo-Power is better…. LOL

AJ/FormS said
I mean 325>350 is already a ton-O-fun on the street,

Ye that’s a little bit of a spirited driver.

AJ/FormS said
and with only 3.73 gears, you'll need some bottom end torque, which will go away with a bigger cam....... requiring a higher stall ....................
What you didn't mention is your convertor's stall speed, which with a 340 and 3.73s, will likely need to be over 3000.

Would this and…

AJ/FormS said
is 40 mph in First, and 67 mph in Second.
Is that what you want?

And this also be a tire size dependent issue?

How do you calculate 40mph & 67mph w/3.73 gear?
At what RPM & tire size. The OP didn’t give the tire size and you didn’t give the RPM @ which this occurs.

I feel this is important. Not that your intending to be misleading.
But without a tire size and RPM…. There is a big difference between a stock tire diameter & 28 inch tire diameter.
At what and how do you calculate converter slip?