I have read TPI on a 400 offers a ton of torque but little horsepower. If I bought different runners, something like this:

Hi Flo Intake runners

How would they help out my horsepower curve?

 

They would help with modification. I would siamese them top and bottom along with port matching. You would need an Edelbrock manifold hogged out or Extrude honed. You would also have to fully port the plenum and probably use a 58MM throttle body.

 

Trying using the search function.

this prevents redundant topics.

"Hi-Flo" or siamesed intake runners have been covered
so many times that I cant count.

you should be able to get all the info you need.

but, ill tell you right now If I had a SB 400 the last thing I would do is put TPI on it.

HSR (Holley Stealth Ram) or Mini-ram would be logical.

do research on those 2 products. If you are stubborn and wanna keep the Tuned Port for looks or whatever reason.. then continue the search for the Intake runners

Im all for TPI .. Hence my name; but a SB 400 has high potential of putting out serious torque and horse with the right combination

there is a time and place for TPI and in my own opinion its not
on a 400 small block.