Tall vs Short Stacks and Headers.
The height of a Stack will dictate where your peak power/torque occur. It will not change the max hp or torque much.
The longer the Stack and /or header is, the lower the rpm that the peak power will occur at.
So if you want better high RPM power, and for it to not flatten out at a low rpm like, 5500-6000 maybe, you will want to have a 4″ or 6″ stack – then it will then lose a tiny bit of off the line torque, but will gain it back by zinging past 7000 like it wouldn’t do with tall stacks.
If you want more torque at bottom end, or off the corners or off the line, you will want 8″, 10″, or 12″ Stacks.
Same for headers: cut them down for more high rpm power, and add length for bottom end torque.
Same for Raising a Hat injector up above a tunnel ram.