Tools & Fabrication - gonna make some headers, need some advise

I noticed some headers have a taper just behind the flange. anyone shed some insight to this?

I'm looking for an ideal tubing size for 400-600 hp range.

Here's what I'm thinking - no taper, 1.75 o.d. x .095, 4-2-1 design
its for an offroad race truck but would likely work for some street setups.
Looking for a design to pull maximum midrange torque with decent top end, but no higher than 7k.

the taper is there because the exhaust coming out of the chamber has a ton of energy and velocity, but as it leaves the head it looses energy quickly and needs a larger cross section not to restrict flow... what that is depends on the amount of power you're actually making.

Something like what you're describing isn't likely to need anything like that

the taper is there because the exhaust coming out of the chamber has a ton of energy and velocity, but as it leaves the head it looses energy quickly and needs a larger cross section not to restrict flow... what that is depends on the amount of power you're actually making.

Something like what you're describing isn't likely to need anything like that

cool im shooting for the 500hp mark to start but I would like ppl with up to 800hp to be able to use these.

Here's the layout so far
4-2-1
3/8" flange
1.75" - 2" - 3" collector,

just wondering if 3" collector is overkill, or if the 2" tubes should be slightly larger.