need some insight calculationing exhuast diameters

[Düb Lüv]

i need some help calculating the correct exhaust diameters for a 2-1 header. typically aftermarket headers have a 45mm(roughly 1.77 inches) diameter. my problem is calculation the correct exhaust diameter that comes off the Y. i read about calculating the surface area, but quite understand applying answer to an exhaust pipe.

[He Man]

I think you are talking abotu equivalent cross sectional area ( theres voodoo science behind flow in exhaust that i dont know jack shit about) but if math is what you need!.....

But if that is it, then add the cross sectional areas up of the 2 ins and divide by pi, and find square root to find equivalent radius for a single pipe that has the equivlent cross sectional area.

but be aware that im pretty sure thats now how it works with exhaust since the speed of the exhaust coming out is a factor in pressure and flux capcitance.

[Düb Lüv]

i used 1.75in cause it would be hard to find metric exhaust piping in the states.

header diameter 1.75inches = .875in radius


              2
area= pi r
                         2
area= 3.14 x .875
     =3.14 x .765625
     =2.4040625

2.4040625(for one pipe) x 2= 4.808125(for 2 pipes now)

4.808125 ÷ 3.14 =1.53125
1.153125 x 1.53125= 2.34472656


i think i did this right

[He Man]

no you squared the last number not find hte square root, dont forget you are working backarwds now.

so take 4.808in^2 which is the total X-area,  divide by 3.14= 1.53 take the square root of that

so you get 1.23 inches radius, so the new pipe is 2.46inch diameter. (okay i rounded up the ass so do it with a calculator and get it as accurate as u need it to be. )


Always double check your numbers because you should of seen that the radius you got was almost 3 times the size even though the area only doubled. and since area is a square function, your effectively making hte pipe 9x bigger which doenst make any sense.