Exhaust-Mild steel vs stainless steel
 

Stainless steel is the preferred material for 'zorsts' but I've been toying with getting a system made up in mild steel. Would a mild steel system give a deeper sound? I'm thinking a sound akin to the Miltek on boost but deeper. Has anyone had experience of trying mild steel exhausts on their Impreza?

Hks use it in some of there systems..
And if I remember right they use it Japan on high hp cars.

But they do rot quite quickly in our weather conditions.
That's why stainless is a preferred metal..
And always do normally have stainless Box s on back

Mine is a mild steel one and it is defo deeper than a full steel one

Can you get butterfly valves? Would that make it sound better?

Absolutely

Yes, they are expensive though and iwll restrict the power when shut so you wont be able to drive on boost.

They wont rot if treated properly...