I'm looking to get a new downpipe for my currently standard sti6 and have 2 options. One being a bellmouth the other being a twin pipe where there is a second pipe that exits oposite the turbo vanes and then joins the downpipe further down the downpipe.

Is there any technical information about which of thiese are best for producing max hp/torque and at what revs?

Also does anyone know wnywhere that will sel me a stainless flange and bellmouth section of the exhaust on;y, I'd like a go at making my own downpipe.

Cheers all in advance