[Super73]

I am told dual 2.5" will support about 2,500hp on a hotside.

I am going to be using Columbia Mandrel for my piping. Since my heads have a 1 3/4 exhaust cross section, I need to go 1 7/8 OD primaries. CM makes a 1 7/8 x 4 collector to a 2.5" but nothing smaller. This is what I will be using with their 2.5" to T4 adapter. The turbos are more or less going to sit above the control arms so there won't be a lot of tubing anyway. The collector is going to be welded directly to the adapter and mounted to the turbo.

With the 418" motor I don't think 1 7/8" and 2.5" up pipe will slow spool that much being how close to the head port they will be. Plus, I plan on spinning 7,400+ and still using a decent sized converter. In addition I have a t-brake and 2 step. I have no doubt this thing will spool plenty fast.