FWIW, I thought the Doug's and the TTIs were basically the same before today. However, when I compared pics of both together, it's pretty obvious that the Doug's is designed even more for fit, rather than performance, than the TTI. The primary tube lengths must vary from as short as 20" to closer to 40".

I know the TTI 2" ranges from about 25" to 41", but averages out to approx 32". Neither are ideal, but the Doug's looks even more compromised. I like the way both are made, but wish I could still use my old Hooker 2" Super Comps with raised-port heads; IMO they are a better design strictly from a performance perspective.