After doing some searching on 3" exhaust systems, I've found it abundantly clear that there is one general consensus on header size for cars running either ported eatons or twin screws running under 625rwhp: stay with the 1 5/8" collector size with a 2.5" exit. HOWEVER, there is little to no empirical evidence (that i've found) suggesting that 1 3/4" collector sizes cause detrimental effects to the power band for the ported or lower boosted cars. It seems to me that word of mouth and the generalization "1 5/8" under 600rwhp" has relentlessly plagued this discussion. I'd like people to chime in here with technical information supporting either side of the argument, hopefully with dyno graphs and actual #'s to support their claims. It seems to me that higher boosted ported cars trapping 126+ with the proper setup (gears, pulley combination, tune etc) could benefit from running 1 3/4" primaries (1 7/8" is probably too big). Let's start this thing.