Originally Posted by lilgrasshopper
Here's what came out of the article on the 4-2-1 vs 4-1:
CONCLUSION ABOUT HEADER DESIGN
So the old adage that 4-1 = more peak hp with a loss in midrange torque and 4-2-1 = more midrange torque with less peak hp is an obsolete idea.
Newer hybrid headers of the 21st century are a fusion of the old 4-1's extra length with the 4-2-1 layout, have stepped diameters, and have large diameter collectors. So you have low end peak torque with enough breathing capacity to support more peak gains (the best of both worlds).
But many of those headers are not 50-state street legal, because they do not provide a space for the stock catalytic converter to bolt up, and are certainly not legal in CA.