What if I install an exhaust header only?

[jevin]

Okay so I have a 2005 GD1 Fit (1.3L i-dsi engine) with stock exhaust and I get a squeaky noise from where the exhaust manifold meets the cat. So I'm thinking of changing the manifold to install a custom made header.

I'm doing this because I feel the manifold is getting old, but at the same time, I'm asking myself if there are any performance gains by putting in a header only. Any advice on what type of header I should get? 4-1, 4-2-1? And what about the diameter of the header? Should I keep it the same or go for thicker/thinner?

Thanks for the help.