Originally Posted by j-rho

For me, and perhaps others, this before-and-after would be interesting, because it best represents the potential gain from where we are, to where we "could be" with the spend on the headers.

Begin: A car that already has a cat-back, cold air intake, high flow cats (or test pipes), and an optimized tune

After (1): Remove stock manifolds and tp/hfc, replace with headers. Re-tune for the headers, preferably same day/dyno/conditions (I know the installs are a PITA)

After (2): Do the above, but install a catted y-pipe, for those of us that have to retain cats for emissions or racing rules reasons (SCCA Street Touring where I run)

The reason I didn't pull the trigger on a header is I haven't seen a proper before/after done yet - one where the contribution of just the header can be observed, with all other variables properly controlled.