And last but not least...........

[Mr 5 0]

William:

If you intend to retain the factory heads and intake and do few other modifications to your Mustang then the stock headers are not the first thing I would replace, although they are a slight bottleneck due to the crimps and dimples they contain that the factory makes to ease their installation on the assembly line.

For exhaust mods, the worst bottleneck are the catalytic converters - so replace them with an X or H pipe or buy 'High-Performance' (low restriction) cats and you'll feel the difference.

Then, should you see aftermarket heads/intake in your car's future, you can consider aftermarket headers for your 'Stang.