i know you said that you tightened down all the exhaust bolts, but if you used the header gaskets that came with the mac headers, they are copper and with copper you have to tighten them down at least 3 times after numerous hot-cold cycles. around 2000rpms is where the mustangs usually have the good ol' "HUM" thats why im leaning towards an exhaust leak. it is possible that it is a lifter or rocker arm too. hope that helps a little.
|