RE: pipe resistance
Get yourself a No Leak Flange set up From Gizmo.. They are great and the cheapest I have found.
The old style flange like you have will cause you nothing but grief. If you just touch the pipe or blow over in a wreck it will move your pipe andleak water into the exhaust and make your motor run terrible. Junk it and go with a no leak is my answer. Also make sure your pipe (if water cooled) has good orings on it so it doesn't leak in to the exhaust too. It needs to seal around your header. If your header is aluminum makes sure you have plenty of coolingto the pipeso it does not distort your header and leak there too. Good luck