Not my post but, here is where I found this post. I hope this helps you.

https://www.dakota-durango.com/threads/4-7-headers.476373/ and Post #6.

You will get two responses to this question. Some will say NO they dont make a difference and some will say YES they do make a difference.

They are both right!

Short answer is -YES, headers do make a noticeable difference on the 4.7L>>>>> but only IF you address (replace) the restrictive factory "Y" pipe with a high flow "Y". Simply adding headers to a stock exhaust system with the factory "y" pipe does not address the most restrictive point in that system and will make for disappointing gains.

Those who say NO, headers dont make a difference tend to install headers on their 4.7L without addressing the restrictive factory "Y" pipe. Sure they may have added a CAT back system which does little but change the sound and make your pockets lighter... but they are still forcing everything through the restrictive factory "Y" pipe. Very little gains will be noticed if the factory "y" pipe is left untouched.

Those who say YES headers did make a noticeable difference on their 4/7L have replaced the factory "Y" pipe with a high flow "Y" pipe and upgraded to a true 3" single exhaust.

If a customer calls me and asks what they should upgrade on their exhaust system, I ALWAYS suggest the first mod should be to replace the factory "Y"pipe with a high flow "Y" and have it merge into a true single 3" exhaust from the the "Y" back. So you would need a (2.25" dual in / 3" single out) "Y" pipe and then EVERYTHING past that point must be single in single out 3" Pipe/CAT/Muffler...

If you convert your system into a true single 3.0" system with high flow "Y"... adding headers at that point WILL add noticeable gains to the 4.7L.

If you have any questions or concerns please feel free to reach out, I can help you get the most out of your 4.7L.

And now you know the rest of the story...

SPEED SAFE, AIR RAM PERFORMANCE