Purchased two Dynomax 24250 for my 2018 6.4. Scheduled to have them installed tomorrow at local shop and got wondering about their orientation. One end is slightly longer than the other, and neither was marked with a directional arrow or "Inlet" or anything of the sort. There was nothing in the box with them except a Dynomax decal. I called the 800 number on their website for tech support, and was surprised to learn that the "long" end is the inlet. I wonder how many are installed backwards and if it really affects the sound very much since it's a straight thru design. Anyway, hope to help anyone in the future that is buying this product to have it installed correctly.