to get the full benefit of the HD300 tune you must use a cold air intake kit as well as a 4 or 5" straight pipe.
For insurance/security, it is in your best interest to get egr delete and head studs.
you will also see a small (i said small) increase if you replace your cold side cac tube.
the difference you look for is your peak egt after/during a WOT run. i had a 5" straight pipe and saw a drop of 130* in a quarter mile race over against a cat/dpf delete. cruising temps will be no different.
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