Those Dynomax Super Turbo mufflers are restrictive as he11!!!! You need to either run it uncorked or, at the very least, get some good straight through style mufflers for it! It wouldn't surprise me a bit of you dropped 3 tenths by getting rid of those super turbos.

Hemis hate mufflers...they need to breathe. Definitely more sensitive to this than a wedge motor from the testing I've done. All the "old school" hemi guys told me that when I was building my hemi 12 years ago.

My dad's '69 road runner street car w/ a 480 or so hp 440-6 in it was noticeably slower when I swapped the 3" Ultra Flows for some 3" Super Turbos. He wanted it quieter, but even he was really disappointed in the noticeable loss of power after his first test drive. I knew it as soon as I pulled out on the highway leaving the exhaust shop.

My hemi runs the best either open header or w/ a pair of 4" bullets mounted right off the back of the collector (same w/ either). Everything else I've tried has slowed it down a tenth or more.