300 exhaust
 

Hey everyone new to this site. I have a 94 300 inline six and i put the dynomax super turbo muffler on it with single in and out with 2.5 in inlets and out lets with 2 1/4 pipe. Now here is my question when i had true duals glasspacks on it i was getting 18 in the city with the a/c on, and now i'm luky to get 15 with out a/c and get around 230 miles on a full 18 gallon tank. And also when u rev it up a little and let off it has a fluttering sound is that normal?

Glasspacks are basically straight through and free flowing when compared to the design of the muffler you installed. See picture on their website. http://www.dynomax.com/mufflers.php?muffler=superturb

So I'm not entirely sure how that effected your MPG or if it has anything to do with the flutter you described. But it very well could be part of it.

It had the fluttering sound with the glasspack as well. Wasn't as noticeable