I've built up 3 Gm engines for performance and the consensus by everyone in the power building community is that flowmaster mufflers suck. They give a nice unique sound, but they flow awful. WORSE than stock in most cases. Consider the following. The majority of factory mufflers and the high performance free flowing mufflers for that matter all use a straight through design that cancels out noise with fiberglass wrapping around a perforated tube. Flowmaster on the other hand uses "sound chambers". This is what offers the distinct flowmaster sound, but what is essentially happening inside the flowmaster muffler is exhaust gases are bouncing from chamber to chamber in a very inefficient manner. You may notice more low rpm torque with flowmasters and that is simply because your exhaust system backpressure has increased. That increased backpressure with hurt your mid range and top end. To make power with big V8's you want as little backpressure as possible while maintaining the velocity of gases out the pipe. The best flowing high performance mufflers, aside from all out race mufflers, is the Hooker (Max)imum flow muffler and the Dynomax Ultra Flow muffler. I'm not trying to say that bolting on one of these two mufflers will give you some massive performance gain, because I'm not familiar with the hemi exhaust setup. If your stock mufflers were restricting exhaust at all stepping up to a higher flowing muffler would in fact offer a gain. The best way to build power in the exhaust is to start with a good set of headers and work your way back though. Nice ceramic coated headers dumped into a good mandrel bent Y pipe, into a high flow cat, into a nice big mandrel bent catback exhaust dumped out of some nice free flowing mufflers. That is how you make the power

You can see some flow tests here --

http://www.broaderperformance.com/mu...flow_tests.htm

 

I just had my exhaust done on my 05 Ram QC. While Flowmaster wasnt my 1st choice, my uncle who works at a muffler shop only deals with Flowmaster, and I got a Cat back system for 350 out the door. According to him, Flowmaster makes a specific Hemi muffler designed for this engine. He put dual exhaust on it after the muffler, so its not true dual. From my understanding the Hemi Flowmaster muffler is similiar to the 50 series. It does sounds pretty mean. I had him tuck the tips, which look like megahorns, at a slight angle downward in the rear corners. Not only does it sound mean, but it looks mean. I have already felt the difference at the gas pump. Granted it may not be major $$$, but a couple/few extra miles per gallon help. So far so good. If I get a chance, I will post a pic of the exhaust job...