It is not uncommon to lose low end torque with a modification such as a free flowing exhaust. The peak torque and the resulting horsepower may increase, but in a higher rpm range. Back in the day (carbs, points and leaded gas), we calculated the shift points and the rpms through the lights (based on the gears) and tuned the engine accordingly. In other words, you may have increased power, but you have to be doing 105 to use it. Bet it sounds good at that speed!

 

Here is my take..

I now have a dual ex system I love..

Just after I bought my 06 2500 5.7 6sp hemi, I had the y pipe cut out and a ultra flow x dyno max mufler installed, two inlets, tow out lets..

The mufler sounded great, mpg improved, but I kept blowing out the packing in the muffler ( aviod any mufler that has fiberglass packing )

After three replacement's, I had a generic walker mufler 2 inlets two out lets. mpg went down, performance went down..

Calgary mufler installed two muflers called super formula Z ( only mufler shop in Calgary that sells them ) They sound like a turbo 400 mufler, verry quiet at idle, made out of steal.

The flow patern is a Z muflers are extreamly high flow, and in average driving my low end toruqe is back, and the performance is back..

If your going to replace your stock ex sytem, cut out the Y pipe, run two individual mufflers that do not have baffels or fiberglass packing, aviod dynomax, mangna flow.

Othier wise keep your ex sytem stock, cat back ex systems, or kits have one basic flaw, they keep the factery Y pipe..

Once you make one part of a factery ex sytem better flowing, the limitations of stock sytem are more noticed, stock, every thing works by keeping the back pressure = threw out the rpm range.


2 and half in are the size of my two muflers, I kept the fabed out tail pipes that run over the rear diff and in front of the bumper ( left )

My rear tail pipes are not mandrel bent, were as most cat back kits are, I was talked out of mandrel bending the rear ex pipes due to cost and the mufler guy advised that on gas engines, its not going to make a big differance, on diesel engines, mandrel bending is the only way to go..

One othier item you might find with a high flowing ex sytem is you will notice the hemi tick..

 

I've owned several magnaflows and have never "blown out the packing"...they did get a little louder though as the packing absorbed moisture.

 

Magnaflow is a better built muffler than the Dynomax, but I have never heard of any packing problems with either.

 

even if he is talking about the one resonator + one muffler = two things. where di three come from?

a catback all by itself isn't gonna gain/lose much of anything. if you like how it sounds, keep it

 

yea, I love the sound....plus I picked up about 2mpg.
The performance difference is very slight, so I guess the next mod I need is a tuner!

 

Two resonators and a muffler, 'Feej. He's an '07, went that way starting with the '06s. C'mon man, you're a 3rd Gen section mod now, get with the program...


and to the OP, yes Flowmaster's are quite restrictive, they sacrifice flow by using a chambered design to get that sound...