Hammer, I'm not disputing what you are saying, but when a person can run cats only and still not have an extremely loud truck, that tells me that the cats are restrictive. I replaced my stock cats with about 27000 miles on the clock, and went with magnaflow spun convertors. The actual convertor is round and 4 inches long with 2, two inch nipples, one on each end, 8 inches total length, and they are about as straight through as any cat could ever be, and I'd guess at least 200-300 percent more efficient than the stockers. I'm sure there are some cats advertised as High Flows that arent that much different from stock, but these are really hi flow efficient cats that are 49 state legal, and may not have been around when your testing was done. The sound increase alone was amazing to me, and my truck runs much better with these than with the stockers. Just my thoughts and opinion

 

Noise does not equal flow. At part throttle, my Mustang is louder with a pair of high flow cats than with no cats at all thru Flowmasters and Magnaflow mufflers. (I have both)
Just a note, a gutted out cat is also restrictive due to the turbulence created in the cat body.

I'm not saying that Magnaflow cats don't flow better than the ones on my 08, but not enough to validate the cost to remove good oem's for the minimal gains. Like Hammer, I would install them to replace bad stockers for sure.

 

If what you are saying about noise and flow is correct, then what is the reasoning behind replacing stock mufflers with performance brands. As I see it the restriction of the baffles in stock mufflers cancel out unwanted sound waves, but by doing so also adds restriction and less flow to the exhaust, thus less performance and less noise. When going to aftermarket mufflers there is less restrictive area inside the mufflers, therefore more flow, and also more noise. The cats should work the exact same way, so as I see it noise and flow are definately connected...IMO

 

Well Flowmasters are louder then the stock exhaust yet flow worse then the stock exhaust.

 

And you have proof to back up this statement. Flowmaster may not flow as good as a straight thru design muffler, but I'm sure that they flow better than any stock muffler

 

He may not, but I actually do have data to represent many mufflers. I put myself through college working at a pretty high end performance shop and have worked with some off/on over the years. As recently as four years ago, I worked at one almost every saturday as a second job for extra cash after my ex nailed me big time in our divorce.

There is a LOT of technology in muffles/exhaust systems today and more than baffling is used to create the desired exhaust note. Some "straight through" mufflers can actually be more restrictive than some baffled or wing plate designs because a lot of the newer baffle systems are created in a way to scavenge exhaust gases faster than just an open chamber.

When I was younger and had muscle cars, the belief was no muffler could flow as freely as a good old glasspack, but the Cherry Bomb Vortex, for example, creates a vortex within the muffler that scavenges gases through it and actually pulls these gases away from the exhaust manifold and thus outperforms even a straight though glasspack and even a straight, muffler-less system.

Dodge Ram OEM
2nd Generation: 285-355 depending on year and engine.
3rd Generation: 365-390 depending on year and engine.

Very Restrictive:
Walker PF29: 217
Thrush CVX: 260
Thrush Boss Turbo: 297
Gibson Superflow: 311
Hooker Super Competition: 320
Summit Turbo: 331
Flowtech Afterburner: 342
Summit Fully Welded: 343
Flowmaster 40: 352
Flowmaster 50: 362

Better Flow (about average for after-market):
Dynomax Super Turbo: 410
Cherry Bomb Pro: 470
Flowmaster 10: 490

Very Good Flow:
Cherry Bomb Extreme: 500
Thrush Magnum Glasspack: 507
Cherry Bomb Glasspack: 510
Edelbrock RPM: 579
Magnaflow 88: 579
Cherry Bomb Vortex: 580

Numbers given represent CFM rates. Some data was collected from various independent tests while other was obtained from the manufacturers.


As you can see, there are some very good sounding, deep, throaty mufflers that are quite restrictive while at the same time some mufflers that offer that type of sound that are very free flowing.
It's my personal belief that the difference lies with companies who choose to spend their $$$ in advertising and there are some who choose to spend it on scientific research and product development...

 

^^^ That. Hammer has a post in the FAQs where I learned that from.