heres an excerpt I copied off another site, with a test of several mufflers, their sound DB ratings, and HP/Torque ratings.....

"I think, lots of us want mufflers that deliver good performance and have an aurally pleasing, performance sound... without being cop-bait or causing migraine headaches on a long drive.

The best muffler comparison I've seen to shed light on available choices based on that criteria was in the December 2002 5.0 Mustang and Super Fords magazine. 15 pairs of performance mufflers were tested on a highly-tuned, naturally-aspirated, EFI 306 Mustang making about 370 RWHP. Peak power is in the mid-6000 range, peak torque mid-5000 range. Tests were run back-to-back in a single day on Rick Anderson's dyno (Anderson Ford Motorsports). Horsepower, torque, and various sound levels were recorded in the most consistent manner possible for valid comparison. Four pulls were made with each pair of mufflers, and an average used for the reported numbers. Sound was measured with a decibel meter at idle, at 2000 rpm light-load cruise, and then at wide-open throttle maximum.

None of the mufflers produced hugely-different power results, ranging from 366.3 RWHP to 374.2 RWHP, and 330.1 lb./ft to 334.0 lb./ft. torque.

There were, however, a lot of differences in sound levels produced...both in quantity and subjective quality. Sometimes the loud mufflers produced more power, and sometimes they didn't. I've listed the mufflers below and the suggested retail price EACH as given in the magazine (rounded to even dollars). In the brackets with the price, I've indicated their construction: SS for stainless steel, AS for aluminized steel, and MS for mild steel. Next is the measured sound-level results in decibels, followed by power numbers (to compare relative efficiency). Re: the decibel numbers...the first number after the muffler name is decibels at IDLE, the second number is 2000 rpm CRUISE decibels, and the third number is WOT decibels. RWHP & RW torque are listed last. (Note: OMS means "off the sound meter's scale... too loud to measure):
NO muffler ($free!): 91/103/OMS/365.2 RWHP/330.1 RWT
Bassani QT ($186 SS): 83/96/120/372.0 RWHP/333.5 RWT
Bassani Real Street ($186 SS): 84/96/OMS/373.7 RWHP/333.8 RWT
Borla XS ($130 SS): 80/90/110/373.3 RWHP/332.6 RWT
Borla XR1 ($168 SS): 83/96/118/370 RWHP/334.0 RWT
Dynomax Ultra Flo ($80 AS): 83/94/113/369.4 RWHP/333.2 RWT
Edelbrock RPM ($179 SS): 84/94/118/370.9 RWHP/331.3 RWT
Flowmaster 50 series SUV type ($135 MS): 82/93/115/369.4 RWHP/331.8 RWT
Flowtech Afterburner ($43 AS): 86/94/115/372.3 RWHP/330.1 RWT
Flowtech Terminator ($59 AS): 86/94/119/369.5 RWHP/331.3 RWT
Flowtech Warlock ($75 MS): 83/92/112/366.3 RWHP/325.3 RWT
Hooker Aerochamber ($69 AS): 87/94/114/372.1 RWHP/330.4 RWT
Hooker MAXflow ($69 AS&SS): 80/90/120/373.5 RWHP/333.0 RWT
MAC Flowpath ($80 SS): 87/98/119/372.3 RWHP/331.5 RWT
Magnaflow ($84 SS): 82/91/114/372.8 RWHP/332.5 RWT
SpinTech ($80 AS): 87/97/116/371.6 RWHP/332.2 RWT
Rick Anderson wisely points out in the article that (as always) you shouldn't look only at peak HP/torque figures but rather at AVERAGE power production figures within the engine's powerband. Best in that regard was the (very loud) Bassani Real Street, followed by a virtual four-way tie between the Magnaflow, both Borlas, and the Hooker MAXflow.

FWIW in scientific procedure commentary: Because the open-pipe version was lowest in power, my opinion is that the car was well-tuned for mufflers and the injectors went slightly lean at max rpm when the exhaust was opened up. That would suggest that a couple of the most open, high-flowing mufflers MIGHT have made a few more ponies on top with the A/F optimized for them. They're all so close, though, that this is nit-picking.

It's worth noting that there's a significant weight difference among these mufflers, ranging from 6 lb. for the DynoMax to 16 lb. for the long, 3 chamber Flowmaster. That's up to 20 lb. weight difference for 2 mufflers!

The "quality" of the exhaust note produced is impossibly subjective to quantitatively express...yet every gear head can listen to different exhaust combos and...more often than not... agree on which ones sound "good" to the performance enthusiast's ear. 5.0 magazine picked the Magnaflow, Bassani QT, and Edelbrock RPM as having the "sweetest" performance notes. FWIW, this agrees with my own casual observations.
If you want the quietest muffler you can get without suffering a performance penalty, the Borla XS wins hands-down. The ability to make power while generating only 110 db at WOT is amazing. It's 90 db cruise is also the quietest, as is its 80 db idle. Bonus is it's one of the lightest at 7.5 lb. T'aint cheap at $130 each, but the stainless Borla offers undisputed high quality with a nearly-forever warranty. Their sound reminds me of the stock, "factory muscle car" sound of the 60's. Conservative but classy.

The Magnaflow offers great value, high quality, high performance, and sweet music without the mind-numbing drone or obnoxious bellow. Only $84 each gets you shrink-wrapped, flawless stainless steel that is polished so beautifully that it will make you sad to hide them under your car. At 10.5 lb. they're still on the lighter end of the spectrum. They're only 1 db louder than the Borla XS at cruise speed, and only 2 db thumpier at idle. They open up "just enough" at WOT (IMHO) to sing a well-controlled but exuberant horsepower sonata. Fortissimo passion without pain. Even though 4 db. louder than the Borla at WOT, they're still on the low db side compared to the others in the test. I've never heard anyone complain about the "quality" of the sound from Magnaflows, and only a couple complaints about "not loud enough," (mostly from 2-chamber Flowmaster aficionados, lol).

Either of these choices SHOULD be run with an H or X pipe crossover. This will provide both better performance and optimum sound control. Either COULD be run with cats which would subdue their mildly-sonorous personalities even further."

While I think the retail prices for several mufflers are on the high side, the rest looks pretty close...
Especially note the comparison between the Dynomax Ultra Flows and the 50 series Flowmaster...one DB sound difference, same HP, and 2 ft lbs of torque...

Rule of Thumb:
--->Do not dismiss something you have not personally run.<---

Many of the fastest cars out there run Flowmaster. Yes, I've talked to people who have experienced better luck with other brands in certain cases and applications, and I'm by no means pushing Flowmaster over any other brand. I have Flowmaster 40 series 2 chambers on my 72, with a 12:1 CR 470 stroker motor, and they are house rattling, loud mufflers, which produce alot of resonance at road speed, but they work great at the track, and have little effect on ET vs. dropping the exhaust. My 70 Vista with a 350 runs stock manifolds, full duals, and shorty glasspacks, has a rumble at idle, but is fairly quiet at road speed. My 74 442 with a 455 headed 400 has full duals with headers and shorty glasspacks, with more miles on the mufflers, and they rap out like it has a SBC in it...I know people who have excellent luck with the Ravins, Flowtechs, Magnaflows, and FloPro mufflers as well. Its more of a personal choice than anything, but to say Flowmaster doesn't flow better than a stock muffler is like saying a Cutlass is just a Monte Carlo with badges... The Ultra Flows have a fiberglass dampening, which eventually will do the same thing as a glasspack...burn out and get louder...don't get me wrong..they are a good muffler too, but if you're going to put up facts, make sure they're truthful, and not based solely on personal opinion....

This one looks good for the price,but I'd like to stand next to it & hear for myself....Hooker MAXflow ($69 AS&SS): 80/90/120/373.5 RWHP/333.0 RWT

Thanks for all the info! This is great! I was about to ask what mufflers I should buy for my new 400 hp engine. Now I know.

Tumarr said: Thanks for all the info! This is great! I was about to ask what mufflers I should buy for my new 400 hp engine. Now I know.

Which ones ya gettin'?

the magnaflows look good to me. I also like the stainless steel idea since they drop salt on the roads here in chicago. Also I dont need to be a cop magnet since I am 21 one and look suspicious already.

|UPDATED|1/31/2004 9:44:33 PM (AZT)|/UPDATED|

Yah,when I had my bright"give me a ticket" yellow '77,it was an eye catcher..now I'm in a darker red '79.

|UPDATED|1/31/2004 10:01:19 PM (AZT)|/UPDATED|

I've got the Hooker MAXflow ($69 AS&SS): 80/90/120/373.5 RWHP/333.0 RWT

The sound is great. So far no complaints!

Hooker and Flowtech both have the muffler sounds recorded and can be listened to on their websites.

well,I just went & spent around $600 having all my stuff put on.I got the FM 40's,but they just came out with Super 40's that supposedly flow better yet,so I may change later.

I've had the Magnaflow for about a year. They sound awesome. They are louder at lower RPM and relatively quite at highway cruise. When you punch it, awesome sound, waaaaaaaaaaa waaaaaaaaaa, gotta love the sound of secondaries. Stainless steel straight through design. As with any muffler it is personal preference on sound. Best advise is to listen to someone else's to see what you like. I will post a sound clip if I could ever figure out how to make it and post it.