about 8 months ago metal storm posted a link with Db levels of 10 muffs from the mufflerguy on yellowbullet.com,it was in the race sec on moparts.
here it is.
https://board.moparts.org/ubbthreads/show...rue#Post6519022
For reference, a 14 dB increase doubles the sound level, while 60 dBs represent normal conversation and 90 dBs are considered the threshold for pain.

1. Borla XS 80db at idle, 90db at 2,000 rpm, 110db at WOT.
2. Hooker Maxflow 80db at idle, 90db at 2,000 rpm, 120db at WOT.
3. Magnaflow 82db at idle, 91db at 2,000 rpm, 114db at WOT.
4. Flowmaster 82db at idle, 93db at 2,000 rpm, 115db at WOT.
5. Flowtech Warlock 83db at idle, 92db at 2,000 rpm, 112db at WOT.
6. Dynomax UltraFlo 83db at idle, 94db at 2,000 rpm, 113db at WOT.
7. Borla XR1 83db at idle, 96db at 2,000 rpm, 118db at WOT.
8. Bassani Street 83db at idle, 96db at 2,000 rpm, 120db at WOT.
9. Edelbrock RPM 84db at idle, 93db at 2,000 rpm, 118db at WOT.
10. Bassani Real Street 84db at idle, 96db at 2,000 rpm, 120db at WOT
11. FlowtechAfterburner 86db at idle, 94db at 2,000 rpm, 115db at WOT.
12. FlowtechTerminator 86db at idle, 94db at 2,000 rpm, 119db at WOT.
13. Hooker Aerochamber 87db at idle, 94db at 2,000 rpm, 114db at WOT.
14. SpinTech 87db at idle, 97db at 2,000 rpm, 116db at WOT.

15. No Muffler 91db at idle, 103db at 2,000 rpm, 120+db.

some added info.
Here's the rest of that chart. It shows dyno hp and muffler flow. You should be able to make a reasonably good decision using this info. Any muffler info that I post, is a muffler that I have personally installed for people and can verify the sound levels on.

This review was performed by Martel Brothers:

2 " Straight Pipe 283 CFM
2 1/4" Straight Pipe 365 CFM
2 1/2" Straight Pipe 521 CFM

2 1/4" Typical Bent tailpipe 268 CFM
2 1/2" Typical Bent Tailpipe 417 CFM

2 1/2" Hooker Max Flow 521 CFM
2 1/2" Ultraflow Bullet 512 CFM
3" Flowmaster 3-ch Delta 40 389 CFM
2 1/2" Borla Turbo 373 CFM
2 1/2" Flowmaster Super 40 352 CFM
2 1/2" Flowmaster (2 Chamber) 249 CFM
2 1/2" Hooker Aero Chamber 324 CFM
2 1/2" Maremount Cherry Bomb 298 CFM
2 1/2" Magnaflow (Chambered) 284 CFM
2 1/2" Dynomax Super Turbo 278 CFM
2 1/2" Gibson Superflow 267 CFM
2 1/2" Flowmaster (2 Chamber) 249 CFM
2 1/2" Flowmaster (3 Chamber) 229 CFM

3" Flowmaster "Super 40" 426 CFM
3" Magnaflow (straight) 622 CFM

3" Flowmaster 3-chamb Delta 40 365 (offset/offset #943043)
3" Flowmaster 3-chamb Delta 40 389 (offset/center #943041)
3" Flowmaster 3-chamb Delta 40 410 (center/center #943040)

-----------------------------------------------

This test was performed by 5.0 Mustang & Super Fords Magazine, December 2002, on a '90 Mustang LX coupe with 370hp and 11 second potential:

The results in HP order:
-----------------------
1.Flowtech Warlock (open) 374.2 hp / 333.1 tq
2.Bassani Real Street 373.7 hp / 333.8 tq
3.Hooker Maxflow 373.5 hp / 333.0 tq
4.Borla XS 373.3 hp / 332.6 tq
5.Magnaflow 372.8 hp / 332.5 tq
6.MAC 372.3 hp / 331.5 tq
7.Flowtech Afterburner 372.3 hp / 330.1 tq
8.Hooker Aerochamber 372.1 hp / 330.4 tq
9.Bassani 372.0 hp / 333.5 tq
10.Spintech 371.6 hp / 332.2 tq
11.Edelbrock Performer RPM 370.9 hp / 331.3 tq
12.Borla XR1 370.0 hp / 334.0 tq
13.Flowtech Terminator 369.5 hp / 331.3 tq
14.Dynomax Ultra Flo 369.4 hp / 333.2 tq
15.Flowmaster 369.4 hp / 331.8 tq
16.Flowtech Warlock 366.3 hp / 325.3 tq

17.No muffler 365.2 hp / 330.1 tq
__________________
Rob Wade
See more of my work.....
http://s268.photobucket.com/albums/jj24/mufflrguy/

I'm interested in this info as well.

I need a single 4" for mine.... and like everyone else I want it to be quiet without costing me power. I'm thinking my single 3" exhaust is costing me some - or maybe even alot since it's a magnaflow on a full exhaust system. How big of an exhaust does 700hp need to have without it costing power?

i'm running a 3 1/2" system with magna flows, over 700 hp. it's noisy, so what. i like it & so does everyone else who hears it. i agree with crizila, there isn't any muffler that is real quite & won't rob power. i tried almost all of them. seeya.

I also don't recommend the Dynomax for quiet. I have a 4" dumping into a 3-1/2" on each side and my car's FAR from quiet. 108 DB at PIR last time out and I got sent home after the third pass.

They measure from way up at the top of the grandstands, I think about 50' from the car. The limit at that track is 103 DB.

I run Magnaflo's and they are not quiet...