Well, they are among the best performing mufflers, but there are plenty others with similar "gains".
This is from December 2002 5.0 Mustang mag, Muffler Dyno Shootout. They dyno test 15 mufflers on Rick Anderson's coupe. They didn't do a stock baseline since i don't think the car ever had stock exhaust, but they did do open exhaust with no mufflers.
Open - 365.2hp/330.1tq
Bassani Street - 372.0hp/330.1tq
Bassani Real Street - 373.7hp/333.8tq
Borla XS - 373.3hp/332.6tq
Borla XR1 - 370.0hp/334.0tq
Dynomax Ultra Flo - 369.4hp/333.2tq
Edelbrock Performer RPM - 370hp/331.3tq
Flowmaster - 369.4hp/331.8tq
Flowtech Afterburner - 372.3hp/330.1tq
Flowtech Terminator - 369.5hp/331.3tq
Flowtech Warlock - 366.3hp/325.3tq
Flowtech Warlock *opened* - 374.2hp/333.1tq
Hooker Aerochamber - 372.1hp/330.4tq
Hooker Maxflow - 373.5hp/333.0tq
MAC - 372.3hp/331.5tq
Magnaflow - 372.8hp/332.5tq
SpinTech - 371.6hp/332.2tq
So the Magnaflows fall into the upper HP/TQ range out of the ones they tested but they also fall on the lower end of the decibel reading out of all tested. I'm not gonna type out all the averages but they were among the highest average hp/tq throughout 4,700rpm-6,600rpm. The point is that unless you're shooting for some kind of peak hp record where very pony counts, you really can't go wrong with just picking what you like the sound of the best.
This is from December 2002 5.0 Mustang mag, Muffler Dyno Shootout. They dyno test 15 mufflers on Rick Anderson's coupe. They didn't do a stock baseline since i don't think the car ever had stock exhaust, but they did do open exhaust with no mufflers.
Open - 365.2hp/330.1tq
Bassani Street - 372.0hp/330.1tq
Bassani Real Street - 373.7hp/333.8tq
Borla XS - 373.3hp/332.6tq
Borla XR1 - 370.0hp/334.0tq
Dynomax Ultra Flo - 369.4hp/333.2tq
Edelbrock Performer RPM - 370hp/331.3tq
Flowmaster - 369.4hp/331.8tq
Flowtech Afterburner - 372.3hp/330.1tq
Flowtech Terminator - 369.5hp/331.3tq
Flowtech Warlock - 366.3hp/325.3tq
Flowtech Warlock *opened* - 374.2hp/333.1tq
Hooker Aerochamber - 372.1hp/330.4tq
Hooker Maxflow - 373.5hp/333.0tq
MAC - 372.3hp/331.5tq
Magnaflow - 372.8hp/332.5tq
SpinTech - 371.6hp/332.2tq
So the Magnaflows fall into the upper HP/TQ range out of the ones they tested but they also fall on the lower end of the decibel reading out of all tested. I'm not gonna type out all the averages but they were among the highest average hp/tq throughout 4,700rpm-6,600rpm. The point is that unless you're shooting for some kind of peak hp record where very pony counts, you really can't go wrong with just picking what you like the sound of the best.