I replaced mine last winter with Classic Cobra Pack. I had 2 1/2" x 24" long muffler and I replaced them with 3" x 28" Cobra Pack. The 24" mufflers had the louvers facing away from the motor. And they were loud at 4000 rpms! I installed the 28" mufflers with the louvers facing the motor. I made a lot of motor changes so I don't know what horsepower I gained because of the mufflers. I did gain about 80 hp to the rear wheels.
Now I can cruise at 70 mph and talk to my passenger in a normal tone. I have a deep rumble at idle and a Cobra tone at speed.
With the old pipes, cops could hear me 3 blocks away and I have the pictures to prove it.
I love the sound of the new pipes and I think they gain me a little hp.
The sound/tone is perfect!
Dwight