I did the cat back on my V6 and the sound is incredible. I have to say one thing though that I was disappointed in and that was in the quality of the clamps. When torquing them to the specification I could tell the nuts were about to strip. I ended up replace all the clamps with better ones.
Well, when you really get on these cars, they tend to have wheelspin, especially from a dead stop. Even with traction control... thanks to the 6-speed's low first gear.
Exhaust system design is always "give and take"... In this particular case, the larger exhaust will help more than it will hurt. I'll sacrifice a few ft-lbs in low rpm for a few more horsepower higher in the power band.
To answer your question...The carbon fiber mufflers are primarily a sound choice. You really can't see them under the stock bumper anyway, and once the Street Scene skirt goes on the back, you won't see them at all. They tend to sound somewhat like a G35 under wide open throttle, yet have a very tame sound at low rpm. I've seen them used on other V6 cars... 2005 Altima's, etc., and they perform very well.
Future plans are for possibly supercharging as well, which will move the torque back down in the power band, but I cant do anything that extreme until the warranty is up. And, ultimately you don't lose torque (unless it's a horrendous design). You just move it higher in the power band. It will likely move the torque band about 500-750 rpm higher, and add 10-12 peak ft-lbs. Since horsepower is a function of torque and rpm, you gain more horsepower by moving the torque higher in the rpm range.
Being as the exhaust from the cat forward isn't being modified, the low end torque won't really be that effected and should only move a few hundred rpm.
If you put that big of an exhaust in a 4 cyl, you'll be sacrificing drivability. The 6 cyl is a totally different story, especially when paired with the 6-speed auto.
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