I got a custom designed catback exhaust installed a week ago.
i noticed that above 70mph there was a droning sound coming from the exhaust and it got really annoying on the highway.

i had to take my car back as it was just too laud .
i'm looking for a quiet ride but with performance gains.
so to make it more quieter they installed an extra resonator....
so i'm curious now , will an extra resonator decrease my hp gain and torque?

 

The resonator will not be optimal for performance, seeing as how the pipe expands then decreases in size (not uniform, hurts scavenging). I honestly don't think it will make much of a difference in output for our vehicles though.

 

well, having a catback definately helps a lot in performance

 

I'm going to play devil's advocate here for a second and disagree. The pipe has to be an ideal size for performance. Say the pipe is 3.0 inches in diameter? That would actually hurt performance in a small displacement NA motor like we have. Or if the pipe was too small, then it couldn't breathe. Am I making any sense?

 

i can tell you that i feel the difference, the car seems quicker, better throttle response, that "jerking" is gone in lower rpms and it has better passing power on the highway .
so theres definately improvement over the stock.
the catback i have is from brullen...yeah, it's true that a 3' pipe is not good for our cars...you loose lower end torque...
u see , i was told that the resonator will not effect the performance but i'm trying to see if anyone would know for sure...

 

I am not too sure of this, but of all the resonators I have seen on stock ehaust systmes (I used to work for Monro Muffler & Brake), the resonator is always larger in diameter then the pipe. I would assume that all it does, is disturbs the flow of the sound waves traveling down the pipes. As for disturbing the flow of gasses themselves, I would assume that there is some, but not large enough to be noticed.
This is a little quote from Autozone.com:
"resonator: A small auxiliary muffler, after the main muffler, used to help reduce engine noise without restricting the flow of exhaust gas."

So I guess you are OK to have a resonator! Goodluck.