I read some thread. people say cat-back exhaust system.
What is the difference between normal and cat-back exhaust
system?

 

the "cat" is short for catyltitic converter. cat-back exhaust would be from the car, back. some exhausts don't go all the way back to the cat, and some exhaust go all the way to the exhaust manifold.

 

so Cat-back is better than normal exhaust system?

 

i'd say most exhaust sytems are cat-back

 

let's try this again...
"cat back" systems replace everything from the tail end of the catalytic converter to the back of the car- pipes and muffler(s). This means all of your exhaust sensors are still in place per original spec.
A full exhaust system would typically also involve headers and everything from the engine to the rear of the car. Then there is that pesky catalytic converter- eliminate it and your emissions are out of compliance + key sensors will no longer be in place. Place it back in the middle of your otherwise new system and you have reinserted a bottleneck (albeit a necessary one) in an otherwise freer breathing system.
Cat backs are certainly easier for the backyard mechanic to deal with and offer some power gains .

 

The new Injen SES... is it catback ? Or does it replace more than that ?

 

Injen describes their dyno testing process as taking 25 minutes to remove and replace the stock exhaust with the SES.
Further, www.nopionline.com describes the system as "cat-back" which seems to confirm the installation time Injen quoted, which would be longer for a more detailed replacement, even in a well setup garage.