i was thinking since my LS has only a single exhaust tip, that when i add a dual exhaust catback system i would gain the HP and MPG?

but in any case, i still need a new exhaust...any good brands i should stick with?
i was thinking about borla or a magnaflow, and 3.5" tips should look good right?

 

You aren't adding true dual exhaust. You are just putting a Y pipe in and splitting to 2 mufflers. You don't gain any power in these cars with a cat back, just alter sound.

I gave a 4" tip and think it fills the rear end beautifully

 

dang 4" lol, ill try that out. what brand of exhaust systems would you recommend?

 

Mine is a GM performance exhaust. But it was discontinued. However they used all magnaflow parts.

 

what do you think about SLP exhaust systems? idk if this will work for the LS...

SLP Exhaust System for Monte Carlo SS: 3800 Performance

^ ^ ^ Link ^^^