I have 3inch downpipes , but I am worried if oem catback is robbing to much power

 

In a situation where the power level is 700+ it may be issue. OEM muffler should not rob too much - at least nothing you can feel. Cat-less downpipes are key as the OEM cats are where the major restriction is.

 

yeah agreed... you can also do a resinator delete and put in an xpipe... that should help... but once it gets in the muffler and the flaps are open, it's pretty much restriction free.

I did a resinator delete at a muffler shop, just installed straight pipes in that part... sounds good. $150.

 

Is it much louder than stock or just kinda sorta louder?

 

It's throatier than stock. A little louder but not much. I just did straight pipes in place of resonator. 2.5" I believe.

 

I got mine done today. Its about what I expected, resonator is pretty small. I also paid $150.

 

Nice. My buddy also did exhaust cutouts right before the muffler. Sounds like a beast. I'm going to do mine as wel. Effectively making the car trimode.
Even with the flaps open the muffler still muffles a lot of the sound since some of the gases still go through both parts of the muffler. Here's a clip with his cutouts open before the muffler.