I have a 2007 civic si sedan which exhaust will give me the most hp?

 

Probably either an Apexi N1 or GT-Spec. That is just a guess though.

 

Youre really only going to see a couple hp either way so just get the one that you think sounds the best!

 

If your lookijng for sound and performance get a greddy Evo 2 sounds great not raspy and cheap but deep and low HP gain with just a muffler will be low i would say may 3hp+/-, But if you go the extra mile and get a header and intake then you will be able to get great sound and an easy 10-12 HP.

 

^ 3-5hp with a catback, none at all to near nothing with just a muffler.

 

look y would honda spend tons of money on research and development for some company to make something better than theres? Especially for the SI. You really arent going to get much out of an exhaust header and intake. maybe 5 hp. What ever they say you will get divide it by 2 maybe even more and you will get a more accurate reading.