Let's say I have a DC JDM 4-1 Header, a 2.5" test-pipe, a modifiied B-pipe (first bottleneck removed) and stock muffler. How many HP will I gain when I switch to a full 2.5" cat-back system. Is it worth the money?

 

Are you going to go with cams in the motor later on?

 

No, no plans for cams.....

 

i'd say 4-5 over stock with a little VAFC tuning. Not much otherwise.

 

Strange thing is that many people say they gain some (noticable) HP with stock header and 2.5" cat-back. If the stock cat-back is a bottleneck for the stock header, isn't it even a bigger bottleneck for the DC header? Does this make sense?

 

there will be gains, but not astonishing ones. You'll be happy if you do the swap to the full 2.5" from SMSP! Why not save the money and get his header, cat, and exhuast. Now thats where the gains will all come together.