planning to buy a header with a 2.5" collector and going 2.25" piping all the way with a Spoon N1 axleback. (Motor is b18c1 gsr)

but before i purchase the header, i wanted to know would it be better for me to buy a 2.25 header because the way i see it, this is bottlenecking no?

btw the 2.5" collector is an rmf replica by kiddracing if that has anything to do with this.

or to solve all this, couldn't i just go 2.5" all the way? i just wanted to see what you guys have to say since i already googled this and only one thread popped up saying 2.25 is good for bolt ons(which i only plan to do) unless ur making more than 180whp no?

 

2.5 header to 3in exahust all day.
yes it's better all the way around.

if you really are just doing bolt ons 2.5 to 2.5 will suffice.

 

nvm i meant i'm going 2.5" collector to 2.5" piping all the way to the 2.38" axleback, i think i should be fine and just going to run about an 8" or less resonator and a high flo cat

 

yea you should be ok.
i have 2.5 with hi flow and only a muffler.

 

backpressure is necessary for your exhaust to function properly... You can taper your exhaust with adapters, but just be careful by how much. 2.5 to 2.25 is not a drastic change, however so you should be good.

 

my bad i meant to say i'm going 2.5" collector all the way with 2.5" piping to the axleback(spoon n1) that's 2.38 so that's even better than right?

plus* running short 8 or 10" resonator and high flow cat probably from magnaflow or if i can find an oem one that's not ridiculously priced.

 

backpressure is a myth hyperblu. if you can explain how a 3" system works better all the way around then a 2.25 or 2.5 then i'll believe you.
but i know its not, seem plenty of dynos to prove it.

 

take that back, doing what i said 2 posts up except the high flow. hopefully i can get a deal on a universal replacement cat.