phoxking

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?

Red_Army

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.

phoxking

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

Red_Army

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

hyperblu

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.

phoxking

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.

Red_Army

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.

phoxking

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.