i have a 3" apexi n1 replica just sitting in my garage. i as wondering is it would help or hurt my setup. my setup is pretty simple. i have....

b20z2 with 2layers oem head gasket
blox intake mani
aem fuel rail
aem pulleys
gsr tranny
using p75 with fuel pressure at around 45psi
msd plugs (also msd sci box and coil but not going to install unless recomended)
k&m filter on cheap intake tube.

my old setup was the same but with a low compression b20b and it was a very fun car. my stock exhaust broke so i was open header for a day and it seemed way faster. elt like it made power all the way to 7000. would 3" be similar?

if it is just the 3" muffler then i dont see a problem with that...now if it was 3" piping the whole way back i would say that it is too big...i know some turbo honda's that dont even run 3" piping

ok im for sure an advocate of larger exhausts BUT on a stock block motor its going to feel really slugish. i put a full 2.5" system on my bone stock b20z including a header (just a skunk2 IM and intake at the time) and it didnt feel really good untill i put cams in.

I would say its a little overkill for an NA setup.

too big, 2.5 should work better

I think the only honda engine to benefit from a 3" exhaust is the K series... that an turbo cars...

agree

running a 3" exhaust on a honda is prolly almost like runnin open header

2.5" is enough for top end (if cams make power up top) and 2.38" for mid to low end torque. I wouldn't go anything bigger than 2.5".

Why would 3" be too big? Don't cars make more power running open header?

Wouldn't less restriction net more gains?

more horsepower, but less torque...you want some backpressure

Why is backpressure desireable? Aren't backpressure and restriction related? I can understand a drop in exhaust gas velocity would be bad, but why would reducing backpressure hurt torque?

3 '' is too big for b20 whit non vtec head

like the reply of integraguy04 say 2.5 is the best