Im building my B18c1 for boost, but wont go forced induction until a few months after the build. Right now the compression will be 9.0:1. As far as exhaust systems go, im debating between 2.5" or 2.25" I have a set of dc 4 to1 headers going on it also with that 2.25" outlet to the cat. I just wanted to know peoples opinions with the lowered compression and would a bigger exhaust size affect anything. The engine wont be raced on the track till turbo is put on, basically a daily driver also.

 

Compression can stay stock unless you have a specific purpose
3" exhaust is to be used. If you can only use 2.5" for now, use that.. no need for 2.25, even for NA

You're going a bit backwards on this, but you can get it cleared up.

 

well the motor will be fully built before hand with cp pistons, sleeves, and rods. Now i read on here that too big of an exhaust (2.5") would not provide enough back pressure and rob the motor of horse power.

 

yes u are right but i think on NA header config makes difference, at the moment run 2.5" and with the turbo setup a 3" is must

 

ok thanks, but i will run a 3" for turbo without a doubt

 

yes u must use a 3" with turbo, if u don't there's the risk of overheating the turbo due to the small section of exhaust.
What turbo?

 

Exhaust size isnt going to matter much, you took the compression out of the motor so its going to be slower NA, I dont think your header and exhaust choice is going to make much of a difference.

 

thanks for the advice folks. Oh and i plan on using a gt35, i used a gt2871r with my old D16 setup and i fell in love with ball bearing turbos. The lag is minimal. Last question i have is regarding fuel pumps. I going to install a new fuel tank and add a walbro 225lph pump. Im just doing a bunch of things on this build so i wont have to do it later. Would this pump seriously affect the air fuel ratio, if im using stock injectors and regulator for now until the turbo setup. I dont wanna run too rich yet.