2004 23LSV Fresh air exhaust

[Setter23]

Hey guys im going to be building my own fresh air exhaust and cant find anywhere what size pipe they use. I have some 3" stainless sitting at the house that i was hoping i could use but if i need bigger then i will get bigger. If anybody has any insight i would greatly appreciate it! Thank you

[justgary]

My theory is that you shouldn't need more cross-sectional area than the intake throat on the throttle body, especially if it is a normally aspirated engine. 

You could argue the need for a bit more area to make up for flow loss around bends, but dumping the exhaust under water will create a lot more back pressure than the loss in the rest of the pipe. 

I probably wouldn't make it any smaller than the throttle body, at least. 

[blk93jeepzj]

Mine is the same or just slightly larger than size as the holes for the thru-hull exhaust.  Lift up the flapper and measure the ID of the pipe.  

[Setter23]

Perfect thanks for the help! Im probably going to go with 3.5 inch. It cant hurt to go bigger.

[onewake09]

I just did this on my 2017 axis. I used 3.5" mandrel bends. Only used two bends, a 180 and a 45. Material cost me like 130 shipped. Look under the diy section for my post.