What size piping would be a good size for my stock d16z6? I was thinking about 2.5" is that too big? or 2.25 would be better?

 

Stock d16z6...no mods at all?

2.00" would be just fine if you want to open up the exhaust and keep the engine stock.
2.25" if you want to upgrade for performance wise

 

id go with 2.25, 2.5 is usually obnoxiously loud and overkill for stock motors

 

i would recommend 2.25", but trust me when i say i suggest you install a resonator after the cat/before the muffler. i had a resonator-less 2.25 custom mandrel bent exhaust on my d16z6 and the cabin noise was annoying as all hell. just a suggestion.

 

i have 2.5 pipe on my z6 with bolt ons, not horribly bad, just have to but a resonator and cat on it to keep the noise down. I got 2.5 cause i plan on swapping in a b series later, and possibly going FI with that.

 

what size is the stock piping

 

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I belive 1.75"

 

I'm running 2.5 on my ls and I hate it, I actually switched with my nephew for a day with his 2.25 and noticed a difference on the butt dyno...so I will be "downgrading" soon to 2.25-2.36"

 

2.25", 2.36" (60mm), or 2.5" for an NA D16Z6 depending on your usage needs. Anything less than 2.25" is useless and anything over 2.5" is better suited to turbocharging.