Best exhaust diameter for my setup

[chamath]

Hi All

We are going to do the exhaust tomorrow morning, so looking for a quick answer, my car is m52, 323i, i dont have any original exhaust parts, just got the engine with its exhaust manifolds, my plan is to do a single straight pipe with a muffler in the end, no cats and resonators. What will be the best size for the single pipe? i have all standard on the engine and setup, like the intake

1. 2"
2. 2.25"
3. 2.5"

[bluptgm3]

I think the 3.2L engines run 3.5”, so 2.75”.


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[XnWarden]

Any bigger than 3" is a waste unless you are turbo'd. For your smaller stock engine, 2.5" would be about the max I would run.