That's awesome. Any plans for 3" piping on an exhaust like the Magnaflow?

3" is too much for a car of this nature. unless it's FI.

sounds awesome!!!

We will have 3" available for the turbo kit builds.

sounds mean!

is that 2,5" OD tube version? to which HP you estimate this exhaust when going FI till it gets restrictive?

I mean when do one will definitely need 3" OD pipes?

with a turbocharger, yes.
with the N/A motor, no.

sorry to be nerdy, but your black'n'whiteness sounds a bit rough

having FI doesn't mean your exhaust is choking your engine, it just promts you to ask "when do I need a bigger exit door?"

I know the gas velocity physics and thermodynamic stuff around pretty well, that was the reason me asking when is the brakepoint for the tubing becoming a restrictive exit for the exhaust gases, generated by the motor?

let's say I have 2,5" tubing all around from the turbo, to the exhaust tips, so when do I start seeing choke signs and wanting to switch to 3"?

For example, AP BRZ-300 kit shows ~300whp, which is nearly doubling stock power, staying 2,5" in exhaust piping
Even more, you may stick with a stock mid-and-rear sections, which are hella restrictive being bendy and 2.1" OD

wouldn't it really relate to what kind of turbo you're dropping into the car? what goes in...must come out.

True, but it just doesn't mean that the stock exhaust is maxxed out at stock.
Don himself has said that up to 300 HP the stock exhaust was good on his setup. Adding an exhaust system to replace stock did not net any significant gains.

I'd say you NEED and exhaust for sure if you go over 300 WHP.