Would like to ugprade exhaust:

Invidia Q300
Berk Tech HFC
Headers (not sure which ones)

Would like to go 70mm the whole way so I can go FI in the not too distant future.

But, I'm wondering if it makes a huge difference to swap the headers right now or just do the exhaust, maybe exhaust + HFC.

In other words, do the headers dump out into a pipe that's less than 70mm? If so, I guess that would create a bottleneck that putting a 70mm exhaust on wouldn't alleviate all that well.

That's my thinking anyhow.

 

I'm sure it's been posted elsewhere but I last measured the actual pipe (not the reinforced area around the flange or stamping lip) to be 58mm OD.

Anything over 60 isn't going to gain much on the stock header, though going bigger will set you up nicely for a larger header and cat later.

 

see https://www.s2ki.com/forums/index.php?showtopic=634406