John Telford

Hi, so to start off I want to apologize if this exact same question with the same mods has been asked before. I just bought a B5 s4 and while it isn't slow, I would like a simple ECU Tune (Flash?). My question is, based on these mods, how far can the car be pushed and what kinda tune is it ready for/can handle.
Here are the mods:
XSPower downpipes and exhaust
XSPower side mount inter coolers
XSPower charge pipes
Not sure the name of the diverter valves but they are after market too
Again I apologize if I sound like a noob I do not know too much about this platform, thanks!

Flyboy

A K03 stage 2 tune is what you'd be looking for. Generally they increase boost to about 15-18 psi on the initial boost onset and then taper down to around 12-13 psi by redline. You may pick up around 60-75whp depending on the fuel you have available.

rdcyclist

I believe those intercoolers are less efficient than stockers. The only upside to them is the welded on end tanks so they won't separate at higher boost levels. You'd do well to find some RS4's when you go to Stage 2.