mightyb28

If you swap to an S4 engine just get an S4. The issue is you have to drop the engine to do any work on it, or the turbo. Not worth it. You can do a lot more with the A4 rather then the S4. I researched the hell out of this before i got mine.

Now on lag and turbo's.

Now on 4 bangers and the air.

Yes all engines have limitations and that is where fuel comes in. F1 has has four banger twin turbo's and looks to again. Vibration is the issue with the amount of PSI you are pushing in. Fuel is easy. Adjusting the turbos to the limitations of the engine design is the issue.

Contact a company like API, or Audi tuner shops and get a professional opinion.

My feeling, and not being a certified mechanic, is that your A4 running dual K03's with upgraded fuel pump and injectors will run easily past 400 AWHP, but again you have engine vibration and the internals.

My Audi tuner shop and i sat down and talked on this as TWO SMALL TURBOS ,non sequential, will pretty much eliminate the lag and allow for bigger power gains as you now have twice the PSI to be pumped in.

This has all been really vague for the most part, but I hope it makes you understand better as it took me time to do as well since I would only install S/C before my Audi.

Do some calling around and talk to the pro's.

K04-S4

A single K03 on a 1.8T and dual K03's on the 2.7T run same stock PSI.

Dual Turbo's in parallel (non sequential) does not automatically double the PSI... just saying