I am an ownere of a gs400 and my cousin just bought a S4. At first i thought that his car would be slow since it had 250hp and weighed nearly5k.

I was mad wrong. He has a biturbo which kicks ***. He had a turbo ecu installed for 300 dollars and now he is supposed to have around 320 hp. WoW

I am really impressed with the car's performance and the interior is very nice(Not as nice as in the gs )

Any one here actually raced against a s4 with the ecu. I was wondering what its 1/4 time would be.

 

S4 at 5000#......not. Listed weight is 3700#, plus he has a stick and the torque peak for the motor is 258 lb-ft at 1850 rpm. Both horsepower and torque appear to be conservatively rated based on 1/4 times. And, as you pointed out, there is a good response to modified engine ECUs.

Net result: your *** handed to you. Sounds like you got suckered if your pal told you it weighed 2.5 tons.

 

Yep S4 weighs 3593 manual and 3704 Tiptronic. Still heavy for a smaller car.
He must have gotten a used chip for the ECU. CHips run ~$595. Usually raises hp to 310-315 and torque to 330-370lbs.
For the Tiptronic it costs another ~$300-$400 for a Tip chip(transmission). But must be careful because the Tips are rated at 313lbs max torque, so with some engr fluff you can probably operate between 330-360lbs. The added stress though will shorten the life of the parts.
Stock manual S4's have run a best of 13.9 1/4 but they average between 14.1 to 14.4. The Tiptronic stock runs a best of 14.6 with the average about 14.7-14.8.
With a chip only mod times drop to a best of 13.4 manual average about 13.6-13.8 and the Tip best is 13.8 with the average about 14.0-14.1.
DO not feel bad, Your car has more room and others features that make it a very nice car. Neither car is a drag racer. 4 door family sedans , that have some fun factor. S4 much smaller inside but a nice all around car with AWD.