I have a 2000 s4 w/ 121k, I bought the car w/120k from a pair of older college professors, all the maintenance records were given to me at time of purchase(so the car was well taken care of). My question is im debating buying a chip but am skeptical because it has the stock turbos and don't want to have the expense of having to change them soon and in the event that I do decide to do it and later decide to upgrade to ko4's can I use the same chip or do I have to replace it.

 

120,000 mi on stock turbos is good! I have 71,000 miles on the stock turbos and theyre on the way out the door.

A chip is going to let your turbos make 2x the stock boost, which will kill them faster. All of the chips are about the same with respect to what they do, but they do have slight differences. GIACx or a custom stage1/2+ tune will be most agressive, MTM is sometimes called "smoothest", APR uses the cruise control as an on/off switch so you can keep the car running stock boost when you want. There are others out there, but these are the only ones id consider. If you dont give the buisness to a tuner who is involved in innovating products for the S4, you might as well give it to the big guys who ave good reputations and support like MTM, APR, and GIAC. Thats my logic at least.

If you plan on keeping the car for a while you will probably have to replace the turbos at some point, especially if you use a chip to boost to 19psi. You cant tell exactly when the turbos will go. The best you can do is let the car (oil) warm up before you start boosting especially when its cold out, and then let the car cool down after hard driving before turning it off. If you dont do this you run the risk of cloging the oil feed lines to the turbos with congealed oil. This is a notorious reason for turbo failure especially on the passenger side because the oil line is right on the manifold. Probably contributing to my turbo failure.

Chipping the car can also expose boost leaks like diverter valves leaking, or contribute to tearing the throttle body boot. A bad boost leak if not fixed can make your turbos work harder to achieve boost and contribute to failure.

A chip is one if the most exciting mods you can do to your car. It turns a modest 250 HP sedan into something so much more. The most exciting mod is new turbos You can install K04's alone and be stage 3 minus (3-). Again several tuners can provide you with a stage 3- tune, Or you can use the GIACx chip with a couple other goodies and get the same effect. GIACx really responds much better than any of the other major chips. I would never try it with my APR chip. Running K04's on K03 tuning is not advised, the car will run much better with a stage 3- file. One dissappointing thing about stage 3- is that the K04's have the ability to completely max out the stock fueling. This link shows some logs of k04's on APR tuning. notice the injectors are working at 150% capacity

Replacing the turbos is inevitable. I would reccomend chipping the car and having a good time. You might want to get a new TBB and DV's also. APR is a good stage 2 software and will let you keep the car in stock mode sometime if you want. WHen you get k04's sell the APR ecu and get a stage 3- ecu. You will probably want to get fueling at some point. Modding is addicting.

 

You don't have to replace it.
But don't expect any gains without at least a stage 3- tune and a 5 bar fuel pressure regulator.
Use the Search and S-car FAQ sticky, there's shitloads of info on this exact question.

 

Damn, HP.. I mean, SourDiesel. You beat me to it, but you were a little more generous than I.