so im about to buy a 2000 s4 and i want to know what the best mods are to get started. ive read that an ecu is good but what kind of hp gain will i get from that? and what else can i do to get some quick and relatively (just not super spendy) hp? how do boost controllers do on these cars and how much boost can they handle over stock without really building up the engine a whole lot? any help is greatly appreciated

There is a cute little post in the "Sticky" section that is Titled " S4 FAQ"
you will find almost everything you need to get started..
you will get some crap from other members about searching the freaking (f'n) archives (STFA)- we like to abbreviate FTW.
but i will get you started a little bit, then u can look up stuff... the ECU your speaking of is actually a CHIP which boosts HP/TQ numbers greatly as well as psi.
some manufacturers are GIAC, APR, MTM, REVO ,etc. These can go around $5-600, and will then put you in stage 1.
stage 2 will be adding a catback exhaust- whether its from BORLA, AWE, APR, Milltek etc. downpipes gets you to stage 2+ !

this is only scratching the surface to the wonderful world of modding Audi's read and learn!

Welcome to the forums... these motors are pretty strong actually... some of the best mods you can do to start are exhaust chip dv's, then worry about new turbos, k04's are a common upgrade, after that the engine is pretty safe up to 500 hp, you really cant say how much boost can be ran because it is different in all applications. As for a boost controler... dont bother, sure maybe you turned the fuel up to allow for the extra boost but then the o2's read that something is not right and the car cant correct itself therefore forcing it into limp mode... its a very complex system and its not easily tuned with a simple boost controler

(repost)

I'd would (and I did) start with the GIAC X and 710Ns. Best bang for your buck. If only the next 60hp and 90tq only cost $595.

alright well thanks. oh and someone was telling me about the other things i need to uprage when i chip my ecu and he mentioned a TBB. whats that? the bipipe?

TBB is throttle body boot. its a rubber boot that fits over the throttle body. usually cracks/ weakens and causes a boost leak.

the bi pipe is a piece that completly eliminates the TBB it fits right up to the throttle body, from what Ive heard you can get it at APR or ECS I think. It also replaces the pipes that run down the front of the engine from the TBB to the IC's (intercoolers).

TBB is the Throttle Body Boot. It can be replaced with a BiPipe or you can save a little $ and replace it alone. It's the rubber Y front and center and likes the tear under the clamps. I checked mine and noticed it was wearing through. Instead of replacing it I just turned the clamp around. ($17 saved!) But I do plan on replacing it soon. You should at least check it out. It only took me 20 minutes to get it off my first time and that was going REALLY slow.

Agh...Camo you beat me to it by like3 minutes. I defer to you because your Avatar wins.

yeah that and another good thing to get is the bently manual, and a vag com. two of the best no go fast parts i got for my car.