This is a collection of the information that I picked up during my first few months of S4 ownership and obsessive forum/internet searching and may serve as a guide for choosing what mods to make right off the bat, what is really worth it and what isn’t, as well as providing some basic budgeting information so that you don’t get yourself in TOO deep. All prices are for parts only, and do NOT include the cost of labor.
First of all, if you own this car, you’re already in deep.
Got a great deal on it, you say? 
TOO BAD. 
You didn’t get a better deal on it than I did (I got it for free) 
, and it has still cost me nearly $10,000 in repairs and upgrades within a few months. 
Mine was also an example of pretty much everything that can go wrong, though. 
It is an expensive car to maintain, and it is highly recommended that you work on the car yourself as often as possible.
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What you should probably do:
This is a SUPER basic quick summary. If you are unable to read the rest of this post, this section will be a good start.
First thing is to find everything that's broken. After you've spent your entire mod budget on fixing the car that you just purchased or otherwise acquired, you can move on to mods
If you have $6,000 or so laying around, just go stage 3 with K04s (~420whp). If you have $8,000ish laying around, go RS6s, Tial 605s, GT2554s, or GT2560s (~500whp), if you have a LOT more than that (I mean like $15K++ for the parts and building your motor), man up and get some big GTs or Tials: GT2560s, GT2860s, GT2871s, GT????, Tial 770s) (~OMFG whp). The 770s are probably the best choice of all of them, because they spool great and have dynod well over 600whp with proper setup. But aside from that...You could be a baller and go single turbo, but its basically entirely custom and gets expensive. It's been done and it can make probably more power than any twin setup. PM for help figuring what parts you'll need for Stage 3 power levels.
Right off the bat:
Note: No one is really going to be able to prove what the best, most important first mod is. A chip, suspension, or a shifter are the three best first choices, IMO.
This is simply my opinion, but the first thing that you should do is get a JHM "solid" short throw shifter. There are other shifters that are decent (toy guy, B&M) but this is Big League Chew. Shifting the stock shifter reminds me of attempting to shift a flacid genital. Since you spend so much time with your hand on said device, you just don't want to be thinking about how it feels like a floppy wet hog. It just makes it feel more like a sports car, is a fairly easy entrance into the DIY work on this car, and isn't very expensive.
One can argue that a chip will be the most bang for buck right off the bat, and result in the most "increased" fun, and they're probably right. GIAC and APR are the most common chips, and neither one of them is noticeably better than the other for it to matter which one you get.
So, get a chip in there, put a silicon throttle body boot in (because your stock one will tear soon) or an APR or ARD bi-pipe, and replace the f-hose if you have one (2000s and some 2001s have them).
Before you even do a catback, you should put a boost gauge in so you can make sure you're boosting to safe levels. Plus you can now enjoy watching the analog representation of the sweet new power that you're making.
Next, catback + piggies. The sound alone will make you happy. Doing a catback and piggies will net you another 30+ bhp or so.
Thrown in there randomly, or after you finish, it's time to consider things like your Diverter Valves (DVs) and your clutch/flywheel. I did my DVs before I did anything else. Throw in a DarIntake mod because its free (same with Piggies if you're a real man). You can also do Water/Meth injection for some more power/advanced timing. You will probably also kill your fuel pump, so start planning to replace it with a high performance one. DeatschWerks 300LPH is good (vast sells it), Bosch 044 (270lph) is better, but probably more than you need, and you can also do an inline fuel pump for cheaper.
If your roads are good, you can lower the car with H&R springs (can get very low) or vogtland lowering springs. If you want to be economical with suspension, do Bilstein sport shocks and some springs. H&R for very low, vogtland for more manageable. Koni Yellow shocks are good too, and are adjustable. If you want to get real handling performance, get a coilover setup (H&R, Stasis, Vogtland, KW, or Bilstein). It was one of my my favorite mods. If you want to spend the least amount possible, but want increased handling, a rear sway bar will make a noticeable difference, and even let you oversteer.
Tranny and motor mounts make a big difference, as well as a snub mount.
Oh, and you almost definitely should NOT attempt to put in a blow off valve (BOV). I know, almost everyone with a sweet-ass turbo'd car like ours wants a very intimidating WHOOOOSH sound. Listen, I want it, too. But that whoosh sound is WRONG for our cars; let me explain. A Diverter Valve (DV) and a BOV both accomplish the same task: they prevent compressor surge by allowing the air between your turbo and throttle plate escape to somewhere other than back out through the turbo when your throttle closes. i.e. its a place to put the boost you just made but dont need, since your throttle is closed. Our cars use a Mass Airflow Sensor (MAF), which meters all air entering the system, which not all turbo'd cars use. A DV routes the air back into the intake when your throttle closes so that it can go through the system as it was intended to. If you were to use a BOV and dump to the atmosphere, you are removing air that has already been accounted for from the system, screwing all kinds of shit up.
That WRX next to you (which also shouldn't have a BOV in it) is missing air that the engine was expecting by dumping it into the atmosphere, messing with the air/fuel mixture. Yes, you CAN make it work, but it is difficult, costly, and the car will most likely not run as strongly as it could with Diverter Valves.
Now on to some more details:
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Stage 1: Chip.
Generally 320bhp. Used: $200-$500, New or Custom: $600. Easy to find used.
-APR: is the “smoothest” and most “like stock” in its power curve, boosting to 18 or 19psi these days, but older software will be 17-18, tapering off to 15 or 16. Generally claims 320 bhp. You know you have an APR if you can change “programs” by holding in your cruise control button for 5+ seconds while the ignition is on but the car is not running. If your CEL starts blinking after holding it for 5 seconds, you have an APR chip.
-GIACX: is the most aggressive. Boosts to around 19-20psi now, tapering to 16-18 which is really getting out of the efficiency range of the K03 turbos. People do love this chip, though.
-REVO: I don’t know anything about it. It’s probably similar to the APR.
Stage 2: Chip + Catback Exhaust.
Nets you another 7-11 bhp. $500-$1,500 for the catback
-AWE Twin1 or Twin2: The Twin1 is a great , very aggressive sounding exhaust. Around $1,200
-Vibrant: Also pretty aggressive sounding, very good value for the money. Not quite as much flow as the Twin1, but it does sound very good, if not a bit more tame than the Twin1. $500-$650.
-SSAC: Cheap. Sometimes it fits, sometimes it doesn’t. Since they’re so cheap, it usually works out to be cheaper to take it to a shop and have them fix it up to make it fit, but sometimes it will run you extra. Kind of luck of the draw. It’s a copy of the Twin1, but comes as a FULL TURBOBACK with NO cats, so if you need cats you’ll have to buy them from somewhere for extra. These will throw a code without cats, so you’ll need to do some fancy things with your O2 sensors like run spark plug non foulers ($5). If you have a welder and know what you’re doing, this is a no brainer because of how inexpensive it is. People are often selling the DPs or test pipes in the classifieds. $400
-Milltek Super Dual: Much more “refined” sound. Aka a lot less loud. $1,300
-Borla: Also quieter and more refined. $800
Stage 2+: Chip + Catback + DownPipes (aka Chip + Turboback)
Nets another 20-30 bhp and helps turbos spool quicker. $0-$2,000 for the downpipes/turboback. You generally don’t need 3” DPs until you have bigger turbos, but it can’t hurt.
-Piggies: Home-made downpipes using the stock DPs: you take them off, gut the precats out, relocate the front O2 sensors or use spark plug non-foulers on them. They can net you a nice power increase on the stock turbos. You can also buy piggies from VAST for $300 or something like that, or find them used in the classifieds. $0-$300
Link to making piggies: http://www.audizine.com/forum/showthread.php?t=231301
-Other DPs: Tons of places make DPs. I don’t know many off the bat, but I think they’re generally all fairly similar. R.A.I, 034, and many others make some damn nice ones. Most 3” DP sets cost around $1,000-$1,500.
Stage 3-: New Turbos without fueling/proper intercoolers. 300awhp-350awhp $2,000-$4,000
Stage 3, 3+, 3+++++: New Turbos with proper fueling, tuning, ICs, etc. 375awhp-"smoking 996TTs" $3,000-$$HOLY F$@K
-K04s: 375awhp-430awhp. Some make more some make less. $3,000-$7,000 +
-RS6s/Tial 605s/GT2554s: 430-500+. They can get you 450 without much trouble on a stock block, and can get to 500whp or over with decent tuning/race fuel/meth. Anything at/near 500awhp you'll want to do rods on the engine which can be done cheaply, but can also end up costing $5,000+ when you decide to replace other things "while you're in there" when all is said and done. $5,000-$12,000
-Big Garrett Turbo (GT)/Tial 770/Single Turbo: 500-???whp This is kind of limitless, because everything starts to get all custom in this range. With some GT kits you can get away with just rods, that’s the 500-600awhp range. After that, you better have a damn good tuner, or it’s time to build the whole engine. The engine should probably be fully built. Many do 2.8 heads, and most upgrade the valvetrain to rev higher and enjoy the powerband. This thread doesn’t need to get into big GT kits. $8,000-“the family farm.”
End Stages.
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If you have the cash and the know-how, go stage 3 right off the bat and make it easy. Get a turboback exhaust, pick up some K04s, some Side Mount Intercoolers or a Front Mount, fueling and a tune, a new clutch (clutchmasters or southbend), and a lightweight flywheel if you feel so inclined. Parts can run you between $3,000 and $7,000 for that list. Labor is another $2k-ish.
Many will argue that K04 days are over, and you should just skip right to RS6s or tial 605s, but the reality is that it is definitely a lot more money to do that. You end up spending a bit more money everywhere, because a "go big or go home" attitude takes over. If you can scrape up a few thousand extra dollars, I would definitely go for bigger turbos, but a strong K04 car will still probably be faster than any car you've been in previously. Strong K04 cars can still do the 0-60mph in <4 seconds, and have done 1/4 miles in <12 seconds. Fastest that I know of is 11.1, but that was totally decked out.
Basic Parts list:
K04s: $2200
SMIC: $1200-$1,500
Fueling: Pieced together: <$1000, packaged: $2200, but a tune usually comes with the fueling package (VAST/EPL/etc)
Tune: $600-$$$$$$$$
Now, here’s where things start to get messy. You should probably do your motor mounts while you’re in there. You need to upgrade your fuel pump, do a timing belt change and other maintenance too. Things add up very quickly. Lets move on.
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Intercoolers: They keep your engine cooler, prevent it from exploding, allow you to run some more boost, and are generally a necessary upgrade when you do turbos. If not, you’re wasting your money blowing hot air into the engine.
Quick summary: AWE or ER Side Mount intercoolers or similar are always a good bet (ERs are the biggest, RS4s/cxRacing are the lamest). FMIC is significantly less expensive ($300-$600) than SMICs but comes at another cost. Slightly slower spooling from the extra piping, you have to cut up your front bumper and bumper supports to make it fit, and you typically have to give up your fog lights. They do cool the car damn well, though.
Side Mount: Generally fit in stock location and look stock. Recommended for those of you in SoCal.
-AWE SMICs: A nice happy middleground. PROVEN to work extremely well, fits in the stock location with no modifications, yadda yadda. $1200-$1,400
-ER SMIC: The biggest and baddest SMIC. Huge. May require some trimming to fit. Still fits in stock location. I believe that if you have an RS4 bumper it’s a fit issue, but with the stock bumper it fits. Also, they come with carbon fiber shrouds that look pretty BA. $1,300-$1,500
-RS4 SMICs: Why waste your time and money? Expensive (don’t remember how much) and don’t cool as well as the AWE, ER, or the FMICs out there. Unless you’re only doing K04s or keeping K03s and came into them very cheaply, pass.
-cxRacing SMICs: lol.
Front Mount:
-JHM/VAST: The JHM FMIC is actually an ebay core, and JHM has gone through the trouble of making you some nice mandrel bent piping. Extremely nice pricing compared to the SMICs, and have the same or better cooling properties but the FMIC comes at another cost. Slightly slower spooling from the extra piping, you have to cut up your front bumper and bumper supports to make it fit, and you typically have to give up your fog lights. They do cool the car damn well, though. $400-$600.
-cxRacing SMIC: lol. $350
Suspension: Coilovers and/or Sway Bars
Summary: If you want to keep up with most decent cars you'll want to do suspension for sure, though I've survived a while without it, it bugs me more and more every day. H&R coilovers are good and stiff for the money. stasis streetsports are good (they use koni shocks) but are on the softer side (still an infinite improvement over stock.) For something tighter, vogtland GTs and stasis tracksports are good.
hotchki (h-sport) rear sway bar also makes a huge improvement. You can do a front sway bar, but the front is already pretty majorly beefy.
Coilovers: What’s the difference between Coilovers and Shocks/Springs? Not much, other than the fact that a coilover is a shock/spring set that was engineered to work perfectly together. That means no resonant oscillations etc, etc. A shock and spring combo that’s not a coilover kit, was NOT designed to work together and may start to act stupid at high speeds. Most of them are probably totally fine, but suspension is something that I don’t like to mess around with.
-Basic “Street” Coilovers: H&R, stasis streetsports, some Vogtlands, KW V1. If you just want a firmer ride and to reduce brake drive/launch squat, this is for you. Handling will be way, way better than stock. I know that at least the streetsports are adjustable (dampener adjustable, so you can adjust the firmness and the height a bit) but they have to be off of the car. $1,000-$1,500.
-Street/AutoX/Light track use: stasis tracksports, Vogtland GTs, KW V2. Run from $1,500-$2,000. Firmer, kills more body roll, generally better. Can be rough on crappy roads. Here’s to you, Boston.
-Track use: Bilstein PS9, statsis motorsport, vogltand something or other, and KW V3. It should be apparent which suspension is designed for the track. They’ll be the ones priced epicly high. Not recommended for street use, though I’m sure some of you would be happy to have them on the street. I would. Can definitely be “jarring.” $2,500-$3,000+
Sway Bars: Reduce body roll, improve handling
-Hotchki: Is the best. 22mm rear, 35mm front. Comes with the links and all that jazz. That’s good because sometimes the linkages get all screwed up on the originals and need to be replaced. Rear: $380. BOTH: $480
-H&R: 21mm rear, 32 mm front. Doesn’t come with the linkages. Perfectly fine otherwise. $220 rear, $280 front.
-Neuspeed: 19 mm rear. Comes with the linkages/subframe stuff just like the h-sport one does. $280.
Stopping:
Big brakes are great, but most can survive without them. If you're tracking the car you'll want them. You can simply pick up some of Adams Famous Rotors (search the forum) for his drilled/dimpled/slotted rotors ($350 for all 4) which look great and do improve braking and reduce brake fade compared to stock. Some hawk pads will help too. Hawk HPS for street use/some autoX, HP+ the track. HP+ have a minimum temperature and don’t bite hard until warmed up, so be cautious using them on the street. There are plenty of other pad brands, but a lot of us use Hawk.
For Big brakes, people do cayenne brakes. There's the standard Brembo and stoptech, as well as Alcon (by Stasis), AP Racing. The Cayenne/B7 kit that JHM sells is a particularly good bang for buck right now, but things change regularly. BBK are $1,200-$3,000
Misc:
The very first god damned thing that you should do is get the JHM "solid" short throw shifter. Best mod I've done. The stock shifter is so sloppy it’s a disgrace, and all of your fiends will make fun of you for having a big rubber mallet for a shifter. Put in the JHM shifter. There, now you are the Big Leage Chew, and everyone else is just the baby school. Remember that.
Boost gauge: is super important if you're running higher than stock boost. I really like the Podi for its location, color match, and it's less than the AWE boost gauge. The AWE is great if you like the location and don’t mind spending more on the gauge. Most people agree that the AWE is the most “stock” looking, but I don’t really think any car looks stock with a big ole boost guage in one of the AC vents, but that's just me. Both are great choices. EFU also makes a "boost gauge" that works using your stock Driver Information Screen (DIS). I've never seen one in use, but it seems pretty cool.
Drive Train Stabilizer (DTS): Hooks up to your drive train to make that shit more stable. It is what it says, and it does a good job. Slightly reduces your car’s clearance, but it’s very, very worth it. AWE, ASP, and JHM all make 'em. $250-$350
Diverter Valve: They go bad on high mileage cars, and they’re easy to replace yourself so just do it.
-Bailey: Super high quality. $150 each.
-Forge DVs:
-OEM DV out of the Audi TT: The 710N or the 110 is a very nice upgrade over stock, that many people use with great success.
Throttle Body Boot: The little rubber stock TBB tears under high boost, and sometimes under normal boost. Samco makes good ones, or you can get the eBay “Autobahn 88” ones which require a bit of trimming to make them fit, but I know folks using them and it’s not so bad. Same quality, just the fit isn’t as good.
F-Hose: Same as the TBB, but not all S4s have them. Check.
Motor Mounts/trans mounts and Snub mount: 034, APR, or STERN. These vastly improve feel of the car. It's part of the overall effort to "tighten everything up." $300ish
Sport Pedals: The stock accelerator pedal is recessed enough that heel-toe downshifting can be difficult/impossible. Some nice sport pedals can help mitigate that problem. There's plenty out there, including AWE, SRP and others. I'm a big fan of the SRP ones, which also come with an AZ discount.
See: http://www.audizine.com/forum/showth...&highlight=srp
Clutch: If you’re going stage 2 or 2+, and even stage 1, you’ll probably have to upgrade your clutch eventually or immediately. Avoid the RS4 clutch. Mine slips when I launch. Lame. Go with clutchmasters or southbend. If you go stage 3, get the kevlar or ceramic versions of either of those brands. If you do well over 500whp, you'll want a twin disc. Kevlar is a minimum requirement for stage 3, but it has its drawbacks. Many people also used the VAST Stage 3 clutch, which is ceramic, with no trouble. $600-$1000, then over $2,000 for dual clutch.
Lightweight flywheel: Spin up faster, but lose some momentum for your launch. It’s a tradeoff. It also makes quick shifting more pleasant as RPMs drop faster. Yes it’s normal to hear chatter with a LWFW.. $400-$600.
Water/Methanol Injection: Running a Water/Meth injection is a great way to gain some HP (by increasing your octane from 91 or 93 to closer to 100) and lowering your IATs (incoming air temperatures). This helps reduce the risk of detonation presenting 1 of 2 scenarios. You can gain a bit of power and be happy with your new, safer setup, or you can use the higher octane and lower temps to advance your timing and get more power out of it. It all comes down to your tune. DevilSown and aquamist make good kits, and VAST sells a DevilSown. If you’re on K04s, the 190cc injectors are fine. If you’re on bigger snails, get bigger nozzles.
DarIntake: The "DarIntake" mod basically involves cutting a hole into the bottom of your airbox, effectively creating a cold air intake. This nets you around 5-10 hp, and should be supplemented with either an AWE S-flow or a nicer panel filter.
link to mod + custom S flow mod: http://forums.audiworld.com/showthread.php?t=1491134
Good tuners: VAST, EPL, SSP, APR, AWE. Most people go with VAST, EPL, or SSP.
Just to make things clear, you don't have much to worry about on this drivetrain until you're very high powered or if you're driving it wrong. Slip the clutch if you launch, and all will be well. Block is good for 500whp, tranny is good for a lot more if you know how to shift.
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Stage 3 more in-depth parts/costs:
Here is my parts list for going RS6. These reflect prices that I was able to get after a lot of hunting and dealmaking and what have you.
RS6 Turbos $ 3,200.00
Flanges
Gasket
Hardware Kit
VAST Inlets $ 199.00
VAST Fueling Kit $ 2,380.00
Hitachi maf wiring, 90mm MAF sensor, RS4-Hitachi MAF housing
Updated green coolant temp sender w/o-ring/clip
N75 valve
Colder Spark Plygs
Fuel rail hardware
RS4 airbox modified for more flow
RS4 accordian hose w/clamps and
Siemens 630cc/min fuel injectors
AWE SMIC $ 1,075.00
Rostin Rod Set $ 1,250.00
034 Coated Rod Bearings
034 Coated Main Bearings
Electronic Fan Kit $ 195.00
CluchMasters FX400 $ 700.00
034 Engine Mounts $ 300.00
Links to the vendors that sell things that I've mentioned here:
JHM: http://www.jhmotorsports.com/
VAST: http://vastperformance.com/index.php
034: http://www.034motorsport.com/
PureMS: http://www.purems.com/products/index.php
SuperiorHP: http://www.superiorhp.com/catalog/index.php
AWE: http://www.awe-tuning.com/
RAI: http://www.raimotorsport.com/
ECS: http://www.ecstuning.com/Audi-B5_S4--2.7T/
Very good resources to check before you post a question.
Everything:
http://www.s4biturbo.com/
http://www.vaglinks.com/VAGLinks.asp
http://homepage.mac.com/edyjun1/S4/index.htm
http://s4wiki.com/wiki/Main_Page
http://www.nogaroblue.com/8638/8762.html
http://www.infobarrel.com/Audi_S4_(B5)
Links to all of these links and more in one thread:
http://forums.audiworld.com/showthread.php?p=13260897
Info on Suspension:
http://farnorthracing.com/autocross_secrets6.html
Info on Wheels:
http://sanders-stuff.com/Cars/S4_Wheels/s4_wheels.html
http://www.s4wheelgallery.com/
Exhaust System Info/Theory:
http://www.audiworld.com/tech/eng28.shtml
DIY info outside Audizine:
http://www.audidiy.com/b5s4.html
http://www.audiworld.com/tech/ext.html
Specs:
http://www.audiworld.com/model/s4/01/specs.shtml
OEM Parts Links:
http://forums.audiworld.com/showthread.php?p=1900084
Good luck...
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and +rep for you sir
Originally Posted by zx6r1033
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