No need to spell check, this is a rough draft. Final version will have pictures. I would really like to make an exhaustive list of vendors and want to know if I left anything out or of if my science is way off. Thanks.
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Intercoolers:

How it works: The intercoolers are essentially air to air radiators used to cool the pressurized air coming from the turbo chargers. Since turbo chargers are driven by exhaust gases they become incredibly hot and a portion of this heat is passed to the intake air as it pressurized. The temperature of the air going into the combustion chamber directly influences the power output of each combustion cycle. Explaining this requires going into detail about how combustion reactions work, but as a general rule the colder the air the greater the potential output of the motor. Intercoolers allow your car to maintain peak operational efficiency and prevent premature detonations (the fuel in the cylinder ignites before the sparkplug fires) which can damage engine components.

That being said, bigger intercooler do not guarantee performance gains. Increasing the size of the intercooler core before increasing the output of the turbos will actually reduce performance and shorten the turbo life-span. A bigger core means a bigger volume that the turbos need to pressurize to maintain a particular boost level. All intercoolers will create a boost drop which needs to be compensated for - the larger the volume the bigger the compensation and the harder the turbos will have to work. If your turbos are already pushing the maximum air volume that they can (or are limited to by the ECU program) then they will not be able to compensate for the pressure drop across the IC(s) and your power output will suffer.

The stock intercoolers are generally considered sufficient for handling factory power levels and boost. Upgrading to larger intercoolers is recommended with a chip upgrade but is not absolutely necessary. Maximizing the core volume is appropriate only with a K04 or larger turbo system.

Failure Symptoms: The same as with any other boost leak (see boost leak section)

Location: The top of each intercooler is almost directly underneath and slightly behind each head light. From the bottom, the intercooler on each side is directly in front of either front wheel well on the engine side of the splash guard.

Upgrades:

The main consideration when upgrading intercoolers is the volume of the core. This can be determined by simply multiplying the width, height and thickness of the intercooler core – this is different from the overall dimensions of the intercooler which would include the end tanks or any mounting brackets and so on.

For comparison: The stock core measures 8.5" x 6.75" x 2.688" for a volume of 154.224 cu/in. per intercooler and a total volume of 208.448 cu/in of combined volume. The ER (evolution racing) SMIC measures 10" x 8" x 4.5" for a volume of 360 cu/in per intercooler and a 720 cu/in of combine volume. This is the largest SMIC upgrade that you can purchase for this car. The popular cxracing or JHMS FMICs measure 22" x 11" x 3" for a total volume of 726 cu/in.

Aside from increasing the core size, any worthwhile aftermarket IC will have aluminum end-tanks instead of the plastic ones on the stock set. The plastic end tanks are prone to leaks, something that is not an issue with the metal ones because they are welded to the core.

The other major factor in choosing an intercooler upgrade is whether to go with a front mounted intercooler (FMIC) or a pair of aftermarket side mounted intercoolers (SMICs). As with all things, both have benefits and drawbacks.


FMIC: as the name suggests, this is an intercooler mounted in front of the engine, specifically on a B5 S4, in front of the A/C condenser, displacing the stock auxiliary fan and power steering cooler.


Benefits: Besides the increase in core size, the primary reason to convert to a FMIC set-up is the increase in airflow to the IC and the resulting drop in overall temperatures of the charged air entering the combustion chamber. An FMIC kit is usually also the most cost effective – you can find complete kits with piping and hardware for under $400 on ebay.

Downsides: Installing an FMIC on this car requires some significant modification to the front bumper support, grille inserts and fog light mounts and requires the removal or replacement of the auxilary cooling fan and stock power steering cooler. In addition it will disable the headlight washer units unless the hoses for these are rerouted from their stock locations. Another disadvantage of the FMIC design is that it increases the number of connection points two-fold over SMICs thereby increasing the potential for weak points and boost leaks.

The final disadvantage is the necessity for "crossover" which means that the pressurized air from the driver's side turbo actually ends up going in the passenger's side of the bipipe and vice versa. This is not a problem in and of itself, but because this is a dual turbo system it means that the FMIC actually has 4 temperature zones instead of the usual two. The practical downside of this is that the hot air inlet from one turbo is on the same side as the cold air outlet from the opposite turbo and some heat exchange occurs.

SMICs: Side mount intercooler upgrades must be done in pairs of identical units. Do not mix intercooler core sizes!

Benefits: Installs in the stock location and has fewer connection points than a FMIC. Overall, the install is significantly simpler than for an FMIC although many upgraded SMIC kits do require some trimming of the plastic frame under the headlights for proper fitment. Theoretically they are also safer since you do not have to chop up the aluminum bumper support. With a large enough kit and proper direction of airflow using shawls or other methods this system can match or even exceed the cooling of an FMIC.

Downsides: The main downside is the expense. Only the very largest upgrades (ER etc) compare to the core volume of a FMIC kit and they typically cost 2-3 times more.

 

Very nice and thank you. If I may suggest..
1. if possible please add some more info / detail in terms of how one go about calculating the optimal size of the SMIC based on boost, turbo size and flow.
2. if possible fitment issue for each IC. (ie: Trimming needed for stock S4 front bumper for RS4 SMIC or not
3. if possible user review link for different brand IC.
4. if possible, please explain/state why eBay intercoolers are cheaper. Though many vendors uses eBay ic core.
5. if possible some real comparism between branded and eBay intercoolers.
6. May be a chart that states based on turbo size , desired boost.. what size of IC?
Just my 2 cents. Again excellent work.

 

Hey Tazz - thanks for the input. I will try to work this info into the guide. Here are my best answers to your questions at the moment:

1. I'm sure there is a formula out there somewhere to determine the optimal size of an IC based on those factors. Since there are really just a handful of core sizes and common turbo swaps available for this car the best course is just to pick the correct configuration.

Take the stock RS4 intercooler core size: it is only 162.54 cu/in, not that much bigger than stock S4, and only 325.08 cu/in of total core size. This is less than a single ER intercooler yet it was deemed sufficient by Audi engineers to handling cooling for the K04 turbos. That is not to say a bigger IC would not offer improvements for a K04 set-up but there is absolutely no reason to run ER SMIC on a stage 2 S4.

I would go no bigger than the cxracing smic core size for a stage 1 or 2 S4. I would avoid RS4 IC's altogether because the gains are so minimal. AWE, ER or any FMIC or other really large core size is only needed for Stage3 or 3+.

2. Can someone comment on the modifications needed to run an FMIC with an RS4 replica or genuine bumper?

As for the SMIC, you don't need to trim to install the RS4 or cxracing SMIC, these will fit in the existing space. The AWE and ER (and similar) do require some trimming of the plastic around the IC mounting location and may require bending/removal of the stock mounting brackets.

3. I'll see what I can come up with - in the meantime, who is running the different set-ups and what do you like/dislike about your IC upgrade?

4. That's easy: made in China. Probably by starving Chinese children who have never seen sunlight or breathed fresh air.
This is ok, because asian people have no souls, I asked my ex-gf (who is Chinese) if this was true and she confirmed it. :P

The reason ebay is cheaper is simple economics - ebay stores have no store front, minimal advertising, larger production runs and more general product lines. The same cxracing FMIC for the S4 is also sold for other twin turbo cars like the Supra and 300zx. All of this cuts the margins for the ebay sellers and allows them to sell cheaper and still make a profit.

I don't know where the vendors get their cores, but I don't believe they get them from ebay. JHM has accepted that many of their customers buy ebay cores so they offer just the piping and hardware for their kit as well. As far as I know no major vendor openly advertises that they use ebay cores in their kits.

5. I have not seen anything like this but I agree that it would be a great addition to the guide. If anyone has a link to something like this please share.

6. The best chart I have run across that kind of addresses this topic is here http://www.mnaudi.com/jprice/er_intercoolers/

 

I'm not an engineer - and I don't play one on the internet but I think one way to [help] determine proper intercooler size is by comparing flow. What cfm is your motor pushing and what can the intercooler handle.

This is a cool site http://www.bellintercoolers.com/ - I bought a core from them for a custom IC on my ur-quattro.

HTH

Brandon
'84 ur-quattro 20Vt
'01 S4

 

Thanks!

I play an engineer online and a doctor in real life. The hospital keeps throwing me out though...

 

Another thing to take into account would be pretty drop at a given flow at a given PSI.

The DUH FMIC was really good, but... It had a high pressure drop with anything flowing more than K04s. Things like SMIC or FMIC water to air would have a very low pressure drop in the core. Many more fun variables.

 

pressure drop from the air cooling down too quickly or what?

 

Good writeup. Yeah, I'd mention the disadvantage of pressure drop with the FMIC.

 

Can one of you guys fill in the blanks for me? Is the pressure drop compensated for by the turbos? Is it due to the rapid cooling, larger volume, or something else?

 

Longer passages. Alot more skin friction is what I'm going with.