Some time ago I did testing and found that the intake air charge temperatures would get pretty high after hard running or because of heat soak while sitting in traffic. In my search for ways to reduce the temperatures I looked into fans mounted on the back of the intercoolers and intercooler misters which spray water in front of the intercooler to reduce air charge temps. The problem with the fans is they would be of little benefit if the car was already moving. Right around the time I was pondering solutions Autospeed.com released a new product they called the "Intelligent Intercooler Mister". What this handy controller does is monitor the IC temperature relative to ambient temperature and fuel injector duty cycle (they call it the fang factor) to determine just how hard you're running the car. You set a temperature threshold and an injector duty cycle threshold... when both are exceeded the controller turns on the spray.
The benefits of this controller are reduced water usage and better control of intercooler temperatures thanks to its logic. No water is sprayed when on boost if the IC is already cool, spray continues between shifts and, if the logic decides you've really been hammering on the car, continuing to spray after you're off the throttle to get the IC temperature back in line. A very slick system. Autospeed.com has a 5-part series that explains the theory and operation of the controller--very good articles, highly recommended reading.
I decided to use the headlight washer pump to drive the spray nozzles since I don't like them spraying water back on the hood of the car anyway. Other benefits of using the existing pump are it's already wired, it has an adequate water supply with a driver warning when water gets low (the 4.9L windshield washer tank) and the existing plumbing for the headlight washers is perfectly suited for IC mister duty. Plus, room under the hood of the S4 is so scarce there's little room for an additional water tank or pump. For the water supply I'm using distilled water to prevent calcium and lime deposits from building up on the intercoolers... water in my area is very hard.
For spray nozzles I contacted accuspray.com for low pressure hollow cone nozzles, check valves so the water wouldn't drain out of the tank when not spraying, barbed elbows and retainer rings that bring it all together. The nozzles are perfect for this application.
This mod has been quite popular... so popular that Accuspray now has a part number for all the parts listed above in one tidy, easy to order kit. The number for the kit is "ICK" (for Intercooler Kit). The kit is not listed on the website so it's best to contact them via phone (1-888-492-6648) if you wish to order parts.
Intercooler mister controller available at Autospeed.com
One note, when I ordered my controller from Autospeed.com it took 56 days to arrive. After several weeks of waiting I was told demand for the controller was much greater than they expected and mine was backordered. If you choose to order one ask about availability to avoid any surprises. : )