So the S3 K04 needed some modifications to fit on my 2006 A4, including:
- Diverter valve relocation since the turbo was not machined for it
- Drilling and tapping the turbo for the diverter valve to have a place to inject air into when active
- A custom charge tube, which now connects to the top of the intercooler instead of the bottom
- The bottom intercooler transfer line being clocked at a different angle so it can now connect to the bottom of the intercooler
- K04 exhaust flange is larger than the K03, so weld holes and drill+tap new ones (in stainless!)
This is the mostly finished product, you can see the custom diverter valve mount with a rubber tube that hits a 3/4″ NPT nipple that was added to the turbo before the compressor wheel.
The diverter valve relocate was made entirely from Schedule-80 tube, from the 1″ tube connecting at the bottom flange and and side flange (for the re-circulation tube) to the 2.5″ tube that brings it all together. Everything has been opened up mildly on the lathe, you can see the lip left over from the original thickness.
The top view shows the lip a little better, along with a slight angle cut to make welding the top flange for the diverter valve easier. The 1″ pipe entering this pipe was cut on a ~$45 end tubing cutter from Harbor Freight which worked better than expected.
Here’s a quick mockup of the assembly. I did mockups in PVC before machining anything.. partially because I was bored, partially to make sure my ideas would work correctly. The plate on the “top” of the relocate will have the small hole drilled out to 1″ to fit a coupling into the intake charge tube. The other long 1″ pipe actually seen in the picture will be cut short to allow for the recirculation hose to connect to the turbo.
The flange, modified. The outer bolt hole you can see in the lower left is the original K04 size. The other side needed to be cut off to avoid hitting the motor mount. Unfortunately I had some issues drilling the new top two holes after welding it, probably due to the type of rod used. The studs wound up getting welded in, but the important part was we now have a flange that fits the stock catalytic converter or 2006 A4 downpipe!
The car runs, at first it ran FAST and would pick up >15psi of boost with spikes above 20psi. It was pretty great, even if it was running lean. APR K04 tune incoming along with bigger injectors.
Keep in mind lots of stock parts needed tweaking, some of the oil/water lines needed to be bent slightly although they happily bolted up to the turbo.
The charge tube is a tight fit, it just about touches the radiator, AC lines, and the frame. I should’ve used 2″ pipe here instead of 2.5″ and tried to find some with tighter radii, but it worked out. Not the 2.5″->2.0″ reducer on the intercooler. I just welded some exhaust pipe on the core support to point it as well as I could at the intercooler, the silicone hose I used isn’t kinked so it appears everything turned out pretty good.
So my water pump replacement turned into replacing a water pump, timing belt, thermostat, and adding a bigger turbo. It also made me buy shiny new tools, like an Ingersoll Rand 2235Ti Max 1/2″ impact gun (WHICH KICKS ASS! 1350ft lbs of reverse torque — really?!), and of course “triple square,” tools and a few sets of security bit sets for Torx bits which I’d constantly drop and find later — and smaller triple square bits (like M5).
So Audi A4, I win today. Though I’m sure you’ll break some other way. But for now I don’t have a noisy turbo, and hopefully I’ll have lots of horsepower soon.