I got a used pair of OE BW K04’s from a forum member. Despite them being low mileage, I decided to rebuild them and upgrade the compressor wheels before putting them on the car. For the wheels, I got Mamba part 010-K3A6. It’s an 11 blade wheel with extended tips, taller blades and a slightly bigger inducer. As compared to the original 4 + 4 staggered compressor wheel, the 11 blade wheel will produce peak boost at a lower RPM, at the expense of efficiency at peak mass flow rates. However, since the billet wheels are taller and have an extended tip, the wheels should flow more than the original cast wheels. I’m hoping that the combination of 11 blades, extended tips, taller exducer tip heights and taller overall blade heights will result in greater peak flow and faster spooling than the original cast K04 wheels. The extended tips add an additional 6mm, giving an effective exducer size of 56mm and the exducer tips are about 15% taller.
Fitting the wheels was more difficult than I originally anticipated. To fit the new wheels, I thought all I’d need to do would be to open up the inlet of the compressor cover to accommodate the .1mm larger inducer. However, due to the taller height of the wheel, the entire profile of the compressor cover needed to be machined. I started off by digitizing the profile of the original K04 compressor cover.
I then measured the additional depth that the compressor wheel needed to maintain the same clearances as the original cover, about .0012″, and machined the cover.
After the new radius was cut, I put the cover in my lathe and opened up the inlet.
The clearance between the radius of the wheel and cover looks dead on, but I don’t have any way to measure it. Unfortunately, on one of the turbos, I ended up with a bit more clearance between the cover and inducer than I was shooting for. I was shooting for .0012″ and got .0018″-.0020″. The clearance on the other turbo is .0012″-.0014″.
I’m sending the turbos to G-Pop shop to have them VSR balanced.
I bought the rebuild kits from Turbo Lab of America’s Amazon store and found the quality to be very good. The parts are extremely well manufactured – the thrust collar in the kit is larger than the original and the thrust bearing is a full 360º with 3 oiling holes, unlike the original windowed, single oil hole thrust bearing.
