frob

I finally got my hands on my new (slightly used) replacement turbo, and was amazed to see how rough the passages in the compressor housing were and the steep step in both intake and outlet. Considering that together the compressor intake and output diffuser area are about the most critical high-velocity air paths & greatly affect turbo efficiency, i decided to port/polish the areas carefully. Since i needed to disassemble the turbo anyway to thoroughly clean & oil it before putting it in, it wasn't a whole lot of extra effort.

This seems to be the late model K03-058, which is very close to a K04 in performance (215 Hp vs 220Hp, according to ***). With the 'porting' improvements, i wouldn't be surprised to see another 5-10 HP improvement, and possibly making it at least as good as a 'stock' K04.

Here's a few before and after shots.

K04-S4

Nice work and pics!

There is some significant increase in passageway diameters. What process did you use to open them up?

frob

Thanks

I just used a drum sander bit with coarse emery drums in a drill press to open up the inlet & outlet, then used wet sandpaper #220 then #320 then 4F steel wool to polish out the sanding marks. It would have been easier/better to use a lathe, but i haven't got one... yet. Hard to see but the result is a nice "bellmouth" shape, which should make for a pretty smooth transition to the silicon hoses.
In the scroll i used my dremel with various grinding bits, small sanding drum and flapper wheels followed by a fine abrasive "scrunge" bit and the same sandpaper + steel wool treatment to polish out the sanding marks.
Another thing worth mentioning is the round flat face of the scroll just outside of where the compressor tip OD is has very rough machining grooves in it, though it doesn't show in the pictures, its like running your finger over a fine file. I polished those marks out with sandpaper backed by a large wood disk (so as not to accidentally scratch the inner surface) then 4F steel wool.

Although the turbo looks mint and the shaft has very little play (well within specs) i noticed before i disassembled it that there is a noticeable clearance space between the compressor blade and the housing- much more than necessary IMO. Having more than a few thou of clearance there is also known to have a very bad impact on compressor efficiency, so i'm considering painting the area in the housing to build up the surface with wearable material like they do in in high performance turbomachinery.
Of course there is a danger in doing that if the paint every peels off you will ingest it in the engine and maybe even bend the compressor blade, so i'm not convinced its a good idea yet. I have some high performance epoxy i use on carbon fiber, with some fine chalk powder (a common filler, like in bondo) and some alodine on the aluminum before to enhance adhesion, it should work well - in theory. The chalk makes the epoxy easily "sandable" so as the bearing slowly wears over time and the compressor starts to rub, it will wear off just enough material from the housing without significantly wearing itself down. That way you can run the turbo new with almost zero clearance for maximum efficiency. Anyway not yet decided to do this or not.
What i will do though is paint the compressor scrol (outside)l in clear high temp paint and do the same with the turbine housing in black - to prevent corrosion.
I got a new stainless manifold and flexpipe to go in with the new turbo, but i think i'll get some ceramic insulation tape to wrap those and the cat before doing that. I just got back from getting stainless bolts, nuts etc to assemble all this. Not so much for looks, i'm just allergic to corrosion and hate to have to deal with seized bolts (synonymous with skinned knuckles) when working on my 'ride'.

On the intake side i'll probably be fabricating a slide-on 'bushing' adapter to to increase the OD from 1.75" to 2.75" which will seamlessly continue the inlet "trumpet" style out to the full OD. This will just be glued on with RTV, and will mate with a 2.75" silicon 'L', then some bent aluminum tube with welded fittings for all the pipes, and finally a 45 degree 2.75" silicon 'L' to the airbox. That should make for a very low-restriction intake with the smoothest possible flow into the compressor.

S4zAudihere

i have 2 ko3's out of my s4, i was wondering how hard it is to rebuild one? i'm extremely mechanically inclined, and have no fear of taking on the project, especaially because they are just sitting in my garage. (if i failed no one would know, i would just take pictures of urs and post them ) I was just wondering if it would be alright if i sandblasted the the turbos? if that's not good, how would i go about cleaning them up? degreacer?

frob

Turbos are deceptively simple machines. They can be rebuild 'DIY' fairly easily IF you know what your doing - there are a lot of gotchas and misconceptions to be weary of, that cause most people who attempt it to fail. Most experienced folks will tell you don't try this at home. If you really want to do it, do your research first.

First up, NEVER sandblast a turbo. doing so can turn it into a bomb waiting to explode into your engine. Carefully disassemble it first, and use degreaser like 'Dunk' with some scrubbing brushes on the separate components- preferably with a proper 'parts cleaner' with filter /pump for the fluid. I would avoid soaking the wastegate actuator as solvent may hurt the diaphragm, especially if it gets inside.

For proper/safe operation the CHRA must be completely clean and free of all grit and foreign matter inside & out. If you don't disassemble it (i.e. if it looks serviceable & passes inspection), you will need to use a blow gun several times to clean out the passages. When everything seems perfectly clean, rinse it in new cleaning fluid and blow it dry. Double check the passages with Q-tips. if they come out with any grit or dirt at all, especially the oil inlet, clean it again.

There are a few "write-ups" out there on turbo DIY rebuilding.
Roughly the steps are like this:
- remove and inspect compressor and turbine housing
- inspect compressor and turbine blades for signs of wear, damaged or bent blades, or rubbing on the housing and backplates.
- Does it spin freely without wobble? check shaft side to side and front to back play. this should be done with a micrometer & compared to OEM specs.

- If the turbos seem good so far, and didn't leak or overheat in prior use, the CHRA might be serviceable, worst case it should be sent out for to a turbo shop for more precise inspection & balancing. Balancing only is not expensive, most 'local' shops can do this. either way, thoroughly clean it before doing anything.

- If the turbine is damaged, then rebuilding yourself is probably not worth it, it will be a hassle & as expensive as sending it out for pro rebuild, maybe 1/2 the cost of new.

- If the compressor blade is damaged, or the shaft bearings are worn out of spec, also consider sending it out. You can get a replacement blade for $10-100 (get one pre-balanced) and install it yourself, then get a local shop to balance the CHRA ( there are 2 balancing methods, each have pros and cons - for the DIY'er, high-speed balancing after the CHRA is reassembled is probably safer)

- If the shaft & bearings are worn/ bent/out of spec, you need to disassemble the CHRA and get a rebuild kit with bearings etc. A bent shaft can be straightened by a turbo shop, don't try this at home; It needs to be true beyond our ability to measure without special tools. Before ordering the rebuild kit, measure the shaft diameter carefully with micrometers so you can order the correct oversize kit- try to get the oem kit, not the cheap knockoffs if you can avoid it.

- If the only thing wrong is worn bearings/shaft, you can carefully mark the position of the compressor & nut vs the shaft so you can reassemble it in *exactly* the same alignment later, so rebalancing isn't strictly necessary (but still a good idea)

Especially when the housings are removed, treat the turbine and compressor blades better than you would your first born baby- the slightest ding will throw them out of balance (esp. the compressor) even if there is no visible damage. These things spin at over 100,000 rpm, and it only takes a few micro-grams of imbalance to mess them up. use a piece of plastic pipe or similar to support it on the CHRA housing, NEVER lean it on the blades.

It's possible to "upgrade" the turbo with a bigger compressor wheel for higher power output, but i have no experience there, though I've studied the process.
I'll likely try that with my old turbo after the swap, if i can get the right compressor wheel 9& matching housing if necessary). If i do, i'll post it all here too.

If you end up reinstalling the turbo, its highly recommended to change the hoses & pipes too, as any crud in them can be broken loose in handling, and that will clog the turbo later, ruining your hard work. Oil it first, and crank the engine for a minute with the fuel pump fuse removed to pre-fill the hoses etc. before starting up. then let it idle for a few minutes while you watch for problems.

frob

UPDATE:

Well, I'll be....

I really didn't set out to do this but....

There were large protruding sharp edges on the turbine housing where it was cut off from the mold runners after casting, so as i was cleaning it and getting it ready for paint, i thought i'd just round those off with the grinder - wait a second, no sparks, and the metal under is shiny like.. no, can it be? stainless steel? Yes! gotta love Audi, these have high quality Stainless exhaust housings, not cast iron.

Well i got a little carried away with the grinder, and started with the sander. Wow! not quite finished, but suffice it to say it looks a hell of a lot better than the rough bluish-black sand cast housing did a little earlier. when I'm done I'll post a couple more pics. Too bad i didn't think to take a 'before' shot...

K04-S4

Agreed, stainless hotside is quality!

I've wanted to rebuild an old pair of K03's, and do something with cleaning up rough castings and open up the cold side airways while apart.

Without taking them apart, did a casting cleanup and intake airway smoothing to new K04's before installing and that worked out well.

So it's true... when the Turbo housings are apart you can really have some fun!

That is some great work and detailed info

frob

here's a few pictures taken just before installing the turbo - I'm please to report she's running better than ever; i still can't get enough of the extra torque all through the power band! acceleration is about double what it was pre-transplant. What a huge difference a working turbo makes!

Notice the extra springs on the wastegate. this is my "patented and improved" method of 'cranking' the wastegate to stay on against the extra backpressure when pushing to higher boost levels, as i will do later ( once i've upgraded the intercooler)

enjoy
P.S. stay tuned, more pictures of the engine rebuild are about to be posted in a seperate thread....

frob

Well it didn't take long for my stock DV to give up the ghost, it was 9 years old (67 in car years?) and probably never worked a day in its life until last week, so not much of a surprise when it expired an hour ago - may it R.I.P.

Update- Make that the MAF too - weird, no signs of overboosting, no other DTC's yet the MAF burned out - could it be a coincidence?

2nd update- DON'T BUY THIS CHEAP @#$%#%^& EBAY EXHAUST MANIFOLD !!!! Welds cracked on the collector above the turbo flange after a little over week on the road. I really wish i had done some research before buying this, a lot of others it seems have discovered this is crap the hard way too. Now i have to swap it out again, good thing i hung on to the stock one. This is going to be a real B*** because the rear turbo flange bolt on this piece of crap is completely inaccessible without completely removing the turbo.