[Biturbos4] All causes to turbo failures known?

dap128 dap128 at hotmail.com
Thu May 13 20:52:59 EDT 2004

> Interesting. They looked identical to me, now I wonder if there are
> different kinds of K04's ...
For the S4, there's only the K04-25 and K04-26 (which are the OEM units for
the RS4).  A few tuners are starting to work with hybrids of the K04
housings and exhaust wheels mated with K16 or RS6 compressor wheels, but
those are just starting to gain popularity (and the housings are still the

> Any idea how much larger the outlet is? Are you sure it wasn't just
> different outlet pipes leading to larger intercoolers? Unfortunately I did
> not have time to measure anything..
I don't have the measurements but I've seen pictures posted showing the
measured difference.  And its not the outlets (I mistyped, if thats what I
wrote) but the inlets that are larger... the larger piping goes from the S4
(or RS4) y-pipe to the compressor inlets.

> However, ATP has been mentioning mirroring this information, as well as
> suggesting using a pair of GT25s garrett turbos instead of K04's...  I'll
> have to find out more about this.
I've seen ATPs indications on developing a GT25 kit and would certainly like
to see that development.  That's why I said at present there isn't a kit
using larger turbos... hopefully something will materialize.

> : However, the most significant and important difference is in the shaft
> : the turbo itself.  The K04 has a reinforced shaft and should hold up
> : better than the K03 does.  Indeed the failure that you experienced with
> the
> : shaft would most likely not happen due to its more robust design (in
> : addition to the fact that it is made to run higher boost levels than the
> : K03s are).
> Details... details.. reinforced is a very relative marketish sound.. :P We
> talking larger diameter? A larger diameter will equate to greater bearing
> surface speeds... (bad)
The diameter of the shaft is the same but the temperature restrictor (hollow
portion within the shaft) is a different shape/size, thus leaving more solid
material in the shaft and making it less prone to failure.  I've seen
schematics of it posted on Audiworld, but again, I don't have a link handy.
If I can find the diagram, I'll be sure to send the link to this group.

> : The K03s appear to be somewhat underdesigned for the 2.7T motor, hence
> : failures.  Replacing them with K04s seems like a no-brainer to me, given
> : that the cost is about the same and the K04s are much better suited to
> : engine.  And as of yet, no one has come up with a way to install any
> : turbochargers without relocating them and significantly altering the
> intake
> : plumbing ($$$).
> What makes you feel they are underdesigned?
> They work fine on a 1.8T, and a pair of them with the same volumetric
> effeciency would support 3.6 liters with the same reliability. They're
> feeding less displacement at the same boost levels on the 2.7. We should
> getting more reliability with less cubic inches to support, but we should
> also get more lag if everything is equal...
> You'd think I'd have access to tons of technical information on this. I
> don't... :P

I just think that they are underdesigned in the 2.7T due to the high rate of
failures even on stock boost.  And I don't think they are necessarily
underdesigned with respect to the boost levels run.  I think it has more to
do with how well they handle the excessive heat due to their placement on
(under) the 2.7T.  On the1.8Ts the turbos are much more well placed.
However the compact nature of the 2.7T makes this impossible.

And even without access to tons of technical information you are still very
knowledgeable and an asset to this list and all of your dealership
customers.  If all techs were as knowledgeable as you, a lot less people
would have complaints with Audi service :)

-Dave Pramanik

More information about the Biturbos4 mailing list