KO4 upgrade

[s4marsh]

hi all i've just found this article about the rs4 http://www.sae.org/automag/globalview_08-00/04.htm while searching for something else unrelated but might be worth a read regarding the difference in s4/rs4 engine and also look at what the maximum boost pressure of k04 turbos. 32 psi ??? also how many people have just left the engine internals standard s4 spec and fitted k04's, have you encountered any part failures?

[okkim]

I think that most of the people haven't change internals, and motor has been working ok without failures. But I know that some people have broken rods with K04's.

So, with reasonable power (I would say less than 450 hp), and good tune you are just fine.

[Dippy]

I believe that the stock RS4 had a peak boost of 1.2 bar and typical remaps raise this to between 1.4 and 1.6 bar. Of course as well as peak boost there's the top end boost that will contribute to engine stress. Nevertheless if the K04s have a maximum 32psi boost, most cars are running well within the compressor map.

I am left wondering if Cosworth really did need to make all those changes, unless the decision was taken that although modifying the RS4 voids the warranty, Audi didn't want to get bad press about their (then) flagship performance car breaking.

I don't want to start an argument, but I'd say that for up to 450 bhp, a B5 S4 needs a lot more than K04s and a good tune. Maybe internal mods are not required, but a lot of work will be needed to improve breathing, fuel flow and cooling.

[s4marsh]

so apart from fuel+cooling and breathing you would say the internal changes are just audi/cosworth overkill? no such thing as too reliable i suppose especially like you say for their flagship model