Archive for April, 2011

The new turbos, part 2: Electric Bugaloo

April 4, 2011 1 comment

When we last spoke, I left you re-directing your browser to Chris Ostberg’s fantastic B5 S4 resource site,, saying he was selling something interesting.  I was on Quattroworld checking the classified when I saw a post from Chris.  Chris was selling his K04-K16 hybrids.  Holy S(4)!  His description was optimistic, that the turbos were serviceable but he personally would rebuild them before installing them (see last time’s discussion on installing used parts), and I knew I could rebuild a K04 for between $300 and $400, so we made each other offers we couldn’t refuse, and the turbos became mine.

(All the bad things we talked about last time – owner abuse (did you watch any of his videos? How about them Nurbergrings?), shaft play, foreign object damage)

What is a K04-K16 hybrid you ask?  Well, a hybrid turbo is when a company that doesn’t manufacture a certain turbo thinks they’re smarter than the company that does manufacture said turbo, and decides they’ve come up with a superior combination to what the silly engineers could.  In this case, we have a K04 (from the European hot-rod of the S4, the RS4), modified to accept a Porsche 911 Turbo (996) compressor wheel.  Why would you want to do this?  Because Porsche Turbos are fast?  Yes.  Why are they fast you ask?  Well, it’s obvious (from Chris’s site):

(Quite the obvious visual statement)

K16 is big.  Now they’re doing hybrids with 911 Turbo (997) wheels, but before the 997s came out, 996 was what it was all about.  The first thing you notice is the K16 is bigger.  Yes.  The second thing you notice is that it has more blades (12) than the Audi wheels (8).  This is important.  Size matters, but the extra blades make the K16 more efficient.  Basically, the extra blades get a better grip on the air and increase the flow rate of the wheel at a given speed.  The lower the speed, the “faster” the spool (because you’re targeting a lower speed), and the happier the bearings in the turbo.  We’re talking about speeds in excess of 150,000 rpm, so lowering that is a good idea.

Why not just put a K16 in there?  It won’t fit.  The whole point of the hybrid in my case is to accommodate the very confined engine compartment (not a lot of room to redirect the plumbing of the turbo-we can’t even fit a physically larger unit in there), while having something better than a plain-jane (PJ) K04.

Next question: why not put a couple of GT25s in there?  Yeah, about that.

From Chris’s site – I’m tired of my dirty pictures.  Well, not those dirty pictures, the pictures of my dirty unit.  Well, not that dirty unit, the filthy turbos.  Yeah.  Nailed it.

See that funky flange?  That’s where the turbo connects to the exhaust manifold.  The downpipe flange is also unique (to everyone but VW, Audi, and Porsche).  Changing all that to get a Garrett in there is not worth it (because now I need headers and a new turbo-back exhaust system?  Why?  I thought I was upgrading the turbos?), so most guys make do with K04s, hybrids, RS6s, weird “eliminator” combos that advertise a Garrett cold side on a Borg Warner/KKK hot side, and now the new Frankenturbos (which is what Chris was trading up to).  Anything that’s not BW/KKK will have fitment (and potentially quality issues as have been reported on the forums), so I wanted to stay with the tried-and-true (even if it is tired-and-true) K04-based system.  RS6s are a safe choice, but they cost more, and they start to border on a selection too large for my platform.  Too large you say?  How do you know?  Well, because of the turbo sizing calculations I did of course.  Oh, you don’t know how to do that?  Why didn’t you say so?

– Jeff knows all about how to blow bigger…

Categories: Cars, Jeff