Really following on from a thread started last week on hybrid turbos for the A4, I thought I would actually get round to starting my thread as I've started to make some head way on the turbo build.
So I'm normally found lurking on the 8L forums and have been building hybrid turbos for a little while, mainly again for the 8L and 8N platform. In the course of learning as much as I can about Hybrids and the like I found that there really is a limited choice of decent Hybrid for the A4 1.8t engine. S4 and RS4 all seem to do well but the poor 1.8t seems to have got left behind.
Most of the companies that offer hybrids for the S3/TT etc do offer them for the A4 but simply not on the same level, now whether this be demand or mechanical issues I don't know but when you think the 1.8t engine is the same throughout the VAG range the question has to begged why can you now get a 320bhp hybrid for an S3 but not an A4? they are the same engine, maybe different spec but none the less based on the same thing.
One of the biggest draw backs of the A4 turbo is it's small size, in the K03 spec its a 150bhp unit and in the K03s spec it's 163 or 190bhp, same turbo just mapped differently, obviously twin intercoolers are used but mainly the tunning seperates these engines.
With a remap the 150bhp will get you 190bhp and the k03s will get you 220bhp-ish, good figures, but when the best hybrid on the market at the moment for the A4 claims 260-280bhp you have to ask where is the 50bhp that the others get? ( power claims are made on what the turbo could theorectically flow not actual figures )
So why is this? well for starters the best A4 hybrid is basically an S3/TT turbo in the A4 housings, when you add S3 injectors, maf and tuning you get a stage 1, Audi S3 engine in your AUDI A4 AVANT. Due to the layout and engine orientation it's impossible just to fit a K04 turbo and manifold from an S3 and make it work, it would be considerably cheaper so we are left with having to make the most out the K03 turbo on the A4.
Limiting factor on the K03 is definately the turbine housing, ideal at making boost quickly, not so good at moving large amounts of air, but with all this said it is still possible as shown recently with new manifolds and exhausts to get considerable power increases by just fitting some well choosen upgrades. Turn up the boost, turn up the power.
So where does all this fit in with my plan.
Well I am in the process of building a K03 turbo from an Audi A4, to it will be added the RS6 turbine as found in the new TFSI K04 and also the majority of hybrids for the S3 and to that add the 2280 compressor which is larger than the 2275 found in the S3 K04 turbo and has the added benefit of ETT. Extended tip technology. This combo, on paper and in a K04 turbo, is more than adequate for over 300Bhp with supporting mods.
Here's the Turbine housing machined out to take a K04 turbine from the S3 we di this initally to see if there was going to be enough metal left for it to take the larger RS6 turbine. The inducer on both these are the same so it was only the internal bore that needs to be machined futher to take the larger exducer the Rs6 turbine has. I plan to take as much as I can out from here to allow extra flow and also stop me from having to clip the turbine wheel to make it work...
At this point I just want to thank Kev ( aka Aragorn ) for his help so far and his pressure for me to keep this going :-)