I think this is what your looking for http://forums.vwvortex.com/showthrea...-MKIII-vs-MKIV
The ABA intake is interesting. We ported one - tested with substantial increase in flow but it wasn't worth much power. We replotted the dyno charts so its easier to read here. http://www.scientificrabbit.com/node/27
I think the main issue with the ABA intake is the small diameter at the joint between upper and lower sections. The mk4 lower has much better taper and inside diameter for the sharp turn. I do think in the test pages we list the plenum volumes are different also. Most OEM plenums are to small anyway.
Would be interesting to see a ABA upper mated to the MK4 lower, but they don;t align well/at all. Think I have a picture of them next to each other if you need it.
Would be much easier to take a mk4 intake can cut the plenum and flip the TB to the side you want it on.