wow what a thread. I came here to mention some things about the 4g63, but that not relevant anymore. Now let's talk about vag engines. I would have still preferred the 4g63 over the 1.8 as the engine and trans are stronger. Also easier to tune. (rebuilding and flipping 2g's and B5 A4's was how I made money in college) I just wanted to throw some info out
4g63:
crankwalk is blown out of propertion. If it didn't happen by 80k it won't happen.
98-99 had the upgraded thrust bearings
7 bolt stock reliable hp- ~500
6 bolt stock reliable hp- ~600
a bad tune will blow your motor at 300hp, so don't bubba it
$30 felpro composite HG and arp studs are good for 600hp
stock 6 bolt head bolts are good to 500hp
$250 delta regrind cams are AWESOME
93+ trans has a weak 3-4 hub that will let go around 450tq
91-92 trans has the big hub but any shop that's building the trans will upgrade that.
dsm auto's are stronger than manuals. they can run 10's. and rebuilds are cheaper.
there are shift kits for paddle shifter auto's that can run without a TCU
building a 2.3 7 bolt stroker is fairly cheap. Stay away from the 6 bolt stroker because 6 bolt 2.4 cranks are almost impossible to find. And once you go with aftermarket rods, the advantages of the 6 bolt are gone.
vw/audi: (I did mainly stock rebuilds on these)
stock 1.8T is good for 400hp
01a trans is good for 400hp
01e trans (S4 and A6) is good for 800hp
2.7T is good for 300/350 with just a flash. I've seen up to 320/380 on stock everything.
drive by wire engines have programmable ecu's. google "s4 tuning wiki" and check out the nefmoto forums for more info.
not as many clutch options as the 4g and they're expensive.
with any engine please run a wideband and oil pressure gauge