With modified map durations the stock 140bhp Bosch injectors will flow more than the 170bhp Siemens injectors which is enough for 260 or thereabouts Bhp. Some folk up north claim 300 Bhp on stock nozzles albeit with crazy EGT figures and some bandaid mods thrown in: water meth injection and such !
I would not bother with a bb43 hybrid if I was to modify one of these ( mater of fact I have one modded already), whilst ok size wise for a daily driver, the shaft is weak on these and the EGT are high. I would start with a better turbo from garret stable altogether. A gtb2056vk is a better alternative but at that power level a gtb1749vk willso just as well. I am keeping tabs on a friends a4. It used to be 170bhp engine but we rebuilt it with lower CR pistons and it has Bosio race injector nozzles which- to this day- we cannot find a diesel specialist able to get them to flow properly ! With a FMIC, hybrid gtb2265vklr ball bearing turbo and a bunch of goodies the car put over 350 Bhp but it kept melting the VNT tips due to high EGT. It's now runs a safe 290-300 Bhp and it holds together although not without the odd issue every once In a while ! I would look at a 6 cyl engine for silly power, the rotating cycles means the pistons have more time to cool and make power and torque in a more liniar fashion which is far safer for the driveline ! The Quattro is mandatory, you just cannot put that much power on the road reliably, my mates runs 19" rs4 wheels and sticky toyo proxes tyres and fancy Bilstein pps9 coilovers and whilst the grip is here, one gets to the limits of mechanical grip a 2 WD offers pretty quickly ! We nearly ended into a ditch many a time before whilst taking power/boost logs !