I've been reading through the forums and S4wiki tuning guides and just getting started trying to write a tune. I am trying to get a head start on learning how this works by reading through the community tune threads and the s4wiki page while I wait for the spare ECU I ordered to arrive. My current challenge is figuring out the KRKTE and TVUB for the injectors in my car.

I have Bosch 0280155892 (from the TT225) in my AMB 1.8t (2003 A4).

I am pretty sure I have figured out KRKTE

Info from https://www.injectorplanet.com/collections/bosch-fuel-injectors/products/bosch-0280155892-volkswagen-06a906031j-1

That lists injector flow as 374.1 cc/min @ 3bar so I used https://deatschwerks.com/en-ca/pages/fuel-injector-calculator to get the flow for 4bar (431cc/min)
KRKTE = 50.2624*(1.781/4)/(431*0.684) ‎ = 0.075913
Does this seem like a good starting value? Stock is 0.1039 with the 263.8cc/min injectors (taken from the community stage 1 thread for 8E0909518AK)
If I do the same calculations for the stock injectors I wind up with 50.2624*(1.781/4)/(304*0.684) ‎ = 0.10763 which is close ish...

Now I can't find the TVUB values, and I can't seem to find any datasheets for these injectors, if anyone knows where I can find these please let me know.
Or maybe given I can't find a datasheet should I just try to get the TVUB values empirically via idle STFTs? I am just looking for a starting point given I can't flash the car yet.

Spare ECU arrived, bootmode flashed it with my original EEPROM and the STOCK file from the community thread modified with a KRKTE of 0.0758. The car starts and runs fine, I drove around the parking lot in 1st and 2nd, did not log but watching group 33 live fuel trim seemed to be between -8 and +8 percent.

Pulled TVUB from a TT225 file. Everything seems to run well, did a log, and to my (untrained) eye everything looks OK. Thanks for the help.