Just done a quick google using the term car engine modifications in Germany TUeV and it looks like any modifications from factory need to have a TUeV inspection, who then issue a certificate.
If you're stopped on the road by the Police with mods and without a TUeV certificate for ALL mods, which include wider or narrower tyres / rims then it's a fine.
I believe that the parts fitted usually have to have already had approval, not a problem if you're fitting a same make different engine, but may be a problem if your'e welding up brackets etc.
NOte TUV is the same as U.K Mot, TUeV seems to be the same as IVA (formerly SVA) in the U.K
Online information from TUV seems poor, but if it's anything like DVLA in the U.K, the info is there it's just badly indexed.
It looks like you'll need Individual Approval (same as U.K IVA) called Einzel Fahrzeugabnahme
Last edited by focusv8; Aug 10, 2020 at 09:47 AM.