You won't get 400whp from a hybrid K04 normally fitted to S3's....
You will need a GT30 or GT35 to get into that region of whp...
Realistically, a 1.8t will do 600+ hp with the right turbo strapped to it but obviously the rest of the engine needs to be built to take that level of hp...
If you are doing this a bit at a time then I would suggest getting the engine sorted first...
As mentioned though... the TFSI K04 shows promise... 370hp (at the flywheel, we aren't american) can be had with the right mods and its yet to be seen what a hybrid is capable of but could be in the 400hp region...
Any engine going for this level of power should be sound, have rods and arguably if heading towards 400hp on a larger framed turbo valve train too...
Biggest issue I have seen lately is worn engines... anything over 100k miles seems to vary massively... have seen sound high mileage engines like Gops make decent power but others are just too tired requiring a full rebuild..
You won't get power by bolting a GT35 onto a tired engine...
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