M40i AC Schnitzer engine upgrade.

[Pondy]

Also, will it be noticeable if you take the car back into BMW.?

Not unless they look. If it's a warranty claim they will look and they will refuse the claim (unless it's a warranted BMW remap). BUT.......many software 'flashes' can be removed then re-installed by the owner multiple times. There are many opinions whether a dealer can tell if the ecu has been 'tampered with' at all.
I have heard of a lot of people having their remaps 'wiped' by dealers by accident, especially if a software update is carried out.

I know that Ford (and other manufacturers) have 'locked' their ECUs since mid 2024 to prevent third party remaps. Tuners are desperately trying to find ways of 'unlocking' them as it's affecting their businesses.

 

[DPG]

Yeah that’s a s**t loads of cash for a tuning box

I thought the ABT upgrade on my TT was expensive but at least that was a new ECU

 

[craig3.2]

Maybe he’s forgotten as it’s all but impossible to use more than a stock car has….

…..and he spunked a s**t load more than £4k at the thing….

I was thinking the same.....saying "isn't 340bhp enough" and "4k" for extra power.
Bit of a stupid thing to say when you've tuned your own z4 to 500bhp or whatever and spent £10s of thousands doing so.
Mmm,bit of irony there. Or just plain old double standards bs from mr google,lol