Hi guys, driving around in my late dad's 2004 x3, loving it, not getting rid, realise it's got too much emotional memories. Wanting to make it quicker up to 60ish. Don't do too many miles and it's a 2.5i

Hi Richard

Welcome to the Forum

With normally aspirated engines an ECU tune will not give huge power gains from what I have read your 2.5i will be around 180/190hp stock a good ECU tune should see 215/220hp 

First google ECU tuners in your area and talk to a few see what they think outside that it is conventional tuning Headwork, injectors, Throttle body, exhaust, inlet etc a friend of one of our sons built a 1 series Drift car 2.5i based had around 350hp when he finished

I guess it's the Carol Shelby question, Speed cost money young man how fast can you afford to go 🤣

Enjoy your Beemer

Dave

Hi Richard. 
welcome to the forum.

as greydog said, it depends on what you are trying to achieve. 
my old company motto was ‘nothing is impossible, it just costs a lot more’

a remap and air filter/ exhaust will show a little gain, a low pressure turbo unit will show a fair gain. … a full engine swap will be big gains… but then it’s big brakes and chassis mods too.

give us an idea of budget and dreams are and we can go from there! 😜