hi guys just came back onto site.
See a lot of talk about this and several different views....
Yes you can chip/re-map DS4 takes the 1.6HDI up to about 135bhp (+20bhp) 280nm torque, takes the 2.0HDI to 200bhp (+40bhp near as damn it) and 410nm torque (+60nm). In the 2.0HDI these are 25% and 20% respectively not bad for £300 if you ask me.
The key here is the torque, you will never beat a 217bhp Golf GTI in a drag race, but some big sport cars do not produce 400+nm and therefore your ingear acceleration, need to change gear is less and that makes a better cruiser.
Also you can get performance and fuel economy simply because you have more power you change gear less, use less revs so economy improves - if you drive like a banshee nothing will improve fuel efficiency!!
You can use a chip system that overrides your ECU, and you pay for what you get. The cheaper ones around £60-£100 jus con engine into pushing in more fuel, and are not in tune with engine management system. The circa £300 chips are bespoke set-ups for your car and over ride ECU settings, but are easy to unplug and go back to normal. The danger is some will allow tuning car beyond safe paramenters which will make engine fail earlier.
The other option is a re-map (superchips) they reprogram original Citroen ECU (after backing up old spec) and therefore from insurance point of view no extra bits or tampering. Also because this re-map is on original ECU it compliments other ECU programming (Emyway etc) and is more in tune with car (works within cars maximum parameters). I have used both and prefare the re-map if possible.
My DS4 Sport 2.0HDI was chipped 2 years ago now got it to 197bhp 406nm, could have gone higher but strain on engine not worth it. Car can handle this easily, some slight more wheel spin (due to huge torque), but manageable - and allows you to burn of sill Seat Cupras and Golf GTIs especially in mid range - lovely