its impossible for us to say how much you will gain, or if you will gain at all, because it depends how well the car cruises and idles now,
If it cruises at 9:1 then you can expect some mega fuel savings!
Closed loop will self calibrate the fuelling under certain driving conditions and allow a perfect cruise at lambda 1. its especially important on large injectors, where the ECU can struggle to have enough controlability or break points to map them to fine tolerances, and closed loop can "fill the gaps" so to speak.
Personally i wouldnt own a cossie without it being closed loop controlled. but thats my opinion, and the opinion of pretty much every car manufacturer who has made a car since 1992.
Fuel economy is only one of the reasons to fit closed loop, the plugs will last longer, the engine life will be increased, the oil will stay fresher and last longer,and you are doing your bit for the planet! all benifits of good fuelling.
Last edited by James @ M Developments.; 08-08-2011 at 04:06 PM.