But with closed loop the fueling is matched to the airflow at the required ratio, so therefore you cant reduce the fueling otherwise it would run lean, so you would have to reduce the airflow to match.

My current car is Tax band 1, and is 109 g/km (£35 a year) but tax band 0 which is 100 g/km or less is Zero tax.

I was thinking that if it was straight forward and I wasn't over looking some complication then somebody could make a killing on designing this conversion for a given car..........

Perhaps a remap chip and an inlet reducer.

????