HI there I have Nissan sunny 89 with 1000CC carby original engine its working fine its not much powerful just keeps the car going and on CNG I feel that it cant pull the weight of the car but there is no AC in it my work is in field and in summers I need chilled AC I spent last summer sweating all day, when I thought of putting AC in existing engine people advised me that your engine will collapse ,now I am thinking of swapping engine with used EFi engine I have two options 1: 1000 EFI engine and 2 : 13000 EFI engine I only want 3 things 1: mileage 2: chilled AC 3: get rid of CNG ,I don't want to waste my whole day in CNG queues I have seen the posts and I think here are many experienced people who have done experiments and so I will be much obliged if you could guide me which engine should I go for ??