efi and mfi are different

only ports are diferent though it wil bolt on just the same

the valves between a frst,s2,xr etc are teh same, its only the s1 that had sodium filled valves so i was told

but the black top cfi engines 1.4cvh are different on teh combustion chanbers on teh heads and different valves but ive heard these are the best heads to use when going efi but need to have a lot of machining doen for it to work