Maruti 800 and Maruti Alto both houses 800cc enginr but their bhp varies why

one is Japanese engine power other is korea power

power is different

Maruti 800 has 796cc 3 cylinder 4-stroke water cooled engine which means less bhp, but where as Maruti Alto has 796 cc gasoline engine with 3 cylinder, 4 valves per cylinder MPF l engine with 32bit ECM which means more bhp.
In general 4-stroke engines have less bhp & MPF l [Multi Point Fuel Injection] engines have better power output which means more bhp.
MPF l engines give better power output, fuel efficient, emissions performance, ability to accommodate alternative fuels, reliability etc.

It is because 800 has a carburettor and Alto has MPFI(multi point fuel injection) which not only increases the Bhp but also gives a better mileage. Other things are the same.