sorry i think i didnt get ur question right...were u asking that y petrol gives more performance then cng?or u asked that ur car performs better on cng then on petrol...if the 2nd one,then ur car is tuned to run on cng.some times this happens...cars do better on cng then on petrol...
if ur question was the 1st one,then ,well,petrol burns much faster then cng...thats y it produces much more energy nd hence gives better performance...