told ya,on petrol,free flow wil;l come handy,but on cng it will even decrease the performance..
reason is,petrol needs more air than cng..so wen petrol is on,it freely sucks air in so better combustion n better results but on cng,it takes the same amount of air as it was takin on petrol so performance graph goes down..
even cultus with company fitted cng has a plastic valve type things in way of air inlet which open n closes wen u use cng n petrol...
settings can b done to make ur car work on cng as with normal air filter was performin,but improvement is hard to get!