engine size dont matter if correct kit is installed, the normal kit imported here is mostly for cars under 100hp (lendi tn1 model). civic is 140 hp, it needs better cng kit, sequential one is even better, but then again it'll cost atleast 1-1.5 lac + 1.5 lac drop in price of car, with availability of cng declining day by day, amount cannot be recovered. if cng was installed before 2010 its a whole different scenario then.