its true that cng burns hotter and causes valve damage, but that differs by design from engine to engine. newer toyota 1.3 gets damaged by cng in no time but r18 runs fine. all suzuki engines including liana(if treated like a modern car), all varients of corolla, honda civic idsi and sx8, run fine on cng. the cars that give problems are some japanese imports(specific models), corolla 1.3 vvti and badly tuned carby vehicles.