Previous corolla was great on CNG.
New corolla is a bit less in efficeny and pick then old shape on CNG.
I had owned 2006 corolla and keep her on CNG. it work great for me and sell it on 90,000 Km.
Now I have 2010 corolla, Installed CNG at 10,000 Km and now it has done 20,000 Km. Working fine on CNG but i have enjoyed 2006 corolla more as far as CNG is concern.