Hi cngF100.IIRC from previous threads,the engine must be purpose built for the CNG.
Compression should be in the neighborhood of 12 or 13-1.(If I am wrong here,someone PLEASE correct me).That is just a beginning.
I am sure that someone with more knowledge than I will be along to provide a more in depth
listing of how to build a proper CNG engine for long life and good economy.
Have fun.Good luck.And welcome to the I6 family.
"People never lie so much as after a hunt,during a war,or before an election".
Otto von Bismarck