in cng if u install intake with pipe then there will be no problem but if u install it directly on intak manifold(matlab throttle body) then its a very big problem and a wise man never installes it directly on throttle body becuz all of hot air direclty goes to the engine and hot air dosent have much oxygen in it ! if we install it with pipe then the intake is in a cooler region in the engine bay and the pipe controlls the air wen we use it in cng
personal xperience on my 5afe 86 corrola which is efi as u all know ! i installed it on the stock air filter pipe removed the air filter box only ! and there was 0% problem in cng ! same is the case with a frends integra