GT - 1.6CC and SI - 1.8CC, you must know that the GT is the sports version. Well none of this 2 will be good in fuel. But if you are a long distance user then 1.8CC will give you some good figures. I owned a GT, and 97/99 manuals of 1.5CC Ti versions, GT was never good in fuel but was faster and was good in taking corners and in breaking others gave around 10/11 in city and 14-15 out station. Still owning the 99 model/Manual car but have to get moving now - Allion's are much better if you can afford them.