What is the difference between a 4 cylinder nissan altima and a 4 cylinder infiniti g20?

My roommate and I got into an argument about my car wasting gas... Her response was mine doesnt waste so much and its a 4 cylinder too but of course i responded that my car was in fact bigger than hers... she replied that nooo that doesnt make a difference... so please will someone please give me a technical differnece so i can print out the answer and tape it to her freaking door!!!! thanks