How much gas do you use a year ?
360 is 13% bigger than a 318 even if that translated into a 13% extra fuel cost that's like $130 a year on every $1000 spent. Does it matter that much ?
If it matters that much put about 13% less rear gear then you would run with 318 and should get around the same mpg but with a loss of performance.
I've never notice that much difference in intown mileage in older cars. 6 or 8, small or large displacement.
