Super Six fuel mileage

64Lucy said
I wanna say I have 2.73 in it now. i was considering a rear out of a 170 car. Its my understanding that the gears in them are 2.90ish

There you go guessing. You need to find out what gear you have. So far people here have been talking about how things work and you ain't listening.

Changing parts without knowing what is what. You're just wasting time and and money if you don't get the right combination of parts.