64 Impala with unknown gear ratio

Hey all, I just recently restored a 64 Impala with a 350 SBC, and a 350 Turbo transmission. The tire size I have is a 175/70R14. When going on the freeway I noticed I wasn’t able to go above 45 MPH without my trans screaming. Engine and transmission are both rebuilt. I’m not sure my gear ratio in the diff, but I was told that my tires are too small for my current diff and to get 205 Tires instead of 175. Would that really make a difference in my top speed?

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Originally posted on r/classiccars — View discussion