3.25 or 3.55
 

I have been reading about whivh gear set to go with, but im getting mixed results. I currently have the stock 2.75 in the back, which is great for highway use, however im mainly on traffic streets. I was thinking about a 3.55, but ive been told by somepeople that the engine will be spinning pretty high on the freeway. My trans is C4, out of a 79-81 mustang. It does have a B&M shiftkit, and a TCI torque converter. If any suggestions please help.

With a c-4 and 26" tires, I'm turning 3000 rpm at 70 mph with my C-4 and a3.25. If I was running a 3.55, I'd be running 3275 rpm's at 70mph. That's a little much for me, but it's something only you can decide. Hope this helps a little.

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'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

My 65 with 25 1/2" tires and a 3.50 gear turns 2850 rpm @ 60 mph. If the bulk of your driving is mainly in town the extra snap of the 3.55's is the way to go. Also, as Rev mentioned, overall tire diameter has a definite effect on your cruising rpm