Trying to decide on rear gear ratio.. I am building 355 400hp, m20 4speed and bu code 12 bolt rear. looking for suggestions on ring and pinion ratio. I want good bottom but also want good top speed. Im listening .....

 

If driving only around town, you'd be more than happy with 4.10's. Take it out on the highway once in a blue moon, 3.73's. But if doing combination driving, I'd go with 3.55's.

 

You stated you have a BU coded axle = 3.73:1
Wonder if original axle - could have been ordered singularly, or with an SS option - 4P on Trim Tag.
Might have radius rod? Round rod is early production up to Jan '67.

However, if looking for highway usage, 3.31:1 or 3.55:1.
Otherwise, leave it if BU is true.

 

Its not the original rear for car, I bought it in Pa. this week. its a 69 camaro rear from Z28. Someone put swapped the 3.37 out with 4.10. I do have the original 373 gear. I just plan to drive it and enjoy. the code is : Bu 1105G2 Casting is 3894860NF
E

 

This is the only important thought. Enjoy it.