I am planning on running a olds 455 with 500hp and a overdrive transmission. I checked the code on the rear differential and it had (R2 00 20) stamped in the axle housing. Does any one know what rear gear this is and will it be ok for my engine and trans? I have not removed the cover to check what is stamped on the gear because i didn't have time to remove it. Any help will be appreciated.

Fred

 

Hi Fred
I don't know what year it is, so I can't say for sure. But my reference book shows the code R2 as being a 2.56 open, non-posi rear end for several different years.

If so those are great highway gears, but may be too tall for your overdrive. If your going with the 200R4 which has a .67 overdrive that would be a final drive ratio of 1.71 with that ratio. You might be better off with 3.42 to 3.91 gears. My memory isn't as good as it used to be, but I believe one of the guru's here suggested 4.33 as ideal with the 200R4 setup. That would give you a final ratio of 2.90

John

 

Yep, R2 is 2.56 open for the O-Type 12 bolt and the corporate 8.5" 10 bolt rears.