Rear end gears?

[snotrocket71]

So whats the deal with the overdrive? Does it make the car shifter smoother or just overall better with posi rears

simply put an overdrive trans (200-4r, 700r4, 4l60, etc.) lowers the cruise RPM where as a regular 3 speed auto (th350, th400, th200 etc.) does not because they have a 1 to 1 ratio final gear. for example a 200-4r has a .67 over drive which lowers cruise rpm's by 33%
i like this site http://www.ringpinion.com/Calc_RPM.aspx to help guide me with RPMs with different gears, tires and transmissions

 

[chevymalibu]

Im lost with the gears. I have a 2.73 gear 350 engine with trans. no o.d. I mostly drive my car in the street to work. On the freeway when I go to carshows. I want to add a posi. IF I put a 3.08 gear will be a big diffrence mfrom the 2.73. Or should I just leave the 2.73 and add a posi

 

[G-Body_Vet]

Im lost with the gears. I have a 2.73 gear 350 engine with trans. no o.d. I mostly drive my car in the street to work. On the freeway when I go to carshows. I want to add a posi. IF I put a 3.08 gear will be a big diffrence mfrom the 2.73. Or should I just leave the 2.73 and add a posi

Here's a calculator you can play with to figure out which tires, trans & rear gear works the best for you.
http://www.csgnetwork.com/multirpmcalc.html