Originally Posted by BennyL
so, why do automatics have such high diff. ratios?
Because the automatic transmissions aren't geared the same as the 5 spd trannies, they're geared taller (numberically lower). On a 5spd e36, 5th gear is 1:1, on the automatic, the tallest gear is overdrive, so something like 0.8:1 for example (don't quote that number, i just used it as an example).
Also, 3.91 would be stupidly short for a street driven 5spd e46. Pretty much 3.45 is the shortest you'd every want to drive on the street with a 5spd. I currently have a 3.38, at 120km/h the engine is revving around 3500rpm. I don't think I'd want it any higher then that on the highway.