waldo... the story that auto bellett's (in australia anyway) had a 4.11 diff is just that.... a story.
the 3 original aussie delivered auto's i've seen had all had the normal 3.73.
as most original documentation came from japan, it says auto's had a 4.11, but not the ones we got. only explaination i can give is that our auto's were spec'ed differently when ordered?
having said this tho, i've seen 4.11 diffs around. i've only ever seen a handfull, so they are rare. as for why the cars i've seen them in actually had them .........
??there is a way to tell what the ratio on all bellett diffs are by looking at them. if u look at the housing, stamped into the rib that's cast into it near the oil fill plug, there's a series of numbers there.
they work like this:
early cars used a 3 digit code.
34 9 is a 3.778 ratio.
37 9 is a 4.111 ratio.
later cars used a 4 digit code.
41 11 is a 3.727 ratio.
41 10 is a 4.100 ratio.
the numbers actually relate to the number of teeth on the crown wheel and pinion. the first number (34, 37, 41) is the crown wheel, the second number (9, 10, 11) is the pinion. dividing the second number into the first number gives the ratio within.
as the later diffs had a more teeth on both the crown wheel and the pinion, they are slightly stronger than the early ones if you're pumping some decent power thru them. also, later diffs are more common than early ones too.
as a point of interest, i use a 3.73 in my race car. i've driven another car with a 4.1, and it really didn't feel that different to mine. also, we've had more success with getting gear ratio's better by using a better gearbox, but more so by playing around with tyre diameters. u'd be surprised what a difference a tyre that's 12mm smaller in diameter can do to acceleration!
hope this helps.
brett.