E30 Zone

Current diff has no tag on it

Is there a way to work out what ratio it is?

Its not on a car

Most accurate way is to remove cover, count crown wheel teeth and divide by number of pinion teeth

Paint marks on the input flange and one of the output flanges.
Hold one output flange still, and turn the input flange ten turns while counting how many turns and part turn the other output does.
The ratio is half the number of turns the flange does. For example, if the output flange did 8 1/4 turns, then half of that is 4.125, which will be a 4.1 diff.
With a working LSD, you just let both output flanges turn together, and that will give the ratio directly.
Not as accurate as what Dan says, but close enough for you to match it to one of the available ratios.

Do each crown wheel have a different number of teeth?

Just trying to work out how I ll be able to see the pinion teeth!

Thanks guys am sure I ll work it out!