Devide your dif poulie true your small poulie then you know your internal DR
So a E4RS has a 35 dif poulie and a 17 small poelie(same as the side poulies).
That gives a ratio of 2.0588......
No you have 73 main gear and 33 teeth pinion so 73/33x2.0588=4.554FDR
If i am not mistaken the E4FS has a internal ratio of 2 or at least mine has.
73/33x2=4.424
You can change your internal ratio by changing the dif poulie or the small poulie on your main drive and/or on the inside of your middle shaft.
Dif poulie are in 34 and 35 teeth and the small poulies are there in 17 and 18.
You can change the internal DR into 4 different types.

cheers Roy