How do i calculate change in RPM from one ratio to another?

[Jason]

specifically 3.46 to 3.91

[Jason]

specifically 3.46 to 3.91

[632 Regal]

specifically 3.46 to 3.91

[Martin in Bellevue]

I replaced the open 3.46 with a limited slip 3.64 this spring. It seems to be great. First gear is useable around town.

I think Robin has a 3.91 in his 535 5 speed. The previous owner converted it to a 5 speed leaving the differential.

specifically 3.46 to 3.91

[Robin-535im]

I've got the 3.91 in my blk/tan 1990 535iM, it was converted from an automatic like Martin said.

Did you see the post from Jeff N asking about diff ratios? Some good input from the board on what it's like.

If you look at the chart, 1st w/3.46 is pretty close to 2nd w/3.91.

The top line of each gear is 3.46, bottom is 3.91

EDIT: I made a mistake in the calculation... let me get it right and I'll repost.

[Jason]

Based on Jeff's formula im looking at 3400 rpm... is that accurate?

[Jason]

Now why didn't i think of that? thanks

[Jason]

I replaced the open 3.46 with a limited slip 3.64 this spring. It seems to be great. First gear is useable around town.

I think Robin has a 3.91 in his 535 5 speed. The previous owner converted it to a 5 speed leaving the differential.

[535ise]

Try this ratio calculator

http://www.unixnerd.demon.co.uk/revs.html

Andy

[Robin-535im]

Based on Jeff's formula im looking at 3400 rpm... is that accurate?

I couldn't say that one ratio is better or worse, it just places your gears in different ranges. I personally liked 3rd with the 3.46 better because you could pass on the freeway at the high end of 3rd. Now I usually take people in 4th, and the car's not yet in the max power place at the beginning of the pass. However, I really like 2nd w/3.91 around town because you can pull real hard through 2nd yet not really be speeding at the end.