Diff ratio's

Post Mon Jan 31, 2005 3:15 am

Does anybody know what ratio's were used in the following?
320i
325i
325i sport
M3

Do the ratio's differ for early and late cars?

was the LSD only fitted to the sports and M3's?

Post Mon Jan 31, 2005 10:45 am

There is a list of diff ratios on the Unix Nerds BMW website. LSDs were fitted as standard on the 325iS and M3, and optional on other models.

Post Mon Jan 31, 2005 10:47 am

There are two sizes of diffs - small casing diff for the 316i/318i/318iS/320i and the large casing diff for 325i/M3. A large casing diff can fit the 318i - 320i models, but the small casing diff is too weak to handle the power of a 325i/M3.

Post Mon Jan 31, 2005 11:28 am

thanks for the help

Am I right in thinking that my 3.64 LSD is from a 323 then? as far As I was aware it was from an early 325i sport

Andy

Post Mon Jan 31, 2005 11:36 am

Need to be careful regarding diff ratios. If you go from a higher ratio diff to a lower ratio this will affect acceleration. There if a gearing calculator on the Unix Nerd BMW website that you can use to calculate the ratio of your existing diff. Take a sample rpm and corresponding mph reading in say 4th gear (gear ratio = 1.0) and you can confirm you rdiff ratio. If it is say a 4.10 ratio diff, then going to a 3.64 will not be good. Going from a 4.10 ratio to a 3.91 ratio diff is OK, you wouldn't notice too much difference.

Post Mon Jan 31, 2005 7:54 pm

anyone know what the unixnerds website is please.

Post Mon Jan 31, 2005 8:31 pm

billgatese30 wrote:anyone know what the unixnerds website is please.

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

M3 3.25
pre face lift sport 3.64
face lift sport 3.91
325 non-LSD 3.73

Post Mon Jan 31, 2005 8:58 pm

cheers dude. it looks like my speedo is over reading slightly, it's only noticable at motorway speeds where 75MPH reads as about 79/80MPH. not really a prob but i just thought i'd give it a quick check.

Post Mon Jan 31, 2005 9:42 pm

The speedos are designed/calibrated to overread slightly. That way nobody except the driver can be blamed if caught speeding.

I think it's possible to calibrate the speedo; I haven't checked the PCB since thinking of it, but the meter is connected through some kind of voltage divider/pullup. It may even be a potentiometer!

Post Tue Feb 01, 2005 12:13 am

There is a pot on the speedo PCB, but I've no idea what it's for.