Hi all I have a 177bhp n47 e90 the original diff has play and and needs replacing Ive been searching the net and stumbled across diff ratios for short shifting and better acceleration my original diff has a ratio of 2.56 ive been looking to upgrade to a 3.46 or what ever the highest ratio i can that is compatible with my car also does anyone have the information on what the speed comparison will be through out the gears i understand that a higher ratio i will lose top speed but im attracted to faster acceleration 

 

thanks dan

Morning Dan

Is the play in the Diff or drive shafts ? I may be wrong but I thought your car came with 2.56 or 3.15 diff depending on Transmission. The bigger engine models 330i or M3 are 3.15 or 3.08 (check I am an old bloke)

I would check the whole drive train for wear slack in all prop-shaft joints and drive shafts. If more acceleration is your goal then a simple ECU tune would push power to about 210hp with a good increase in torque. How ever if your getting there quicker make sure you can stop faster to, so don't forget brakes and suspension.

Dave

Hi mate I jacked up the D/S/R end of the car yesterday with the wheel removed I rotated the disc back an forth and I could hear and feel the knocking through the drive axel. The drive axel (from wheel to diff) didn't appear to move instantaneously it seems there is slight play but its enough to cause a knock throughout the entire car when I pull off in 1st gear from being stationary and its the same for reverse as well so after I noticed that I decided to check the prop shaft and rotate that and there is also a knocking there when I use the same method that I applied to the disc.

Hi Dan

I take it there is oil in the Diff ? When you rotate the prop is there play or movement in the Rubber Doughnuts that connect each end they are a known cause of issues as they crack with age and use/abuse 🤣 Plus they are considerably cheaper than a diff. With the drive shafts check each end for loose bolts

Dave

thank you mate ill give it a look over and get back to ou with an update