s52 with 3.25lsd from e28

[E30_80Y]

RPM seem kinda high on the highway, i'm wondering if that's normal. I have a ZF tranny from e36 M3 and the 3.25 LSD differential from a 535i (e28). at around 70mph in fifth gear i'll be between 4k and 5k. what should i do to lower that? is the ration i need to change in the tranny or in the differential?

[jlevie]

Assuming OE sized tires at 70mph the engine speed should be right about 3250rpm for that transmission (1:1 5th gear) and differential ratio. Engine speed would be about 4250rpm with a 4.10. So something isn't right.

[E30_80Y]

sorry forgot to mention i have schrick cams too.

[phenryiv1]

To run the E28 3.25S, did you just have to swap the cover to an E30 cover, or did something else have to be swapped as well?

[jlevie]

sorry forgot to mention i have schrick cams too.

Cams make no difference in engine speed vs ground speed.

[E30_80Y]

To run the E28 3.25S, did you just have to swap the cover to an E30 cover, or did something else have to be swapped as well?

the previous owner of the diff had already done that for me, but i think you have to change the cover and the flanges that holds your axels.