Differential decisions

[Dingg]

Hello. I'm planning on starting a s52 swap in the coming weeks. I'm going to be using a zf trans and was wondering what differential to go with. I'm between a 3.25 or a 3.46. Does anyone have experience with both? I'm wondering what highway cruising rpm's will be with the 3.46.

Thanks!

[TobyB]

Over 3k with the 3.46.

In a much heavier car, the m54b30 (similar hp/tq to s52) cruises well with a 2.91,
but 1st is tall at the light

3.15/3.25, methinks

t

[mtech325]

I have a 3.25 in my swap car with a ZF, and 80-85 mph on the freeway is around 3700 rpm with OE rolling diameter tires (205/55/15). If you're cruising closer to 70 mph, then a 3.25 should be plenty tolerable and still provide good acceleration.

[Codym42]

Any reason you wouldn't consider a 3.15? I have an m52/ZF with a 3.15 and it seems perfect to me.

[pazi88]

I think 3.46 is way too short ratio. 3.15 is perfect for NA engine. Longer one is then better if engine is boosted (I have 2.65 and it's really nice).

[Dingg]

Thank you guys for all the feedback. I was in between those 2 because I know the e36 M3 had a 3.23 and since I'm using the full M3 drive line, I thought the 3.46 might give a nice acceleration bump. But I was concerned about the highway cruising speed at that ratio. Hearing everyone's feedback though, I'm going to go with either the 3.15 or 3.25. Thank you again guys, I really do appreciate the input.