BMW 318i Track Car What Diff?

[Rizzo]

Hi Folks

I am preparing a 318i M40 track car and was wondering if changing the diff is worth doing and what diff would people recommend?

The car is a 318i with the M40 engine pretty much standard but I might be tuning the engine at some point. Not decided yet.

Cheers,
Rizzo

[Brian28]

Hi, there aren't really any advantages to specific diff ratios, it will depend on the track. Lower ratio (higher number to one diff) will always give better accelleration, but the issue on tracks is more about having the car geared for corners, and this will be different track to track. What is a brilliant diff ratio for one track may be cack at the next track because on a couple of corners the ideal gear would be higher than 3rd, lower than 4th, mebbe a tighter corner is on the rev limit if taken in 2nd but no drive out if taken in 3rd etc. Just leave it standard and see how it goes I reckon.

Cheers
Brian

[Rizzo]

Thanks for your reply. All makes sense so I'll just leave it as is for the time being.

Cheers
Rizzo

[StreetSpec]

yeah man, worry more about getting an LSD for it.

i like my m42 with 3.9s, cos it gives a bit more headroom for corners on the circuit. but for tight/slow sections, my 4.45 was nuts.

[steerfromtherear]

Sorry to rape but what lsd's are available for 318is's, I presume 318i's are also included in this question?

[schuey]

I have a LSD on my 318 is,makes plenty of difference to my previous 318 is which had an open diff.
If anything 2nd gear is too short though.....