What is my diff ratio?

[Ahheck01]

I was told the car has a 3.15 LSD from a 325.

at 80mph, I'm at 3,500rpm, at 70mph, I'm at 3000rpm in 5th gear (transmission was swapped from an M3).

Can you verify I have a 3.15, and back that up with some sort of online documentation? Thanks!

-Evan

[Spahrman5]

Manual 325s came with open and limited slip 3.15s. You can check the tag that is bolted to the diff cover to make sure. If is starts with an 'S' you have limited slip. The ratio is on the tag as well.

[Spahrman5]

btw, your rpms and speed sound exacly like my car with the 3.15. Now just make sure its a limited slip

[bloxsom]

you have a 3.15 same as me.
i am at 3,000 rmp at 70

[Ahheck01]

Guys, there is no doubt in my mind I have a limited slip :devillook

I just want to confirm my ratio. Thanks guys.

[bene36e39]

Speed & RPM can be affected simply by your tire size. The only sure ways to check if you have a real LSD are:

1) check for the big white "S" logo on the diff, it will be hard since it's facing up when installed (can be painted fake).

2) check for a small metal tag bolted in the rear of the diff, it should say s3.23 (can be added fake).

3) jack up your car in the rear, spin one wheel, if the other goes the SAME dirrection, it is for a LSD (can not be faked in any way).

4) please stop judging it by using RPM & Speed... because you can have any ratio you want but it can still be an open diff

[Ahheck01]

Speed & RPM can be affected simply by your tire size. The only sure ways to check if you have a real LSD are:

1) check for the big white "S" logo on the diff, it will be hard since it's facing up when installed (can be painted fake).

2) check for a small metal tag bolted in the rear of the diff, it should say s3.23 (can be added fake).

3) jack up your car in the rear, spin one wheel, if the other goes the SAME dirrection, it is for a LSD (can not be faked in any way).

4) please stop judging it by using RPM & Speed... because you can have any ratio you want but it can still be an open diff
Dude, you're missing the point. I know I have an LSD as a fact. I've done number three. All I'm trying to figure out is my ratio - if it's a 3.15.

[bene36e39]

Sent you an email with a professional gear ratio convesion chart, input your tire size in inches (it will be around 24" or 25" for 17" or 18" rims), enter your "suspected ratio", ignore the 6th gear (it's for euro tranny). Then you can be sure.

[bene36e39]

Dude, you're missing the point. I know I have an LSD as a fact. I've done number three. All I'm trying to figure out is my ratio - if it's a 3.15.

How about number 2? The tag has its part number starting with s3.15 xxxx. Simple as that.

Anyways, sent u a conversion chart already.

[auto3251]

just look at the tag, it takes 5minutes.