Hi,

I am building a Lotus 7 type car using the complete rear-end I picked today from a BMW 320A at the wrecking yard. It is a disc brake rear-end and is Australian delivery car.

What is the diff ratio? And would it be LSD (hopefully)? I can't remember it is was an automatic or manual, but if somebody provides both info I can go back and check the car.

Thanks.

What is the

never heard of a 320a, but if it's got disc brakes in the rear it's probably a 3.91 LSD

Only 323s are supposed to have rear disk brakes, so there's something not right about that car. We don't even know if its a 320 4 cylinder or a 320 6 cylinder. It could be any of several ratios, 323 has 3.4something, theres a 3.64 and a 3.91 for the 4 cyl cars (and more). There should be a metal tag on one of the bolts that tells the ratio, or just count the turns and try to figure it out. If its a LSD it will have a S on that tag and if the paint is still on it theres an S painted on the side. You can easily figure that out by turning it though. There are several ring and pinions from other cars that you can install in it too if you decide you need a different ratio. (the diffs aren't the same but the ring and pinions are interchangeable).

Thanks for all the information.

The car is definitely a 320, and it is a 4 cyclinder, and it has disk brake rear end.

Through my web searches I too could not find a 320 E21 that came with disk on the rear.

We counted the turns and came up to about 3.8ish so maybe it is the 3.91 with LSD mentioned?

The diff does not have any tags or markings.

if you can turn the wheels in opposite directions by hand it's an open diff, if not its an lsd

Open it and count the teeth on the ring gear and the smaller gear and divide the numbers for the ratio. If it's a LSD you won't see the spider gears.

mine has no tag on it also but the owners manual says its a 3.91 open and since the car only has 160k miles and the other owners were older retiring guys i think its original

Thanks to everybody for your help, and not ridiculing me for using BMW parts on my lotus 7 ;-)

This is our second lotus 7 build -> First one was just finished and registered in a total of 12 months (from scratch to rego). It is awesome to drive, so with the new build we are trying to improve on our first one.

you can turn the input flange and count how many turns it makes compared to one full turn of the output flange. that will give you a very close number on the ratio.

the lotus super 7 cars are very cool. some guy local to me have had one or two and run them at the autocross every month. i wish i could drive it once because it looks so cool

Was the body an e21? Because I used to watch the Austrilian World cup championships and they raced 320 e36s......