Hey guys, i got a question, which is obvously why im here.

I got two diffs for my ba falcon, one currently on my car with 3.25 diff ratio, and the other one we pulled off a falcon, that i kept with 3.45, now i wanted to change either of the diffs to 3.9 maybe 3.7 and put a mini spool in it as im running N/A, but supposedly there are two different types of diffs for the falcons, like two different IDs, one has a max that goes upto 3.45, while the other can co beyond upto 3.7, 3.9, and even 4.11 which i won't go near.

so basically, what is the two ID's for a diff, and would it be cheaper to spend 1100 for a diff already made shipping included with LSD, or replace bearings if the diff i salvaged, plus gears and a mini spool??

For the BA/BF there are 2 diffs. Firstly, you have the M78 Diff that goes into the NA's (XT, XR6 etc).
You then also have the M86, which is the turbo and xr8 diff. Obviously the M86 is a lot stronger, and will take gears up too 4.11, where as the M78 will take up too 3.73 (anything after that, you've got to look at different gears from other diffs and using shims etc).

From the research I've done, I've been able to find out that the AU IRS diff is pretty much the exact same as the M78, except stronger (has 4 pinions instead of 2). They do fit the BA/BF apparently, don't take my word on it though!

This would lead you to believe that running an AU IRS diff would in actual fact be better than simply putting a LSD Centre and new gears into the BA/BF diff, and it's also about 200x easier to get gears for the AU diff also

Hope this helped. If any of this is wrong, feel free to correct me. This is just going off the research I found when I was searching a few months back.