Finding out differential mounted in car? - The Unofficial BMW M5 Messageboard (m5board.com)

derheilige82 · 8th May 2007, 07:50

So, in my neverending quest to determine what if any mods the previous owner did to the car, I'm now miffed as to what diff I have in the car.

My understanding from previous posts is this:

6th gear 3000rpms: 3.15=88mph, 3.45=80mph

So tonight here are my results:

Ambient T: 8.0C (46.4F)
Altitude: 100m (328.1ft) AMSL
Gear: 6
RPM: 3,000
Fuel: 17.5L (4.63gal)
Speed: 160kph (99.4mph) ????

I do have a Dinan CAI, but all else is stock, wheels, software, everything....any ideas??

Thanks

qwyjibo · 8th May 2007, 08:03

why not actually look at the differential and see what it's labeled? it's going to be a lot easier and more accurate than what you're trying to do.

rdm190 · 8th May 2007, 15:01

If you are really stumped put the rear up on stands, spin the wheels (by hand). Count the number of driveshaft rotations per one wheel rotation. Post back and I am sure we can figure it out.

Looking at the diff for plates/numbers is a good idea too

derheilige82 · 10th May 2007, 09:03

I know but this completely throws a wrench into the spreadsheet that was posted once by a member on this site that helped calculate all the ratios...I was hoping someone would mention that...

also...moderator...please stop editing my titles...

mottati · 10th May 2007, 19:32

do you have stock tire sizes? Maybe you can pm member gsfent, he put a 2.65 diff in his car, maybe he can chime in on the speed at 3k in 6th.

Shardul · 10th May 2007, 22:54

If you can see the barcode lable on the differential the last 3 number are the gear ratio.

ard · 10th May 2007, 23:33

Quote:

Originally Posted by derheilige82

also...moderator...please stop editing my titles...

Wasn't me, but mods will edit titles when they aren't English or don't convey the subject. It helps when folks do a search in the future.

"Help identifying what differential ratio I have" or
"Identifying differential ratio when mounted in car" or
"what differential do I have"
are arguably better than the current title... currently there seems to be a word missing for it to make sense.

But hey- I'm not gonna edit it!

A

gsfent · 11th May 2007, 00:08

Quote:

Originally Posted by mottati

do you have stock tire sizes? Maybe you can pm member gsfent, he put a 2.65 diff in his car, maybe he can chime in on the speed at 3k in 6th.

Haven't been there recently

, but 3k in 6th with a 2.65 is about 104 indicated. 2k is 72 indicated.
Regards,
Jerry

derheilige82 · 11th May 2007, 02:30

Yah I have stock everything...I'll see if I can check out the barcode this weekend...so for the sake of argument im at 100mph at 3k in 6th...so if we take into account the "accuracy" of the cluster we've all grown to love...it's possible it's a 2.65 diff....since neither the 3.45 nor the 3.15 are anywhere close to these speed/gear/rpm levels even if you assume some innacuracy of 4mph in this case...

Who makes a 2.65 and why would you install this versus a 3.15/3.45?

ard · 11th May 2007, 02:44

Quote:

Originally Posted by derheilige82

Yah I have stock everything...I'll see if I can check out the barcode this weekend...so for the sake of argument im at 100mph at 3k in 6th...so if we take into account the "accuracy" of the cluster we've all grown to love...it's possible it's a 2.65 diff....since neither the 3.45 nor the 3.15 are anywhere close to these speed/gear/rpm levels even if you assume some innacuracy of 4mph in this case...

Who makes a 2.65 and why would you install this versus a 3.15/3.45?

To get an accurate speed, you can use the GPS determined average speed: go to the display for Average speed and hit reset- the very next update will be your speed. As long as you are pretty much constant it will be accurate.

A