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01-05-2019, 09:10 PM | #1 |
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How can you tell what diff you have.
One of the upgrades listed on my car when I purchased it was that it came with a Dinan 4.10 differential. Is there a way to test out if that is indeed installed without opening it? The person that sold the car showed a picture of the receipt for the differential as proof but seeing as he also owned an E46 M3 I have always questioned which car it was actually installed in. I appreciate any help on this one.
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01-05-2019, 09:30 PM | #2 |
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Compare your rpm to a stock car in the same gear at the same road speed.
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01-05-2019, 09:40 PM | #3 |
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Compare RPM
Yeah....what he said.
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01-11-2019, 03:34 PM | #5 |
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Pretty simple really, use this calculator and plug in your values to check your RPM
http://www.bokchoys.com/differential...calculator.htm
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01-11-2019, 09:05 PM | #6 | |
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thanks, -E |
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01-11-2019, 09:34 PM | #7 |
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You use the rear tire specs in this calculator as they are the driven wheels.
The front tire measurement will be irrelevant for the purpose of this calculation. Let us know how you go please. I had 4.10 gears installed last year and this calculator worked out perfectly to double check everything.
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Last edited by ANILE8; 01-11-2019 at 11:55 PM.. |
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01-12-2019, 03:45 PM | #8 | |
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Rear Tires are 275 35 18 1st gear redline was about 34 MPH 2nd gear Redline was around 57 MPH as far as the last item of cruising speed of 70 MPH what gear should you be in for this I am assuming 5th? In 3rd gear I was doing 4701 RPMs In 4th gear I was doing 3809 RPMs In 5th gear I was doing 3244 RPMs I didnt check it in 6th One last measurement that I took was that I was in 3rd gear doing 30 miles an hour at 2500 RPM. ANILE8 thank you for the tool and please let me know if you concur on my findings. -E |
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01-12-2019, 04:08 PM | #9 |
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The Cruising Speed is measured in 6th gear which is the easiest way to check.
The way I checked it was to set my cruise control on whatever speed (in this case it was 63mph) in 6th gear and verify speed with phone GPS app. At this speed, my RPM was exactly 3K which equates to 4.10 gearing according to this calculator. You can redline in each gear if you choose but that is a much harder way of doing it. From your 1st and 2nd gear redline pulls, yes it looks like you have true 4.10 gears.
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01-12-2019, 04:13 PM | #10 |
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You can enter whatever cruising speed you want into the calculator to check.
I know the default is 70mph but you can just change this value to anything you want. Just remember to always check this speed in your highest gear which in our case is 6th.
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01-12-2019, 04:34 PM | #11 |
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you can calculate it easily from your data:
3244 in 5th gear. 5th gear has 1:1 ratio. With the 4,10 diff your wheels are turning 3244/1/4,10=791,22rpm Your tire circumference is 80,36", which means 788,45 revs/mile (1 mile is 63360") So in 1 min you travel 791,22/788,45 mile, so in 1 hour thats (791,22/788,45)*60=60,21mph if you have the 1:4,10 diff But you're writing you were doing 70. So 60.21/70*4,10=3.53 So calculated you have a 1:3,54 diff. Thats a heck more closer to the stock diff. (its not even inbetween the stock diff and the 4.10 diff) Variations in the calculation are your measured speed (did you use gps? or speedo), and tire wear (tyre wear can go up to 8mm or so, so 16mm in diameter) 4th gear is 1,23:1 and 3rd is 1,67:1 so you can now calculate it for those gears. But I think somethings fishy here, your rpm spacing is not correct I believe? Are you sure your data is correspondant to the gears you give? If you do the calculations with 4th and 3rd gear you get different values, which is, of course, impossible.
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Last edited by GuidoK; 01-12-2019 at 04:59 PM.. |
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01-13-2019, 07:22 AM | #12 | |
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01-13-2019, 10:05 AM | #13 | |
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Jack up rear of car. Place on stands. Chock front wheels Mark DS with marker of choice. Rotate wheel one revolution while counting rotations of DS. You will need to relate the last revolution of the DS to a percentage of a full revolution to determine accurately. However if you do indeed have a 4.10 final drive it will be obvious
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