Have rear differential ratio question and seek clarification on my convertible

[Bimmernut2]

Ok, I'm confused on the rear differential gear ratio on the ZHP w/automatic transmission. On this forum, in the FAQ, it states that the ZHP auto's came with a 3.64 differential per 'copy 'n past' below.
"Question: What is the final-drive ratio on ZHP-optioned cars?
Answer: The final-drive ratio for the manual transmission is 3.07, which is shorter than the 2.93 rear end that was available on the standard BMW E46 330. The final-drive ratio for the automatic transmission is 3.64, which is shorter than the 3.38 ratio found in standard E46 330 vehicles."

However, if I go to the 'other' forum here (3.07:1 Final drive ratio w/ manual trans instead of the standard 2.91:1. Convertibles retained the already installed 3.07 ratio.) it says that it has the 3.07:1 per below:

TEXT COURTESY of BMWNA
"3.07:1 Final drive ratio w/ manual trans instead of the standard 2.91:1. Convertibles retained the already installed 3.07 ratio."

And if I go to wikipedia (http://en.wikipedia.org/wiki/BMW_3_Series_(E46)#Performance_package_.28ZHP.29) it says the same as ZHPmafia

"The car also received a shorter final drive ratio which allows for faster acceleration; 3.07 vs. 2.93 for manuals and 3.64 vs. 3.38 for the automatic"

Ok, so there's a difference of information; which is correct?

If I check realoem.com (http://www.realoem.com/bmw/showparts.do?model=BW53&mospid=47707&btnr=33_1185&hg=33&fg=05) or Penskeparts.com (http://www.penskeparts.com/DiagramsMain.aspx?vid=47707&vin=pl51693&md=200504) and enter my vin# PL51693
They only call out the replacement "RMFD FINAL DRIVE" as 3.07:1 (manual) or 3.38:1 (for the auto)

Now I'm really confused. Short of jacking the car up & checking to see if there's a tag on the rear differential that calls out the ratio like my E34 535i......

Did the convertible get a different rear differential?
Can any of you gentleman help me out on this?

[alexandre]

RealOEM really has weird entries for the diff.

http://www.realoem.com/bmw/showparts.do?model=EV53&mospid=47725&btnr=33_1185&hg=33&fg=05

This is mine for an '03 manual sedan. PO upgraded to 3.46 anyway but it's weird that no 3.07 shows up lol.

[Hornung418]

It's simple: If you have an auto, it's got the 3.64. If you have a manual, you have a 3.07.

Sent from my GSIII, bitches.

[derbo]

If you look underneath (not even jacking up) you should see a heatsink on diff for the automatic convertibles.

http://www.e46fanatics.com/forum/attachment.php?attachmentid=314768

It should be like this. :)

[BRGcoopahS]

"Convertibles retained the already 3.07 ratio". Does this mean both the manual zhp verts and manual reg 330 verts have 3.07?

[az3579]

Yes. All ZHP's with a manual transmission regardless of body style got a 3.07 from the factory.

[terraphantm]

You can verify the ratio mathematically if you have any doubts.

[Bimmernut2]

RealOEM really has weird entries for the diff.

http://www.realoem.com/bmw/showparts.do?model=EV53&mospid=47725&btnr=33_1185&hg=33&fg=05

This is mine for an '03 manual sedan. PO upgraded to 3.46 anyway but it's weird that no 3.07 shows up lol.

@ alexandre...clicked your link to realoem & on that parts listing it does show For vehicles with "Performance Package Rmfd final drive @ 3.07 & also
For vehicles with Automatic transmission and Performance Package Rmfd final drive # 3.64"
Wonder why my specific vin# didn't? I went back to the 'select another vehicle' area & picked an E46 330Ci COUPE instead of convertible & it too shows the performance package. Strange....

[Bimmernut2]

@ Derek.....I'll try taking a pic to check it out but keep in mind, the convertible has a 'vibration absorber & bracket' right where you took your pic that doesn't allow me to get that clear of a shot. And if I can get a pic or visually check it out, will the "heat sink" presents or absence tell me what gear ratio it is? Is there a different design for each gear ratio?

[Bimmernut2]

You can verify the ratio mathematically if you have any doubts.

@Terrapnantm... how do you verify mathematically? Sounds interesting.

[danewilson77]

@Terrapnantm... how do you verify mathematically? Sounds interesting.

Just the ratio and the speed.

Sent from Williamsburg, VA USA

[derbo]

@ Derek.....I'll try taking a pic to check it out but keep in mind, the convertible has a 'vibration absorber & bracket' right where you took your pic that doesn't allow me to get that clear of a shot. And if I can get a pic or visually check it out, will the "heat sink" presents or absence tell me what gear ratio it is? Is there a different design for each gear ratio?

As long as your differential has not been modified, a heat sink will make the differential a 3.64.

The heat sink will bolt up to any e46 differential but it only came on 3.64 from the factory


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[Bimmernut2]

Derek....I jacked up the convertible & snapped a pic of the differential. NO HEAT SINK. So I guess I'll have to try to check RPM's at 60mph to determine what's in there. According to realoem.com it's listed as a 3.38. I found a site to calculate RPM's at any speed & for a 3.38:1 with auto overdrive @ .76, and 25" high rear tire, when doing 60mph it should show about 2071 rpm's
Here's a pic......

http://forum.e46fanatics.com/picture.php?albumid=5100&pictureid=27487

[midlandtech]

Talking of rear diffs is it possible to swap any diff in as long as it came from another e46 or are the ones from 330i's different? I have been looking at 3.46 but they are from cars with smaller displacement engines and am concerned that they will not be a direct replacement


~Steve
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[Hornung418]

You have to swap the input flange from your ZHP to the new one. Other than that, it's simple.

Sent from my GSIII, bitches.

[WOLFN8TR]

If you look underneath (not even jacking up) you should see a heatsink on diff.

http://www.e46fanatics.com/forum/attachment.php?attachmentid=314768

I have the exact diff on my 05 330 "Auto" Coupe.

[Bimmernut2]

I just checked realoem.com for an '05 330Ci coupe & it calls out the 3.64 differential for automatics. But when checking the convertibles from '03 to the last one built in '06, they ONLY show the 3.38 differential. Soooo, I am going to guess that Convertibles did not get it the 3.64 diff. For some reason they only put 3.38's in them. Just guessing here.

[derbo]

Talking of rear diffs is it possible to swap any diff in as long as it came from another e46 or are the ones from 330i's different? I have been looking at 3.46 but they are from cars with smaller displacement engines and am concerned that they will not be a direct replacement


~Steve
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You can get one from an x3 or a z4 as well.


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[alexandre]

^ or 530i... Basically anything that had the 3L.

For others (3.46 will probably come from 323i manual) you need to swap input flanges.

[terraphantm]

Have to be careful with the X3. I think some of them get the "small" case diffs which aren't rated for much torque. I remember Kpeng on e46fanatics blew up an X3 diff (and just replaced it with another... but I would try to get the medium case diff anyway)



I just checked realoem.com for an '05 330Ci coupe & it calls out the 3.64 differential for automatics. But when checking the convertibles from '03 to the last one built in '06, they ONLY show the 3.38 differential. Soooo, I am going to guess that Convertibles did not get it the 3.64 diff. For some reason they only put 3.38's in them. Just guessing here.

Have to remember the ETK is not necessarily accurate. It claims the 330i didn't get the 3.07 until March 2004, which is not true.

[terraphantm]

@Terrapnantm... how do you verify mathematically? Sounds interesting.

Vehicle speed = Engine RPM * Tire Diameter / (transmission gear ratio * diff ratio) --- convert any units as necessary.

Solving for diff ratio, you get

diff_ratio = RPM * circumference / (speed * trans_ratio) -- convert all

So say you're at 3500 RPM in 4th gear (auto) when going 70

diff_ratio = 3400 rev/min * 25pi inch/rev / (70mi/hr * 1056 (in*hr/min*mi) * 1)
diff_ratio = 3.61

So your actual results will vary a bit based on rounding and observational errors. But as long as you're reasonably close, the results should also be close. (Try using the digital tach and GPS). Also try to stay above 3000RPM since E46 autos don't lock their torque converters 'til about 3000 IIRC.

[Bimmernut2]

Vehicle speed = Engine RPM * Tire Diameter / (transmission gear ratio * diff ratio) --- convert any units as necessary.

Solving for diff ratio, you get

diff_ratio = RPM * circumference / (speed * trans_ratio) -- convert all

So say you're at 3500 RPM in 4th gear (auto) when going 70

diff_ratio = 3400 rev/min * 25pi inch/rev / (70mi/hr * 1056 (in*hr/min*mi) * 1)
diff_ratio = 3.61

So your actual results will vary a bit based on rounding and observational errors. But as long as you're reasonably close, the results should also be close. (Try using the digital tach and GPS). Also try to stay above 3000RPM since E46 autos don't lock their torque converters 'til about 3000 IIRC.

Ok I did it a little differently than the above math. I went to this site (http://www.csgnetwork.com/multirpmcalc.html)
and entered all the information for (3) possible ratio's: 3.07, 3.38 & 3.64; using a 25" dia tire and a .76 transmission drive in od/5th gear, the calculations came out as the following for a speed of 65mph:
3.07= 2038 rpm's
3.38= 2244 rpm's
3.64= 2417 rpm's
Then I set up my Android phone with the "Torque" app to show RPM's & MPH and hit the interstate and at a flat straight area running 65mph, I was very close to the 2244 rpm's. With a 200 rpm difference between the other (2) ratio's, I have to have the 3.38 ration rear differential as called out on REALOEM.com.
So, it appears that most if not all convertibles with the ZHP option, did NOT get the 3.64 differential, but the standard 3.38.
I'm wondering if they did it as an EPA gas mileage thing since the convertible is also heavier than the others. Whatever the reason, it is what it is.
I still love & enjoy the car, as it's my mountain touring vehicle and has plenty of power for this old man. Bragging rights don't mean much to me at my age. I did all the stupid stuff when I was young with my muscle cars back then. :>)
Let me know if you see anything that I did incorrectly

[johnrando]

Seems logical. You talking automatics, manuals or both?

[Bimmernut2]

Seems logical. You talking automatics, manuals or both?

Mine is an automatic with a build date of 4-19-05 w/ZHP option (PL1693). I can't say about the manuals. However, if I run this car PL16986 04/21/2005 coupe PsychoCemia, it shows the automatic WITH ZHP to have the 3.64 differential. I'm note sure if this coupe is automatic or manual.
If I run your car (PZ40412) it shows the same as mine, 3.38. your build date is 3-10-06, which is about a year later than mine.

[johnrando]

Wow, all this time I thought I had the 3.64, now I really want to know why they switched for the zhps. EDIT: Just checked, I don't see a heat sink.

[terraphantm]

So ZHP verts didn't get an upgraded diff. I can only assume they did that for EPA/Carb reasons

[WOLFN8TR]

Wow, all this time I thought I had the 3.64, now I really want to know why they switched for the zhps. EDIT: Just checked, I don't see a heat sink.

Next Mod??

[johnrando]

Next Mod??

lol

[CarbonZHP]

Resurrection. Im planning out my 5 speed swap and I was accounting for it being 3.64. Thankful I found this thread, info doesnt seem to be anywhere else

[ELCID86]

Really liking my 3.38. Not sure I'd want any lower for highway driving.


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"ZHP is a garbage option anyway- just some cosmetic upgrades with a different cam and diff to claw back some of the performance lost fitting those hideous and heavy wheels. Any 330 with a 3.46 diff will smoke a ZHP every time. The whole Mafia thing reeks of childish behavior." - an e46f member

[ELCID86]

I tried to grab some shots tonight of my 3.38 in 6th gear.

So far my MPG doing 75-80% highway driving has only dropped a about 1mpg.

23554

23555

23556

23557


---
"ZHP is a garbage option anyway- just some cosmetic upgrades with a different cam and diff to claw back some of the performance lost fitting those hideous and heavy wheels. Any 330 with a 3.46 diff will smoke a ZHP every time. The whole Mafia thing reeks of childish behavior." - an e46f member

[3ZHPGUY]

I tried to grab some shots tonight of my 3.38 in 6th gear.

So far my MPG doing 75-80% highway driving has only dropped a about 1mpg.

23554

23555

23556

23557


---
"ZHP is a garbage option anyway- just some cosmetic upgrades with a different cam and diff to claw back some of the performance lost fitting those hideous and heavy wheels. Any 330 with a 3.46 diff will smoke a ZHP every time. The whole Mafia thing reeks of childish behavior." - an e46f member

Looks good, it's got to be a blast in the low gears. I think it may be an issue for me at those highway revs. Interstates here have a suggested limit of 70 mph. To just roll with the traffic is 80-85 and I'm still getting passed like I'm doing 30, some days. [emoji12]


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[BMWCurves]

Nice, 3.38 is what I get if I were to swap for an LSD and a new final ratio. Not too aggressive, but enough of a change. What do our cars normally pull at 60, 70, and 80? I guess I could go test this out myself...

[az3579]

Nice, 3.38 is what I get if I were to swap for an LSD and a new final ratio. Not too aggressive, but enough of a change. What do our cars normally pull at 60, 70, and 80? I guess I could go test this out myself...
With stock 255/35-18 rear tires and everything else stock, manual ZHP:

60 - 2103 rpm
65 - 2278 rpm
70 - 2453 rpm
75 - 2629 rpm
80 - 2804 rpm

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[ELCID86]

With stock 255/35-18 rear tires and everything else stock, manual ZHP:

60 - 2103 rpm
65 - 2278 rpm
70 - 2453 rpm
75 - 2629 rpm
80 - 2804 rpm

Sent from my LG V10 on Tapatalk

Sounds about right.


---
"ZHP is a garbage option anyway- just some cosmetic upgrades with a different cam and diff to claw back some of the performance lost fitting those hideous and heavy wheels. Any 330 with a 3.46 diff will smoke a ZHP every time. The whole Mafia thing reeks of childish behavior." - an e46f member