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This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 03-12-2014, 01:38 AM   #1
Archbid
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3.38 Differential for Sport 330ci

My differential is hemorrhaging oil at this point - 330ci convertible 104k.

I like the idea of replacing it with a 3.38, which seems reasonably available on eBay. However, I have the sport package, and I want to make certain I am not opening up a can of worms.

Any issues I am not paying attention to? I have read the posts on the varying effects of different gear ratios, so I am not looking for more info on what the effect will be on performance, just any feedback on whether it is going to fit!
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Old 03-12-2014, 01:58 AM   #2
love2drive330CI
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I believe you already have a 3.38 if that is what you are trying to confirm?
Here is a good listing from bokchoys.com

http://www.bokchoys.com/differential/GearRatios.htm
Hope this helps...sure more experienced will chime in soon.
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Old 03-12-2014, 08:31 AM   #3
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Wow. That is a table! I have a manual transmission, so it is a 3.07. But I was really just checking that if I buy a 3.38 from eBay it will work in my 5-speed.
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Old 03-12-2014, 08:52 AM   #4
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Careful with the 3.38. You may end up at a high RPM on the interstate.

It SHOULD work. The input and output flanges should match up with everything on your car if you purchase one from a 330. I purchased a 3.38 to replace my 3.38 that died (automatic) and got a good one for <$300.

According to my calculator, you'll be 3218 RPM@70 mph and 3677@80 mph with the 3.38 vs 2923 RPM and 3340 RPM respectively for the 3.07. Seems okay to me.
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Old 03-12-2014, 09:27 AM   #5
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That's a clever spreadsheet, WDE. I do a ton of highway driving, so I'm curious if there would be any noteworthy increase in fuel economy if I switch from a 3.38 to a 3.07.
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Old 03-12-2014, 09:48 AM   #6
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Of course you'd get better mileage. Like adding an overdrive gear.
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Old 03-12-2014, 10:45 AM   #7
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Originally Posted by HLG600 View Post
That's a clever spreadsheet, WDE. I do a ton of highway driving, so I'm curious if there would be any noteworthy increase in fuel economy if I switch from a 3.38 to a 3.07.
6speed manual or 5speed auto? if the latter, i wouldnīt recommend the swap as the auto is almost diesel-like shame on bmw for that setup.
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Old 03-12-2014, 10:50 AM   #8
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6speed manual or 5speed auto? if the latter, i wouldnīt recommend the swap as the auto is almost diesel-like shame on bmw for that setup.

No it's not. 3000 rpm at 80 mph is fine.


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Old 03-12-2014, 11:01 AM   #9
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Of course you'd get better mileage. Like adding an overdrive gear.
Better yes, but the question is anything noteworthy. I'd do it for a 2-3 mpg gain. I have an AT.
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Old 03-12-2014, 11:17 AM   #10
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I have a 3.38. I had to swap output flanges, but that's easy. RPM's are fine on the highway. I was worried which is why I chose it over the 3.46 but I'm still getting 22-23mpg on avg.

Edit: I have a 6spd, so...yeah.
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Old 03-12-2014, 12:20 PM   #11
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Quote:
Originally Posted by Sedan Hussein View Post
I have a 3.38. I had to swap output flanges, but that's easy. RPM's are fine on the highway. I was worried which is why I chose it over the 3.46 but I'm still getting 22-23mpg on avg.

Edit: I have a 6spd, so...yeah.
If you have a 6-speed then that completely changes everything you just said. The 5-speed doesn't have an over-drive gear. Your car in 5th gear is the same as the 5-speed in 5th gear - 1:1. Drive your car in 5th gear on the highway and you'll see exactly what it would be like if he were to put the 3.38's in his car.



But the reality is people run 3.46's in their 5-speeds and can deal with some top-speed loss and slightly high revs on the highway. You'll be fine with 3.38's.
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Old 03-12-2014, 01:20 PM   #12
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No it's not. 3000 rpm at 80 mph is fine.


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Actually i donīt know what you are talking about and i bet you havenīt even driven a 330iA, thats why you talking so strange things.

let me help you by clearifying with pics:

This is the actual situation from HLG600



and this is what would happen if he chooses the 1:3.07 diff:



really affordable, isnīt it?!

keep in mind, that the torque converter is even more working the longer the ratio is. so you wonīt save exactly nothing while changing the gear ratio into longer ratios at an automatic transmission. keep in mind, that the use of a torque converter rises your fuel consumption.

if you want to lower your fuel consumption at an AT 46, you have to shorten the gear ratio!

why am i so shure about this behaviour? because i did it! i lowered the ratio with a 3.91 diff and the fuel consumption lowered by 0.5-1L/100km!

if you still believe in lowered fuel consumption when raising the ratio: keep looking for the fuel consumption maps from the m54b30 engine and have a look what really happens when you raise it. the revvs will be lowered, but you need more opening angle of the throttle and so your raising on the y-axis of that map! -> higher fuel consumption.
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Old 03-12-2014, 01:30 PM   #13
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He has a 5-speed manual. No torque converter.

Archbid, please put in your first post that you have a 5-speed manual. there's no reason why we should have to scour posts to find that vital piece of info when you should have put it there in the first place.

Last edited by Cavi Mike; 03-12-2014 at 01:33 PM.
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Old 03-12-2014, 02:27 PM   #14
WDE46
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3.38 Differential for Sport 330ci

Quote:
Originally Posted by daniel_f. View Post
Actually i donīt know what you are talking about and i bet you havenīt even driven a 330iA, thats why you talking so strange things.

let me help you by clearifying with pics:

This is the actual situation from HLG600



and this is what would happen if he chooses the 1:3.07 diff:



really affordable, isnīt it?!

keep in mind, that the torque converter is even more working the longer the ratio is. so you wonīt save exactly nothing while changing the gear ratio into longer ratios at an automatic transmission. keep in mind, that the use of a torque converter rises your fuel consumption.

if you want to lower your fuel consumption at an AT 46, you have to shorten the gear ratio!

why am i so shure about this behaviour? because i did it! i lowered the ratio with a 3.91 diff and the fuel consumption lowered by 0.5-1L/100km!

if you still believe in lowered fuel consumption when raising the ratio: keep looking for the fuel consumption maps from the m54b30 engine and have a look what really happens when you raise it. the revvs will be lowered, but you need more opening angle of the throttle and so your raising on the y-axis of that map! -> higher fuel consumption.
First, I own an automatic you jackass.

Second, I never made any claims or suggestions about fuel consumption. So address the right people.

Third, you raised the ratio with a 3.91. You did not lower it. Keep your definitions straight.

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Old 03-12-2014, 02:34 PM   #15
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It's unclear what is trying to be claimed here. Yes, a torque converter increases fuel economy, but since I'm not discussing swapping in a MT, that is moot.

Daniel, a more aggressive gear ratio will raise engine speed on the highway, so I'm not sure how you're claiming it will increase fuel economy.
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Old 03-12-2014, 02:36 PM   #16
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Quote:
Originally Posted by WDE46 View Post
First, I own an automatic you jackass.

Second, I never made any claims or suggestions about fuel consumption. So address the right people.
I don't know why that's so funny but I can't stop laughing

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Old 03-12-2014, 02:38 PM   #17
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OP has a 5-speed MANUAL. Not sure where this talk of automatics is coming from.

http://forum.e46fanatics.com/showpos...27&postcount=3


Can a mod maybe update the first post of this thread with that info? This thread is getting very confusing.

Last edited by Cavi Mike; 03-12-2014 at 02:38 PM.
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Old 03-12-2014, 02:42 PM   #18
Knight
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Originally Posted by Cavi Mike View Post
OP has a 5-speed MANUAL. Not sure where this talk of automatics is coming from.

http://forum.e46fanatics.com/showpos...27&postcount=3


Can a mod maybe update the first post of this thread with that info? This thread is getting very confusing.
I'm responsible for that. As a side comment, I was asking about an estimated effect on fuel economy switching an 3.38 diff to a 3.07 one in my AT.
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Old 03-12-2014, 03:15 PM   #19
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It's unclear what is trying to be claimed here. Yes, a torque converter increases fuel economy, but since I'm not discussing swapping in a MT, that is moot.

Daniel, a more aggressive gear ratio will raise engine speed on the highway, so I'm not sure how you're claiming it will increase fuel economy.

From what I know of engines and power and torque, etc, I can speculate as to why fuel consumption would improve or worsen for either setup. So the only real way to see would be to measure it. One thing that is constant is the amount of force that must be applied to the road through the rear wheels no matter what diff you have.


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Old 03-12-2014, 04:23 PM   #20
Knight
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Originally Posted by WDE46 View Post
From what I know of engines and power and torque, etc, I can speculate as to why fuel consumption would improve or worsen for either setup. So the only real way to see would be to measure it. One thing that is constant is the amount of force that must be applied to the road through the rear wheels no matter what diff you have.
Let's take two of the same car, going 80 mph. One is at 3000 rpm while the other is at 2500 rpm. If the only delta is the engine speed, would the car at a lower engine speed not achieve a better fuel efficiency in most cases?

There are plenty of documented cases where switching to a less aggressive gear ratio increased fuel economy, and vice a versa. I'm just trying to understand in more detail why Daniel is claiming the inverse.
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