**3.91 Diff Swap: Everything you need to know!!!**

Originally Posted by T330

chow mein

I'm a fan of pork fried rice

Had to bump this up, this is going to help me a lot with my 3.64 swap from a z4 may also have to change the drive shaft as well for my 330.

Originally Posted by msuka

may also have to change the drive shaft as well for my 330.

Don't worry about it, it took me all of about 15 minutes to swap them

Originally Posted by msuka

Had to bump this up, this is going to help me a lot with my 3.64 swap from a z4 may also have to change the drive shaft as well for my 330.

why would you have to change the driveshaft on the 3.64 diff. this thread is about the small diff out of the X3..pay attention.

no need to bump threads with no questions asked and bump others off the front page that matter.

I am picking up a diff from a z4 and my car is 330, no need to be a prick about it just trying to get a little help.

I have a question? Ive read all this thread and i seem to understand it well and think its a great way to easily get more out or you car at a little extra mpg but i was wondering, i do a lot of motorway driving and mileage and would this method work the other way around? I have a 3.38 and if i could live with a little slower off at the lights and wanted more MPG then could i use a lower type diff to bring the rpm down on the motorway and save on the long hauls? Could this work? I have a second car for hard driving so dont need more torque from my bimmer.

If you do a lot of motorway driving, then this is not for you. I do 100 mph at 4000 rpm.

Originally Posted by Muffeater

I have a question? Ive read all this thread and i seem to understand it well and think its a great way to easily get more out or you car at a little extra mpg but i was wondering, i do a lot of motorway driving and mileage and would this method work the other way around? I have a 3.38 and if i could live with a little slower off at the lights and wanted more MPG then could i use a lower type diff to bring the rpm down on the motorway and save on the long hauls? Could this work? I have a second car for hard driving so dont need more torque from my bimmer.

well you might use more gas trying to get your 318 up to speed in city driving. but when it is on the highway and cruising flat, yes a lower diff ratio should help your gas mileage(as long as your car's engine isn't too far out of it's best powerband).

Originally Posted by Alex323Ci

well you might use more gas trying to get your 318 up to speed in city driving. but when it is on the highway and cruising flat, yes a lower diff ratio should help your gas mileage(as long as your car's engine isn't too far out of it's best powerband).

So if i was to get the ECU chipped or mapped to bring the power band down would this help the car pull better on highways when you go to over take someone, instead of it taking too long,and pulling away from the lights in the city or would this just be pointless cause it would be canceling out the purpose of changing the diff in the first place? If you get me!

thinkin of doing this was the install hard how much you think a regular mechanic shop would charge?? so it would be fairly easier to install into a 328 as it was on your 330 correct FYI most mechanics are dumb!

Originally Posted by VERDUGO135

thinkin of doing this was the install hard how much you think a regular mechanic shop would charge?? so it would be fairly easier to install into a 328 as it was on your 330 correct FYI most mechanics are dumb!

You want to take this to a regular mechanic shop, then go on to say that most mechanics are dumb?

It'll probably cost You a couple hundred dollars. It's easy enough to do Yourself

hi,

i have a source to get a 3.91 diff off from a e46 320I (euro). Is it a directly bolt on like other diff for my e46 325I? thanks

Ken... I have a couple of questions for you; 1)Does the 330Ci have the same shorter driveshaft set-up as the 330i? 2)Is the 323 driveshaft just as durable as the 330's?, and does "spacing" it a bit compromise it even more? 3)I love your set up, BUT Im thinking of swapping the front input flanges as well, and "lengthening" the stock 330Ci driveshaft at my Hot rod shop? They would cut, add a piece, and balance the driveshaft. Whats your take on all this? is it overkill, or prudent and worth the extra effort?

Originally Posted by BeMyWhip

Ken... I have a couple of questions for you; 1)Does the 330Ci have the same shorter driveshaft set-up as the 330i? 2)Is the 323 driveshaft just as durable as the 330's?, and does "spacing" it a bit compromise it even more? 3)I love your set up, BUT Im thinking of swapping the front input flanges as well, and "lengthening" the stock 330Ci driveshaft at my Hot rod shop? They would cut, add a piece, and balance the driveshaft. Whats your take on all this? is it overkill, or prudent and worth the extra effort?

Yeah, if you have an auto, you have the same short driveshaft. It doesn't affect anything to "space" it. I think it's overkill to do #3, that's a lot of work. The 323 driveshaft is just fine, I'm running a supercharger on the car with it, and it's been ok.

Originally Posted by kpeng

Yeah, if you have an auto, you have the same short driveshaft. It doesn't affect anything to "space" it. I think it's overkill to do #3, that's a lot of work. The 323 driveshaft is just fine, I'm running a supercharger on the car with it, and it's been ok.

Great stuff Ken. So simple and affordable thats its hard to pass up such a great mod. I was looking into the ZHP rear with the lower 3.64, but you got me siked-up for the 3.91. Thanks for the all the great info. Now I just gotta do some internet and salvage yard hunting for the rear and driveshaft.

www.car-part.com

Originally Posted by kpeng

www.car-part.com

Thanks again Ken, but I read the entire thread; I already got all the links. I usually read through the posts so I dont contribute to all the redundency. Gotta admit, you have some good threads! Your header thread was a big help with my purchase and install. One off topic question: How much did you like/feel your supercharger? Was it worth it(it is expensive)? Did you install it yourself? Did you do a "everything you need to know about s/c" by Kpeng thread? lol

So let me get this straight. I can take the 3.9x out of an X3 and put it in my 325i 5speed without problems. Just swap bolts? Sweet! Does anyone know if any X3's came factory LSD?

Originally Posted by NerdCore

So let me get this straight. I can take the 3.9x out of an X3 and put it in my 325i 5speed without problems. Just swap bolts? Sweet! Does anyone know if any X3's came factory LSD?

yes to your first questions. No to your second question. BMW stopped using LSD in non M vehicles and switched to electronic traction control somewhere in the e46 years, possbily in the late e36s...

So lame.....