Putting auto rear in 5spd ?

[GuitarKid93]

I was wondering if putting a auto rear in my 5 speed what the out come will be, better or worse, I wasn't sure the ratios of the cars both 93 325i's...

[bloxsom]

u have a 3.15 open diff. i got a diff out of an auto 98m3 that had 3.38
but u will have worse mpg but harder acceleration!
it depends on the year and what your looking for, tell us what your looking for!

[GuitarKid93]

I bought a 1993 325i rear from a auto, and my car is a 5 speed, is this a bad idea to swap ? im not looking for anything i have them both

[tokbandit]

the auto diff in a 93 is an open 3.91 .....if you put that in your 93 5sp....forget about gas mileage cause you wont have any......and you will have a very low top speed ...but just think about what you want to do....are you going to use it just for racing...or a daily driver....in my book it would be a bad idea....but its your car...your money...

[makenzie71]

3.91 won't be too bad...but you are going to lose a lot of your highway economy. If you drive around town like a sane person then not much will change there.

[Mitch]

3.91 puts him at ~4k rpm at 70mph in 5th gear. Sorry, no way.

[jiggynites]

yeah the 3.91 is a gas killer and only way to bring it down is to use some 18-19" rims with the widest tires you can fit to bring it down to at least 3.71. also from what i see 5th gear will top out at 119mph-128mph depending on your rim size.
but on the plus side it will make your car feel like a torque monster. basically a poor mans supercharger.
Im actually gonna leave my stock 3.91 diff when i do my manual swap in 2 weeks just for the hell of it until i get tire of it then i ll put the 3.15.

[Mitch]

yeah the 3.91 is a gas killer and only way to bring it down is to use some 18-19" rims with the widest tires you can fit to bring it down to at least 3.71. also from what i see 5th gear will top out at 119mph-128mph depending on your rim size.
but on the plus side it will make your car feel like a torque monster. basically a poor mans supercharger.
Im actually gonna leave my stock 3.91 diff when i do my manual swap in 2 weeks just for the hell of it until i get tire of it then i ll put the 3.15.
1st gear will be useless

[jiggynites]

pretty much

[randytt]

i have one in my car and its not too bad... i just came back from a little road trip and it is alright on gas.. i got about 23mpg going about 70-80.. at 70mph i am at about 3.5k and 80mph is a little over 4k... other than that i think the 3.91 is great... and very fun when u get on it...:devillook

the ratio is a little too short for me because i drive on freeways alot.. but i can deal with it till i get a deal on a 3.23LSD

[GuitarKid93]

I have 18 inch wheels, can't wait to see how much diffrent it is, im ordering the tuner motor sports chip also should be nice when i get it all back together, I was told lighter wheels make a huge diffrence cause mine are really heavy, worth changing ?

[GuitarKid93]

Is the auto rear possy ?

[NHbmw325I]

I think it depends on if you get the winter package, I know that mine is open.

[GuitarKid93]

alright thanks guys

[GuitarKid93]

Any idea what this will do to the 0-60 time with the rear and the new chip

[GuitarKid93]

Bump