final drive swap

tintoverano · Mar 23, 2020

hi,

I could get an automatic final drive (3.73) for a nice price, the manual is 3.64 in a 23i - I know it is not a lot of gain, but the price is an inviting one

would it fit into the manual?

if yes, can it be done DIY? (seems to be, at least for other models)

did anybody swap to higher (or lower) ratio final drive?

thanks

Anonymous · Mar 23, 2020

tintoverano said:
hi,

I could get an automatic final drive (3.73) for a nice price, the manual is 3.64 in a 23i - I know it is not a lot of gain, but the price is an inviting one

would it fit into the manual?

if yes, can it be done DIY? (seems to be, at least for other models)

did anybody swap to higher (or lower) ratio final drive?

thanks

Why?

tintoverano · Mar 23, 2020

researching the topic is fun - looking at 3.91 final drives' fit right now

swapping to higher ratio would increase torque at the wheel (and lose some top speed)

the 2.5l N52B25 has not much room for tuning

brillomaster · Mar 23, 2020

back in the day, i swapped a 2.93 diff to a 3.43 diff in an old E46 328i track car. Was a great mod, nice and punchy through the gears and great pull out of corners. sure the cruising rpm on a motorway went up by 500rpm, but for a track car id say it was worth the £50 i paid for the diff.

Top speed not a concern, even the longest tracks the car never topped 120. it did make 5th gear actually useable though (conversely made 1st almost redundant)

however, my swap was 17% shorter geared... going from a 3.64 to a 3.73 is only 2% shorter, which you're hardly gonna notice. either do it properly and get a 4.00 or higher, or dont bother!

tintoverano · Mar 23, 2020

I agree about the gain with 3.73, the price gave the whole idea

as I wrote, I'm already after 3.91 - approaching with the least change required mindset

these come with different input flange parameters, smaller than my final drive has - looking at ways to change the flange

Anonymous · Mar 23, 2020

tintoverano said:
I agree about the gain with 3.73, the price gave the whole idea

as I wrote, I'm already after 3.91 - approaching with the least change required mindset

these come with different input flange parameters, smaller than my final drive has - looking at ways to change the flange

Not sure where you are going to be in 6 months time if this self isolation is still on then? :rofl:

Have you looked at putting a V8 unit in?

With a turbo and supercharger? :rofl:

tintoverano · Mar 23, 2020

Pbondar said:
Not sure where you are going to be in 6 months time if this self isolation is still on then? :rofl:

Have you looked at putting a V8 unit in? With a turbo and supercharger? :rofl:

I'll think about it

MACK · Mar 27, 2020

brillomaster said:
back in the day, i swapped a 2.93 diff to a 3.43 diff in an old E46 328i track car. Was a great mod, nice and punchy through the gears and great pull out of corners. sure the cruising rpm on a motorway went up by 500rpm, but for a track car id say it was worth the £50 i paid for the diff.

Top speed not a concern, even the longest tracks the car never topped 120. it did make 5th gear actually useable though (conversely made 1st almost redundant)

however, my swap was 17% shorter geared... going from a 3.64 to a 3.73 is only 2% shorter, which you're hardly gonna notice. either do it properly and get a 4.00 or higher, or dont bother!

I've done something similar on my pre facelift E85 3.0i SE
I changed the standard 3.07 diff for one from a pre facelift 2.5i Auto. The ratio is 3.64. As all the E85/6 (including the M, but excluding the 2.0) use basically the same gearbox with the same ratios, I've effectively matched the ratios of a Z4M (I'm also using the M tyre sizes). Allowing for the 5% extra profile means I've also matched the overall gearing of an E86 Coupe which runs a 3.46 diff as apposed to the 3.23 the post facelift 3.0si roadsters use.
It's made a huge difference, the best mod I've made and really livens the car up. I believe the diff changes made on the facelift cars is the major factor in them feeling more energetic than the pre cars. A bigger factor than the engine change/extra BHP. The only detriment is the car now revs about 300-400 revs higher for a given speed on the motorway but nothing worse than you see in the 5 speed 2.2/2,5i pre facelift models IIRC.
I've even tried it with a spare set of wheels running the smaller standard tyre profiles and to be honest didn't feel the gearing was too short, just a lot of fun!

tintoverano · Mar 27, 2020

thanks for the feedback on this

I'm onto something already, once I have results I'll post here

tintoverano · May 17, 2020

finally, this week I swapped the differentials

put in the one I mentioned above: 3.73, coming from an automatic (wanted to go shorter, but there was none available at the time)

muscles are still sour

these beasts weigh a lot

so, refurbished the new completely and also added Racing Diffs' LSD, to make the whole thing justifiable :rofl:

if there's interest, I'll do a how to and definitely tell later how driving the car feels now

so far all looking good, cornering speeds are increasing day by day :driving:

want a converted 3.64 differential?

let me know, we can make a deal

Heebs84 · Apr 7, 2023

Tintoverano I’m looking to do what you did I have a 3.0si manual e86 I bought a Quaife lsd but want to change the gearing to a 3.73 but I’m not sure what rear diff will fit work. Also it looks like I have to buy the whole diff instead of the gear & pinion did you end up just swapping them out? Fix up the new one with the Quaife and then just pull the original? I appreciate your help in the matter

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