Differential Upgrades

Mikey_Boy · Post by **Mikey_Boy** » Wed Aug 15, 2018 10:46 am

Thanks for the advice!

But darn it, I wish I'd not seen the vids of the cars running 3.91 diffs - looks like a super upgrade......!

More thinking / saving to do...!

Simon 3.2M · Post by **Simon 3.2M** » Thu Aug 16, 2018 12:52 pm

Who would you use to rebuild it / replace the seals?

BMWZ4MC · Post by **BMWZ4MC** » Sat Aug 18, 2018 1:48 am

As testimony to the durability of the standard differential, I have used my ///M as a track car for nine years covering thousands of miles without any problems.

robjones888 · Post by **robjones888** » Sun Aug 19, 2018 9:56 am

http://www.jcracing.info/

In Thirsk

Speak to theses chaps as build loads of diffs for M3’s running in most race series throughout the U.K.

Mikey_Boy · Post by **Mikey_Boy** » Thu Aug 23, 2018 6:11 pm

Thanks All!

Looks like I'll be going for rebuilding the standard diff with a 3.91 ratio - watch this space...

Vanne · Post by **Vanne** » Tue Aug 28, 2018 11:44 am

Interesting..

exdos · Post by **exdos** » Tue Aug 28, 2018 1:08 pm

Mikey_Boy wrote: ↑Thu Aug 23, 2018 6:11 pm Thanks All!

Looks like I'll be going for rebuilding the standard diff with a 3.91 ratio - watch this space...

I did a diff ratio swap on my Z3MC in 2010 from OEM 3.15 to 3.46. When I did some datalogging from the ECU using various parameters, the swap didn't make any significant difference to on-road performance and just increased fuel consumption. For me, it was a waste of time/money and I went back to the OEM ratio.

Mikey_Boy · Post by **Mikey_Boy** » Fri Dec 07, 2018 2:19 pm

Good to know Exdos - I'm still pondering this one...

bradz · Post by **bradz** » Thu Dec 13, 2018 10:35 pm

I have just taken the plunge and purchased a Gripper 12 Plate diff & BMW 4.10 final ratio.

This is for my e46 M3 though (Track car)

After doing a bit of research is seams the 4.10 is the one to go for, Takes the top speed down to about 170 but it will get there pretty quickly! apparently its the equivalent of 40bhp

https://www.automac.co.uk are building mine.

Adam

TomK · Post by **TomK** » Thu Dec 13, 2018 11:24 pm

bradz wrote: ↑Thu Dec 13, 2018 10:35 pm I have just taken the plunge and purchased a Gripper 12 Plate diff & BMW 4.10 final ratio.

This is for my e46 M3 though (Track car)

After doing a bit of research is seams the 4.10 is the one to go for, Takes the top speed down to about 170 but it will get there pretty quickly! apparently its the equivalent of 40bhp

https://www.automac.co.uk are building mine.

Adam

Cool

let us know how you get on with it! I've heard really good things about the gripper and been looking at the same solution, it makes a lot of sense in terms of performance and economics.
For me it'll be an 8 plate and the 3.91 cwp as my car is still supposed to be not too unpleasant on the road (think the 12 plate is a bit on the noisy side?).

bradz · Post by **bradz** » Thu Dec 13, 2018 11:44 pm

Cheers I will do.

Automac who are building it said the 12 plate will be noisy at low speed on the road and will push the front at very low speed. (This was a concern of mine as I still drive to tracks & the ring) They said its not horrific and the way it hooks up on track will make it worth it, They also said when it goes in for its 12 month checkup if I wanted they could change it back to a 8 plate for no extra cost.

That was enough to persuade me to go all out!

TomK · Post by **TomK** » Thu Dec 13, 2018 11:50 pm

bradz wrote: ↑Thu Dec 13, 2018 11:44 pm Cheers I will do.

Automac who are building it said the 12 plate will be noisy at low speed on the road and will push the front at very low speed. (This was a concern of mine as I still drive to tracks & the ring) They said its not horrific and the way it hooks up on track will make it worth it, They also said when it goes in for its 12 month checkup if I wanted they could change it back to a 8 plate for no extra cost.

That was enough to persuade me to go all out!

Can't argue with that! Keep us posted

GuidoK · Post by **GuidoK** » Fri Dec 14, 2018 2:45 am

bradz wrote: ↑Thu Dec 13, 2018 10:35 pm apparently its the equivalent of 40bhp

Thats the result of a very blunt calculation.
Its the equivalent of 44bhp for 77% of the time and a loss of ~82bhp for 33% of the time.
Only when you're in the same gear you have the 44bhp advantage, but with the shorter gears you have to shift up earlier, resulting in much much less wheel torque (and equivalent power).

Its a difficult exact calculation to make. The powerpart when you're in the same gear its easy, but the percentage of time and drop in power when going in different gears is difficult because not every gear is equally spaced. For the percentage I took gear 1-3 (so thats accelerating up to 100mph on the standard final drive), and the loss in power when riding in a higher gear I took the difference between 2nd and 3rd gear (the loss in power between 1st and 2nd is bigger as the corresponding difference in gearing is bigger).
0-60 will be faster with the short ratio but 0-105 will be slower (and 0-90 will be quicker).
So it really depends on what exact speeds you try to reach.
But the +40hp gain is not true (well, its true for 77% just as the loss of ~82hp is true for 33%).
In the end the gain is 0%. The ratio that maximizes the end speed reached wins.

Mikey_Boy · Post by **Mikey_Boy** » Wed Jan 02, 2019 1:18 pm

Happy New Year everyone! I've just spoken with my local Indy and they are suggesting getting a standard diff rebuilt to standard spec is going to be tricky due to lack of parts availability. Not sure how true that is so any advice on that is much appreciated!

Just looking at the above, the gripper diffs are also a tempting option - is there a ballpark price for the build?? I'd probably keep the 3.64 ratio and something not too aggressive as the car is mainly used on the road.

It seems to me to be much easier to just swap the whole unit than have to go through the pain of taking the diff out and then have the car hanging about for weeks whilst the diff is sorted...

As ever, any advice is much appreciated!

R60BBA · Post by **R60BBA** » Wed Jan 02, 2019 3:36 pm

Standard diff is good enough for road use.

If you want a track focused car then I recommend the BMW Motorsport 4:10 diff.

Darragh Doyle (ex F1 tech) @ Everything M3’s can rebuild a diff to your specification at a reasonable price.

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