Anyone know about Diffs/LSD/Final ratios?

Gibbo

Gibbo

Gibbo

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Hi there

Being in a couple of M3's now running 4.10 and 3.91 final ratios and the extra get up and go is noticable. Owners who have done it say it improves acceleration more so than a remap which is impressive as remap transformed my car so if I can achieve similar again then great.

With gearing over 200mph and 8300rpm redline loose some top speed is no concern to me though I do feel 3.91 gear will be better suited for a track car than 4.10 otherwise on some tracks I'll need 5th and potentially 6th.

A video that's being floating around the web showing three cars:



Why the thread?

Well I am clueless on Diffs and in case I diss like it then it's hard to reverse once done.

So I've being offered a complete E46 M3 differential supposedly in working order for £150, so I could buy this and then I assume I need:-
BMW Motorsport 3.91 or 4.10 crown and pinion kit
Refurb/rebuild kit new bearing or whatever, the LSD itself?
Professional fitter to do it all.

So is that all I need if this £150 is a duffer will the above make it like new or are more items required?

Sorry if dumb questions but differentials I am not so sure about, some M3 guys even change the LSD type too for more traction out of low speed corners if that makes any sense?


With the car nearly done, I am thinking that with it around 1350kg (with cage), 3.91 or 4.10 gears and 380BHP I'll have one extremely quick car, weight should be bang on 50/50 too. :)
 
Going to be watching this with interest as my box will be getting rebuilt next year with a Quaife ATB differential and be good to see what others have to say about gearing at the same time. I chose one of these over the adjustable 'plated' LSD's as you get the best all rounder (On my car at least), I spoke to numerous people who have adjustable diffs and apparently they are superb on track once set up but a bit of a pig if you want to use it on the road.
 
I'll be watching too.. I've been looking at the 4.77 for the S2000 - I've been advised you need a ring and pinion kit which contains some seals (also the bearing if you want) and you'll need a box to send the right signals to the speedo.

Keep us posted.
 
AmDaMan said:
I'll be watching too.. I've been looking at the 4.77 for the S2000 - I've been advised you need a ring and pinion kit which contains some seals (also the bearing if you want) and you'll need a box to send the right signals to the speedo.

Keep us posted.
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I looked at doing this when I had an S2000.

There was a bit of challenge actually getting parts to do this - I think most people in the states were getting the parts from some random Korean 4x4? - but theres a guy on S2Ki who you can get all the parts from who I think lives in Florida.

The differences looked amazing on the S2000 (makes the car fly through the gears) and in reality, the S2000 probably doesn't lend itself to doing 174MPH anyway :)
 
Conanius said:
I looked at doing this when I had an S2000.

There was a bit of challenge actually getting parts to do this - I think most people in the states were getting the parts from some random Korean 4x4? - but theres a guy on S2Ki who you can get all the parts from who I think lives in Florida.

The differences looked amazing on the S2000 (makes the car fly through the gears) and in reality, the S2000 probably doesn't lend itself to doing 174MPH anyway :)
Click to expand...

It uses the gear from a Kia Sportage, here in NZ the kit is $800 but some bloke does them for $350 in the States! Yeah it's awesome, especially if it isn't a daily that uses the motorway a lot.. The recent S2000 video of the guy who was going round the Nurburgring with one hand uses the same ratio and you can see just how rapid it is.. It might not be practical for me if I run boost but I think it would still be fun. :D
 
4.1 FD best for track imo, if your gonna do it go all the way. Pig on the road though so take that into account. I seem to remember the gear kits costing a fair bit.

Bear in mind SMG though. I remember when folk started fitting these there was some issue with changing gears at full throttle. That was some time ago now though so there's probably a solution out there.
 
HummuH1 said:
4.1 FD best for track imo, if your gonna do it go all the way. Pig on the road though so take that into account. I seem to remember the gear kits costing a fair bit.

Bear in mind SMG though. I remember when folk started fitting these there was some issue with changing gears at full throttle. That was some time ago now though so there's probably a solution out there.
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Will be an issue with SMG if in auto mode, as the RPM it thinks to change out would be different with a different ratio fitted, so simply do not drive it in auto flat out, which I never do anyway.

In manual an SMG works just like a manual. :)
 
Gibbo said:
Will be an issue with SMG if in auto mode, as the RPM it thinks to change out would be different with a different ratio fitted, so simply do not drive it in auto flat out, which I never do anyway.

In manual an SMG works just like a manual. :)
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Aye I know, owned a couple of SMG's. Never used auto in the 3 years or so I had the SMG cars.

Can't remember exactly what issues were as is was 8/9 years ago I was playing around with mine but I do recall that it affected manual changes on WOT. Like I say, won't be anything to worry about as plenty of folk run the shorter FD's with SMG so if you do face any teething issues there will be a solution out there.
 
Conanius said:
I looked at doing this when I had an S2000.

There was a bit of challenge actually getting parts to do this - I think most people in the states were getting the parts from some random Korean 4x4? - but theres a guy on S2Ki who you can get all the parts from who I think lives in Florida.

The differences looked amazing on the S2000 (makes the car fly through the gears) and in reality, the S2000 probably doesn't lend itself to doing 174MPH anyway :)
Click to expand...

Does this make motorway cruising an even higher rpm? I think motorway speeds equate to about 4000 rpm anyway on the S2000. Would be great to have quicker acceleration!
 
sovietspybob said:
Yeah there's no way i'd do it in a car which would ever see normal road driving.
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Its quite fine in the M3 to be honest, due to how high its rev limit is and very tall stock gearing. A lot of guys use 4.10 even in road cars with no issue, but I am steering towards the 3.91 :)
 
I would just go down the 4.1 route. Even then it's only 3200rpm at 70 so completely fine on the road still.
While you have the diff apart, ditch the visco lok centre and put the M3 evo salisbury type one in, it will give the diff a more consistent and predictable locking.
 
Clarkey said:
I would just go down the 4.1 route. Even then it's only 3200rpm at 70 so completely fine on the road still.
While you have the diff apart, ditch the visco lok centre and put the M3 evo salisbury type one in, it will give the diff a more consistent and predictable locking.
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Cheers m8.

I believe it is something along the lines of 80mph is 3000rpm stock on E46 M3 and 4.10 takes it to 3500-3600rpm at 80mph in top. 3.91 a little low.

Top speed in 3rd is like 100mph stock and with a 4.10 around 92mph I think.

So yeah its not a drastic change but the acceleration difference is quite noticeable. :)
 
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