Best Differential Ratiol for 500whp Turbo E36 M3?

[nate325]

I have 4 differentials available to me. Sticking with 188mm for now, which ever one is ideal it will rebuilt with 40% lockup.

Power goal is 500whp+, diffs I have now are; 3.15, 3.23, 3.38 and a 3.73. There's also a 420G 6-speed in my setup so this isn't about fuel economy, just the best ratio for that power. Mostly street driven, some autocross, drag strip, and some track use. First hand experience opinions?

[Butters Stoch]

3.15 then 3.23 definitely wouldn't go with the other 2.

[BMWManiac]

+1.....the 3.15 I think is ideal for all around....I have a 2.93 which is great for rolling boost and maybe gas mileage, but from a dead start, it is a bit of a dog

[nate325]

Thanks! Exactly what I was thinking.

[iRodD]

2.93

[chikinhed]

I have a 3.15 and blew up a few 3.23s. I guess the idea is that a lower ratio will 'load' the turbo more but do I really need that? I'm not on bias ply drag slicks that I have trouble spinning in 1st gear that I need to spool my turbo faster from load. I think that the torque multiplication from the higher ratio would make up for it if it was an issue. I think it's good the turbo isn't as loaded as it could be as I really don't need any more torque in first gear and the other gears do just fine. ( and I might be talking out my ass and would love a logical rebuttal)

I guess it all depends on what the ultimate goal is for your car. Drag racer types are probably trying to be at the top of fourth as they cross the 1/4 mile.

Oh and the reason I use the 3.15 is because that is what comes in the 210 diff. I believe that some 188 gear sets are stronger than others (2.93 > 3.23) an that would be a good reason to use them.

Sent from my GTX3582R

[ak5]

Why not use higher ratio with slightly taller tires? You get more tire in that case..

[nate325]

Going with the 3.23 for now with properly sized Super Sports (they run fat).

I have another question related to the driveline... What are the pros and cons of running 6-bolt vs 4-bolt driveshaft? Car came with 4-bolt and I have two 4-bolt shafts ready to fit with the 420G trans... but was considering swapping to 6-bolt (quite expensive considering you need a Euro front half or custom length with the 420G trans). Price isn't really a concern if the 6-bolt with CV is stronger.

Stick with 4-bolt?

[crazyyardie]

Stick 4 bolt or just get the one piece driveshaft and axles. then u have ur rear cross member bolt holes to reinforce

[Skrate]

I doubt there's a "best"

[Butters Stoch]

I doubt there's a "best"

210mm 2.93 ?

[BMWManiac]

I think for those of us that mostly just terrorize on ramps and the street, the best differential is whatever gearing, at your power level, helps you completely hook in 2nd gear....1st is probably useless with any diff, but if you can fully connect in 2nd with your tire/wheel setup, then you have the best diff

For the drag strip, whatever will allow you to again, hook up completely in 2nd gear without riding the hell out of the clutch, and allows you to not have to shift out of 4th gear by the end of the run, from my own personal experience...I think this is more of a personal preference

Never been on a track, so don't know there

[bry195]

390 rwhp 188 dif 3.15 chirps into second. summer street tires.

[angel318ti]

On my setup, 3.23 6 bolt 1st and 2nd are useless. even on 3rd they brake loose on colder tires. I wish I went with a 3.15 to allow me to stay on boost longer.

[Butters Stoch]

On my setup, 3.23 6 bolt 1st and 2nd are useless. even on 3rd they brake loose on colder tires. I wish I went with a 3.15 to allow me to stay on boost longer.

Its not that much of a difference.

[pbonsalb]

With a 3.23, 4th runs out at 130 mph at 7000 rpm and 255/40/17 tires. With a 3.15, it tops out at 133 at 7000 rpm with 255/40/17 tires. Maybe you want a 2.93, which would take you from 130 to 143 mph.

[Matutino]

6 speed 3.38

[pbonsalb]

Does not make any of the gears longer. Just adds an overdrive.

[Matutino]

That's right, the 6 speed makes it freeway friendly with the 3.38

[E36 HateR]

i just switched to 2.79 and i have a 26 inch tire.

I love it, but the 3.15 i had worked great as well.

[graphite9]

^^^clean sedan.

I have a 3.23, and have a 3.15 sitting in the garage. I haven't pulled the trigger, but Im thinking it might make 1st, and 2nd more useful.

[dburt86]

I couldn't imagine a diff lower then 2.93. It's already at 3k at 75mph

[continuing ed]

390 rwhp 188 dif 3.15 chirps into second. summer street tires.

543 whp 2.93 diff chirps 4th on summer street tires. Especially when the waste gate vac line is accidentally pinched. 36+ psi on a 22 psi tune for the win and also for sheared flywheel bolts. In the blink of an eye.

[mcoupemindy]

The one thing that everyone needs to understand is that horsepower is the wrong metric to discuss as far as anything differential related.

I'll be more than happy to provide a solid recommendation, but I need to know more about the car. What TORQUE level are we talking about?

I would never recommend a 188mm 3.38 or 3.23 for anyone over 400wtq. The gear sets are known to be weak and the pinion can break under abuse. 188mm >3.46 and greater should never be used on a turbo car as it would be a reliability issue.

The E36 188mm 3.15 set is OK until about 450wtq in normal circumstances. Your results may vary.

The 2.93 and 2.79 188mm gearset is MUCH stronger due to using a low offset carrier. If you are high torque application, this would be my recommendation if you want to stay with a 188mm differential.

If you really need a 3.15 or higher gearset for a high torque application, you can risk it with a 188mm unit, or go to one of the virtually bullet proof 210mm units.

I've helped out many enthusiasts. If you every want to talk about your rear end (I know Clay is giggling at this), my email is in my signature.

Best,

Jonathan

[Butters Stoch]

The one thing that everyone needs to understand is that horsepower is the wrong metric to discuss as far as anything differential related.

I'll be more than happy to provide a solid recommendation, but I need to know more about the car. What TORQUE level are we talking about?

I would never recommend a 188mm 3.38 or 3.23 for anyone over 400wtq. The gear sets are known to be weak and the pinion can break under abuse. 188mm >3.46 and greater should never be used on a turbo car as it would be a reliability issue.

The E36 188mm 3.15 set is OK until about 450wtq in normal circumstances. Your results may vary.

The 2.93 and 2.79 188mm gearset is MUCH stronger due to using a low offset carrier. If you are high torque application, this would be my recommendation if you want to stay with a 188mm differential.

If you really need a 3.15 or higher gearset for a high torque application, you can risk it with a 188mm unit, or go to one of the virtually bullet proof 210mm units.

I've helped out many enthusiasts. If you every want to talk about your rear end (I know Clay is giggling at this), my email is in my signature.

Best,

Jonathan

Let's say you want to install a 210mm 3.15. But have a 4 bolt DSS shaft. What are your options to adapt the DSS 4 bolt to the 210mm.

Now. Same question with 6 bolt DSS shaft.