Differential suggestions plz

[Marcus33]

Hey guys,
My diff is dead.
My car:
AA stage 1 C38 supercharger
M50 manifold
Dinan exhaust.
What differential would you guys suggest? My cars my summer daily driver, but I do a few auto-x sessions a summer. I also want to be able to drive it on road trips without killing gas milage.
I was thinking of going with metrix's 3.46lsd 40% lock
What would you guys run with my setup/ car usuage?

[kevinwilly]

3.46 with a supercharger? Dude... that thing is going to cook the tires.

I think you might want to post up in the FI section and see what they recommend. I'd almost be tempted to go to a longer ratio diff like a 2.93 if I had FI. But if you go to the track, it would be less than ideal.

I'd agree you'd want 40% lock, though.

[scooper]

Depending on what kind of power you're putting out a custom 3 or 4 clutch 3.15, 3.23, or 3.38. I have a NA 3.46 and it's great for my set-up. With a supercharger I agree it would be too short unless you like shifting every 1-2 seconds.

[Inicent Child]

I would go with the 3.46.

My buddy has his stock 3.15 and its way to damn long. My other friend runs a 3.38 and it doesn't seem to create any traction problems and you don't have to shift that much more.

If traction is ever a problem, get a better tire compound or go wider.

[esp42089]

My buddy got a 20-50 variable ramp lsd 3.38 in his twinscrew 330ZHP, it is really awesome. It's hard to describe, but it is like it slingshots you out of turns. Really even delivery of power on exits. Can't remember who he ordered it from though.

[stanksbeamen]

I'd say stick with the 3.23 or go with a 3.38. Anything higher maybe a PITA when cruising on the highway.

http://diffsonline.com/techinfo/index.shtml

There is a spread sheet at the bottom of that page, you plug in your diff/tire sizes and see what you like...

[Mpwner]

I would go 3.23 or 3.15... shifting every 2 seconds is annoying.

[CrazyxMidget]

get the 750i conversion kit with the 3.15

[RRSperry]

Ok, I actually have a supercharged M3 with a 3.38 diff.

With any centrifugal supercharger, you don't make max boost until you reach max RPM's. You WANT to be in the upper RPM's when you WANT to go fast.

If your diff is really dead, get a 3.38 or a 3.46. I've seen 40% 3.46 diffs from Matrix on ebay for $1000. Brand new, with a warranty. Either will be fine. With the 3.38, rpm's are 3750 at 80 mph. Very livable... A 3.46 will be about 120 rpm higher. (3870)

Oh, with good tires, traction isn't an issue.

[pbonsalb]

I ran 3.23, 3.38 and 3.64 with a supercharger and am now running 3.15 with a turbocharger. I like the 3.38 as the best overall daily driver factory LSD. You can find them used for $500. The 3.46 LSD is aftermarket only and more expensive but also a good choice.

The 3.64 and beyond are only for the hardcore if you drive much on the highway -- I got tired of it and decided to put the 6 speed conversion money towards the turbo that makes enough torque that it is much faster with a 3.15 than the supercharger with a 3.64. 4000 rpm at 80 on the highway is fine for 30 minutes, but gets old fast on longer drives.

You can find an XLS spreadsheet gearing/mph calculators at www.diffsonline under Technical. I determined that 255/40/17 rear tires made my 3.64 more like a 3.58.

[Marcus33]

What are you running for tires?


Ok, I actually have a supercharged M3 with a 3.38 diff.

With any centrifugal supercharger, you don't make max boost until you reach max RPM's. You WANT to be in the upper RPM's when you WANT to go fast.

If your diff is really dead, get a 3.38 or a 3.46. I've seen 40% 3.46 diffs from Matrix on ebay for $1000. Brand new, with a warranty. Either will be fine. With the 3.38, rpm's are 3750 at 80 mph. Very livable... A 3.46 will be about 120 rpm higher. (3870)

Oh, with good tires, traction isn't an issue.

[RRSperry]

Hankook Ventus RS-2's? 245-40-17

[weaksauce]

I ran 3.23, 3.38 and 3.64 with a supercharger and am now running 3.15 with a turbocharger. I like the 3.38 as the best overall daily driver factory LSD. You can find them used for $500. The 3.46 LSD is aftermarket only and more expensive but also a good choice.

The 3.64 and beyond are only for the hardcore if you drive much on the highway -- I got tired of it and decided to put the 6 speed conversion money towards the turbo that makes enough torque that it is much faster with a 3.15 than the supercharger with a 3.64. 4000 rpm at 80 on the highway is fine for 30 minutes, but gets old fast on longer drives.

You can find an XLS spreadsheet gearing/mph calculators at www.diffsonline under Technical. I determined that 255/40/17 rear tires made my 3.64 more like a 3.58.

actaully the 3.46 is a e28 gear ring and pinion and can be swapped into the e36 carrier.

i'd recommend the 3.23 or 3.38 if it was me.

when i twin screw my 95 i'll just freshen up the 3.15 in it since i bet it will be plenty of diff for a ts setup.

[orangehatter]

Rebuild what you have.

:)

[pbonsalb]

actaully the 3.46 is a e28 gear ring and pinion and can be swapped into the e36 carrier.



The secret swap recipe is known to only a select few. I have a friend with a couple of those e28 diffs and he has not found any parts lists or instructions yet. Theoretically, it should not be as hard as the select few suggest, but there are very few DIYs out there for the diff gear swap.

[RRSperry]

The info is in the TIS. You just have to look under the E30 M3 section. You really do need a good micrometer, dial indicator, and machinist's gear blue paste. (or yellow, you can get it at GM dealers.) Setting the clearance and back lash, and tooth contact patten is critical, along with the front pinion bearing preload. You can get all the parts needed from DAn at Diffsonline, or Bimmerworld.

It's not rocket science, people have been building differentials for 100 years.

[pbonsalb]

I want the U Tube video.

[orangehatter]

The secret swap recipe is known to only a select few. I have a friend with a couple of those e28 diffs and he has not found any parts lists or instructions yet. Theoretically, it should not be as hard as the select few suggest, but there are very few DIYs out there for the diff gear swap.

The TIS, as mentioned by RRSperry, is helpful. I've also found a few numbers through Metric Mechanic. Essentially these are the numbers you are looking for:

Ring and Pinion Backlash = 0.06 mm to 0.14 mm
Pinion Preload = ~13 in-lbs to 17 in-lbs

I have been documenting my 3.46 build on a local forum:
http://ohiobimmers.com/forum/showthread.php?t=3624

The link should answer a lot of the questions you would have about building.


You can get all the parts needed from DAn at Diffsonline, or Bimmerworld.


I wouldn't bother with Diffsonline. It's fairly simple to get the correct bearings without paying for someone's "secret recipe." I'll give you the "secret" parts recipe.

Here's the numbers you need for the bearings and races:

LM503310 Carrier Race x2
LM503349A Carrier Bearing x2
HM89410 Pinion Race x1
HM89449 Pinion Bearing x1
HM88510 Pinion Race x1
HM88542 Pinion Bearing x1

Timken, National, FAG, Fafnir, SKF, INA, etc. are all good brands. To find the correct bearing, an example search would be: "Timken LM503349" for the carrier bearings.

Now Bimmerworld is useful for getting the clutches. They are $75ea for a 188mm diff if you are keeping the stock 25% lock up. For 40% lock you will need a third clutch and dog ear plate and will have to machine the inside of the limited slip spool to fit the additional clutch and plate.

[Stuntman]

OS Giken 1.5-way LSD.

De-activate 1-2 plates per side and call it a day.

[rayesc]

3.38 + SC would be fun. I'm sporting a 3.38 on an otherwise stock car. Its definitely noticeable compared to the coupe with stock diff, but not so much that I get crazy wheel spin on launch. Note, I'm sporting 285 rear tires.

[Volf]

With a S/C the highest I'd go is 3.38s

[Marcus33]

Added poll

[pbonsalb]

With a S/C the highest I'd go is 3.38s

That is what I had with an SC until I drove an SC car with 3.64s that was like a slingshot in comparison. But definitely a compromise if you do more than 30 minute highway drives at over the speed limit.

[orangehatter]

Honestly, if you have a supercharger you already have the power and torque that will make the car quicker. You should shoot for a higher ratio like 3.15 or 3.07 rather than something low like 3.46. You will find that you are in and out of gear like crazy. Just going to 3.46 will drop your speed in first gear by about 5mph, and even more through all of the other gears. N/A cars are best with lower ratios and FI cars are best left with higher ratios.

[pbonsalb]

You can never have too much power. The stock M3 is perfectly adequate. The OP has a supercharger on top of adequacy. And he obviously still wants more.

With a supercharger, I went from 3.23 to 3.38 to 3.64. And I still wanted more. That led me to either a 6 speed conversion to make the 3.64 more liveable on the highway or to a turbo conversion. Contrary to popular belief, the centrifugal supercharger adds relatively little torque. The turbo, however, adds massive torque. That is because it produces full boost in the midrange rather than the centrifugal supercharger's fraction of full boost. With the turbo, I went down from the 3.64 to a 3.15 and would have gone to a 2.93 if an inexpensive LSD version was available, and my car is still significantly faster than it was supercharged with the 3.64.

[RRSperry]

Honestly, if you have a supercharger you already have the power and torque that will make the car quicker. You should shoot for a higher ratio like 3.15 or 3.07 rather than something low like 3.46. You will find that you are in and out of gear like crazy. Just going to 3.46 will drop your speed in first gear by about 5mph, and even more through all of the other gears. N/A cars are best with lower ratios and FI cars are best left with higher ratios.

That's just kind of wrong with superchargers.


Seriously, with a 5 speed car, 3.46 is as short as you want to go if you have to drive it on a highway. You can go to 3.64 if you have, or want to install a 6 speed.


Anyway, welcome to the world of "You get to PAY to play"...

[orangehatter]

The turbo, however, adds massive torque. That is because it produces full boost in the midrange rather than the centrifugal supercharger's fraction of full boost. With the turbo, I went down from the 3.64 to a 3.15 and would have gone to a 2.93 if an inexpensive LSD version was available, and my car is still significantly faster than it was supercharged with the 3.64.

The other reason that you need 2.93, 3.15, etc. for a turbo is the strength of the gears too. The tooth count on a 2.93 ring gear is way less than that on a 3.46. Fewer teeth = thicker teeth = stronger teeth. That's why a 188mm 2.93 set can hold ~480ft-lbs of torque before breaking teeth, whereas the 3.46 is down closer to ~400ft-lbs, and the 3.91 is even less at ~370-380ft-lbs.

[AgentHubcap]

I'm getting a custom diff built up, and wanted suggestions similar to the OP. I'm currently NA and probably will be for a while. I also currently have a 3.38 and do not DD my car.

I was thinking of going with a 3.46 torsen diff. Is that a good choice, or should I stay with a clutch-style?

[orangehatter]

Torsen requires much less maintenance. Clutch style...well, you have to replace the clutches every so often.

[pbonsalb]

I'm getting a custom diff built up, and wanted suggestions similar to the OP. I'm currently NA and probably will be for a while. I also currently have a 3.38 and do not DD my car.

I was thinking of going with a 3.46 torsen diff. Is that a good choice, or should I stay with a clutch-style?

If you do not daily drive the car, why not go to a 3.64?

[gradon]

OP: If you're gonna spend $1K, spend it on the 3.46, or else wait until a $500 3.38 shows up.
Agent: I wouldn't spend the money for a 3.46 if I already had a 3.38--go 3.64 if you want to play, cause you won't really notice a difference with a half-step up. I bought a 3.73 lsd(I'm assuming it has a stock 25% lockup)for $402 shipped and I don't mind being at 4.1K@80 mph(which is 15-25 over the limit around here anyhow--but I go there). I wasn't looking for a 3.73 and would've spent the same $ on a 3.38, but am glad I didn't. I say use the 3.38 and spend money on other things.

[Marcus33]

Figured I'd give an update. I ended up going with a Metrix Motorsports 3.46 40% lock diff. I'm still in the break in period, but i have to say I love this ratio. The car just feels so much quicker, I love it. Thanks for all the input. !