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sibanez
sibanez New Reader
1/29/21 4:47 p.m.

I was planning to sell my 128i, but things got too crazy so I decided to do a light STX build. 

The 128i comes with a EDiff, and while it works well enough, I'm told that a real LSD will be much better.

I've driven an Integra with a MFactory plate-type LSD, and a few Civic SIs with helical LSDs. My BRZ had the factory LSD and I could really feel it working on the autocross course.

My questions is, what's the performance difference between a helical and clutch-style in a RWD 128i? I'll be running 245/40R17s A052s with about -3.5 degrees of camber up front. Car is currently making 219whp/214tw and is riding on Red Shift coilovers. 

My hesitancy on the clutch-type is A) Maintenance and B) Cost. I did fluid changes on my Integra after each HDPE, and was able to drop the transmission quickly after a few necessary changes. I'm planning to keep the factory seats in the car, and won't be doing much more beyond the tune/coilovers/swaybars/exhaust/intake/wheels/tires. I won't be at the pointy-end of driving, but want it to be competitive locally with a few trips to champ tours in the mix. 

Thoughts?

spacecadet (Forum Supporter)
spacecadet (Forum Supporter) GRM+ Memberand UltraDork
1/29/21 4:55 p.m.
sibanez said:

 I won't be at the pointy-end of driving, but want it to be competitive locally with a few trips to champ tours in the mix.

A good helical LSD will probably suit your needs perfectly.

i know the really competitive people run a clutch type diff.... but yeah unless you wanna service it often.. just run the helical.

iceracer
iceracer MegaDork
1/29/21 7:03 p.m.

A clutch type can some times be too "limited ". 

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/29/21 7:28 p.m.

Clutch types also hurt turn-in and steering feel, if they are decently tight.  It makes the steering feel mushy because the back of the car is trying to drive straight, so you need more slip angle in the front tires at low inputs.  This is more noticable the closer the wheelbase and track are to being square.

 

Helical diffs are just open diffs with a variable torque split instead of being stuck at 50:50 so they drive very nice.  They do add a ton of heat to the fluid when used in anger, because they basically work off of the principle that you cannot backdrive a worm gear, so there is a ton of gear load/friction involved.  Mazdatrix did testing on their EP road race car and found that the helical would send gear oil temps to the 400F range, while a clutch diff was almost 200 degrees lower.  Probably most of the heat with a clutch diff was coming from the ring and pinion itself. IIRC they also tested a welded diff and the gear oil temps were only a little lower than the clutch diff.

 

The helical was faster, so they used that.  I forget if they added a diff cooler or just paid closer attention to oil change intervals.

 

GTwannaB
GTwannaB GRM+ Memberand HalfDork
1/29/21 7:53 p.m.

What LSD options are there for a 128?  I thought the prices start at over $3k. 

akylekoz
akylekoz SuperDork
1/29/21 8:46 p.m.

I just ordered a Torsen after mich research.

What comes stock with Torsen diffs.

Boss 302 Mustang

Camaro ZL1, Z28

Miata

Cars that we’re meant to turn.  

What comes with plate style LSD?

Cars that want to launch in a straight line.

With a clutch style when throttle is applied the clutches grab, both tires try to do the same thing, this pushes the car straight.

Helical LSD will transfer power to the wheel with traction and help the car to turn to the inside.

Simplified but basically if you prefer for your car to help you turn get a gear style.

 

sibanez
sibanez New Reader
1/29/21 9:52 p.m.

In reply to GTwannaB :

MFactory, Wavetrack, DiffsOnline and a few others offer LSDs that will fit a 128i. Looking at around $1600+, depending on what type.  

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
1/29/21 10:10 p.m.

FYI, I did back to back testing on an OS Giken (clutch pack with many, many, many discs) and a helical. On our cart track with a 2100 lb 160 rwhp car, the clutch pack was worth 1 second a lap on a 63 second lap. This was all due to being able to put down the power better out of tight corners, despite the increase in turn-in understeer.

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
1/29/21 10:19 p.m.

In reply to akylekoz :

Pretty sure the hummer h1 also came with torsens...

The instructions are paraphrased: If you get a wheel in the air, left foot brake. 

akylekoz
akylekoz SuperDork
1/30/21 6:17 a.m.

In reply to Robbie (Forum Supporter) :

Low bias 8.8 Torsen can be found in a Ranger FX4 also.

rslifkin
rslifkin UberDork
1/30/21 8:06 a.m.

Some helical diffs (including Wavetrac IIRC) have some preload, so like a clutch diff, they can still transfer some amount of power with a wheel in the air. 

dps214
dps214 HalfDork
1/30/21 9:43 a.m.
akylekoz said:

I just ordered a Torsen after mich research.

What comes stock with Torsen diffs.

Boss 302 Mustang

Camaro ZL1, Z28

Miata

Cars that we’re meant to turn.  

What comes with plate style LSD?

Cars that want to launch in a straight line.

With a clutch style when throttle is applied the clutches grab, both tires try to do the same thing, this pushes the car straight.

Helical LSD will transfer power to the wheel with traction and help the car to turn to the inside.

Simplified but basically if you prefer for your car to help you turn get a gear style.

 

You'll have to tell Porsche that their cars are only meant to go straight. They've been using clutch diffs since whenever they started putting LSDs in their cars. Now granted, when you put the engine in the right place, you barely need a diff, so they're not super aggressive and have very little preload (and are often more aggressive on decel lockup than accel, to keep the rear end in line under braking). A well built and tuned clutch diff can do amazing things. If you're looking for an easy button off the shelf option, torsen is the way to go.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/30/21 9:53 a.m.

In reply to dps214 :

A helical might actually be kind of scary in a rear engined car, since the torque biasing effects work under braking too.

Never thought about that until you brought that up.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
1/30/21 11:15 a.m.

I think you can set up helicals to have different behavior under braking. 

Porsche apparently used to run spools in the 956 for durability.

Olemiss540
Olemiss540 Reader
1/30/21 12:26 p.m.
dps214 said:
akylekoz said:

I just ordered a Torsen after mich research.

What comes stock with Torsen diffs.

Boss 302 Mustang

Camaro ZL1, Z28

Miata

Cars that we’re meant to turn.  

What comes with plate style LSD?

Cars that want to launch in a straight line.

With a clutch style when throttle is applied the clutches grab, both tires try to do the same thing, this pushes the car straight.

Helical LSD will transfer power to the wheel with traction and help the car to turn to the inside.

Simplified but basically if you prefer for your car to help you turn get a gear style.

 

You'll have to tell Porsche that their cars are only meant to go straight. They've been using clutch diffs since whenever they started putting LSDs in their cars. Now granted, when you put the engine in the right place, you barely need a diff, so they're not super aggressive and have very little preload (and are often more aggressive on decel lockup than accel, to keep the rear end in line under braking). A well built and tuned clutch diff can do amazing things. If you're looking for an easy button off the shelf option, torsen is the way to go.

And also tell.... Wait for it...... Wait for it.....

 

BMW. Who also used clutch based differentials on some of the most renowned drivers cars of all times.

dps214
dps214 HalfDork
1/30/21 1:47 p.m.

In reply to Olemiss540 :

I thought that was the case, but wasn't as confident on that one so I didn't mention it. FWIW I have no personal experience, but in autocross applications BMWs seem to benefit the most from fancy clutch diffs. Or at least they're the most frequent application...that could be correlation not causation. I have a friend that's building a semi-serious STX 128i and is putting a clutch diff in it, for whatever that's worth.

Tom1200
Tom1200 SuperDork
1/30/21 3:27 p.m.

Count me in the clutch LSD camp. On my Datsun I set the thing up as loose as possible. This seems to negate the turn on understeer.

Snrub
Snrub Dork
1/30/21 9:42 p.m.

What about the conical clutch type diffs in the NC, RX-8 and ND?

djsilver (Forum Supporter)
djsilver (Forum Supporter) Reader
1/30/21 9:48 p.m.

Anything that keeps the rear wheels close to the same speed will affect turn in.  My S2k has a helical diff and I can let off the gas around a curve and the car will turn in by itself.  It's a matter of degree.  I ran an S15 helical in a 240sx and it worked well, but had to drop the rear sway bar to keep both wheels on the ground.  The clutch diff works better in a car when you have enough power to steer it with the loud pedal.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/30/21 10:05 p.m.

In reply to djsilver (Forum Supporter) :

One of the weird things I noted with the RX-7 when I had a very tight clutch diff, or a welded diff (they drove pretty much the same, but the LSD broke fewer axles) was that applying power in a corner, once lateral loads were stable, would pull the nose to the inside.  It wasn't the rearend swinging out like it was sliding, it was more like torque vectoring.  It felt kind of like I was riding in one of those tethered model airplanes and the kid holding the tether pulled it in.

 

This was with a diff shimmed to about 200-250ft-lb breakaway torque.  It made the most hilarious popping/barking noises in low speed tight turns if the roads weren't wet.  Think moving around a McDonald's drive-thru and feeling the suspension wind up and then *CRACK*, wind wind *CRACKACK*, etc...

Vigo (Forum Supporter)
Vigo (Forum Supporter) MegaDork
1/30/21 10:11 p.m.

Ideally any LSD should only transfer as much torque as the tire has traction to use it (considering we're generally talking about unloaded inside tires while turning). In that sense it's easy for a clutch type to overshoot and end up hindering turning more than it needs to while doing no further good for acceleration. A helical LSD somewhat gets around this whole 'tuning dependent' thing while also offering no tunability, lol. I think helical is the 'safest' recommendation for a turning car while someone who's actually going to gather data and spend untold hours tinkering trying to dial in a setup will probably want a clutch type sooner or later almost regardless of what it's in or what they're doing with it (besides drag racing..).

sibanez
sibanez New Reader
1/31/21 5:17 p.m.

Really helpful replies. At this point, I'm going to save my pennies for a DiffsOnline clutch-style LSD. It seems like for a little more money, I can get more performance. I'll drive the car as-is for now, and learn to use what I can. 

 

 

G_Body_Man (Forum Supporter)
G_Body_Man (Forum Supporter) UltraDork
1/31/21 11:19 p.m.

Also keep in mind that if your 1-series is manual, the ring gear is welded to the carrier. A diff out of an automatic car uses a bolted ring gear and will give you a slightly shorter axle ratio while permitting the installation of an LSD.

KyAllroad (Jeremy) (Forum Supporter)
KyAllroad (Jeremy) (Forum Supporter) UltimaDork
2/1/21 6:06 a.m.
Snrub said:

What about the conical clutch type diffs in the NC, RX-8 and ND?

Shhhh, don't let anyone in on the secret.   They work by magic.....my NC diff just worked.  No fuss, no drama, no weirdness, it just worked.   Perfectly.

gumby (Forum Supporter)
gumby (Forum Supporter) GRM+ Memberand Dork
2/1/21 8:17 a.m.
Pete. (l33t FS) said:

Mazdatrix did testing on their EP road race car and found that the helical would send gear oil temps to the 400F range, while a clutch diff was almost 200 degrees lower. 

400°???!!!??!! Dayum.

I delaminated a set of carrier bearings in an 8.8 IRS somewhere north of 250°. I decided if Autometer thought 250° was the top of the reasonable spectrum that I should try to get under that after rebuilding the diff, so I moved the exhaust. I would not have guessed it was anywhere near 400° though and would imagine those guys having bearing problems as well at that sort of temp.

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