SBR "LSD Insert" vs. Welded Diff

[perley03]

Aight, as some of you know, I'm fwd and am looking to improve my traction. I'm debating on buying a LSD insert, but what exactly does the insert do? Does it allow the inside wheel to slip during cornering, or does keep both wheels spinning at all times? If so, then what would the risks of welding the differential be than installing the insert?

By the way, I've already installed the Poly motor mounts, and have a XTD 6 puck clutch.
Suggestions??

 

[definitiveno]

What ive read is that under load from the motor the insert behaves similar to a welded diff, but off load same as an open diff. I would use the indert so that my axles and tires could get a rest under normal driving.


I don't know the rate of engagement though, if it locks under 1/4 throttle, 1/2 throttle, or linearly, etc....

Maybe one of the slowboy chronies can give better details about the activation and function.

 

[PSI NRG]

Welded diff will be MUCH stronger that insert will break over time.

 

[Street Surgeon]

Those inserts are only supposed to be good to a bit over 300hp from my understanding, welded diff's are great if you intend to drive in a straight line all the time I however would stay away from them on a street-car / daily.

 

[jtmcinder]

An insert resists differences in output speeds all the time, but does not stop it completely. A welded "diff" is no longer a diff, since it does not allow a difference in speeds under any condition. (I would not want to try turning onto the exit lane or have to dodge a Starlet with a welded front, but that's a side issue.)

Your best bet is a helical, aka Torsen, aka Quaife, if you can afford it. There are also Asian rip-offs of these, if you are morally impaired.

- Jtoby

 

[Slowboy]

Those inserts are only supposed to be good to a bit over 300hp from my understanding, welded diff's are great if you intend to drive in a straight line all the time I however would stay away from them on a street-car / daily.

I am kinda getting sick of this exact debate, but our inserts have been used in cars with 2-3 times the HP you suggest they are "good for", so please be careful when quoting numbers (no disrespect meant).

My car was well over 500 HP with this insert, and is in no way even clse to the most powerful car that has run it.

For the original poster, if you were to choose a welded diff vs. the insert, I would use the insert. If you have some major cash lying around, call me so we can spend it on a really expensive LSD

Mike Huml

 

[Slowboy]

An insert resists differences in output speeds all the time, but does not stop it completely. A welded "diff" is no longer a diff, since it does not allow a difference in speeds under any condition. (I would not want to try turning onto the exit lane or have to dodge a Starlet with a welded front, but that's a side issue.)

Your best bet is a helical, aka Torsen, aka Quaife, if you can afford it. There are also Asian rip-offs of these, if you are morally impaired.

- Jtoby

GASP....... "you are alive"......

Come see the rally car!

Mike Huml

 

[jtmcinder]

Let me back Mike up with a bit more detail. When talking about the maximums that can be put through a differential, the issue is the strength of the parts that actually transmit the torque, not the piggy-back LSD. As soon as you are talking about the limits of a piggy-back LSD, such as an insert or VC, you have to take the suspension, inter alia, into account, making any general statement -- such as the one Mike objected to -- unwarranted at best. A very well set-up car, in terms of suspension, motor mounts, etc., could go very, very fast on an insert. In contrast, a car with a lousy set-up might be very, very slow even if it had a Quaife.

- Jtoby

ps. yup. still alive and have a better idea: bring the rally car to a winter rallycross and let me drive it!!!

 

[definitiveno]

Hey toby, I know ive asked this in the passed but wonder if your answer may have changed......... for us awder's, would we be better off with our stocker open front diff or with one of these inserts, and for my application I have handling in mind, not drag.

 

[jtmcinder]

I would not use an insert in the front for autocrossing or road-racing. They work in both directions, so they would hurt too much at turn-in for what they do at corner-exit. Save up for a helical. Seriously.

- Jtoby

 

[definitiveno]

They work in both directions, so they would hurt too much at turn-in for what they do at corner-exit.

- Jtoby

So off load coming into a corner with brakes trailing, this insert will still try to equalize tire speeds?

 

[perley03]

I am kinda getting sick of this exact debate, but our inserts have been used in cars with 2-3 times the HP you suggest they are "good for", so please be careful when quoting numbers (no disrespect meant).

My car was well over 500 HP with this insert, and is in no way even clse to the most powerful car that has run it.

For the original poster, if you were to choose a welded diff vs. the insert, I would use the insert. If you have some major cash lying around, call me so we can spend it on a really expensive LSD

Mike Huml

Mike:
What exactly does the insert do, as to cornering, because I do road course and auto-x racing, and an occasional drag here and there. What I'm looking for is something that is not engaged while cornering, allowing me to go through the turns without having the car struggle, and hammer down when coming out of the corners without frying the tires. If it comes down to it, I'll buy either the Kaaz or Qualife helical design, but if I can get away with the insert while meeting my expectations, why spend close to a grand while the insert will do.
Any detailed information on the insert would be greatly appreciated, if you can provide it to me. I may be making a phone call in the near future......

 

[JrCRXHF]

I have the SBR insert in my 1g AWD and i am going to go auto X the car this weekend i will let you know what happens i think it will help the car out coming out of the turn but we will see.

I know it is not as smooth as the AWD setup in my EVO but it does help in the winter i can tell you that.

 

[dsm-onster]

Let me back Mike up with a bit more detail. When talking about the maximums that can be put through a differential, the issue is the strength of the parts that actually transmit the torque, not the piggy-back LSD. As soon as you are talking about the limits of a piggy-back LSD, such as an insert or VC, you have to take the suspension, inter alia, into account, making any general statement -- such as the one Mike objected to -- unwarranted at best. A very well set-up car, in terms of suspension, motor mounts, etc., could go very, very fast on an insert. In contrast, a car with a lousy set-up might be very, very slow even if it had a Quaife.

- Jtoby

ps. yup. still alive and have a better idea: bring the rally car to a winter rallycross and let me drive it!!!

That's the best explination i've read so far and explainis my set up very well. I have MUCH more hp than 300.

I love my insert for straight line acceleration. It definately makes cornering unpredictable, to a point. Therefore I wouldn't suggest it for an INVESTMENT in a circuit track car that should be yeilding financial winnings.

Why I love my insert? I have other specific suspension and drivetrain mods that don't cause the stock differential to bias as "quickly", so the effect of the insert has more profound results. If you can set up your suspension/drivetrain, it should only need a little "encouragement" to maintain equal division of power across the driveshafts. Consequently, since an insert just "encourages" non-biasing, all that would be needed is such an insert when running a straight line. A FWD suspension can be set up to only need that "encouragement" not to bias if you plan on drag racing. An LSD insert is cheap and does this. At rediculous hp levels, perhaps the lsd insert won't "encourage" enough even w/ the proper FWD suspension/drivetrain mods; but I havn't come across this yet w/ my set up.

I don't believe such a suspension goal is possible w/ a rally or curcuit car. OR such a goal would not be as cost effective as just running a true quaife style lsd and the more "run of the mill" suspension mods neccesary to get the most out of the quaife.

BTW, I have a SBR lsd insert. It does great for me in a straight line out of the hole or on MOST turns once i figured out how it changed the way may car cornered. But I don't circuit race nor do I condone speeding in excess on publicly maintained highway curves.

 

[jtmcinder]

Thanks for the kinds words. Let me return the favor by saying, as gently as possible, that I don't think that you understand the concept of "torque bias" very well.

Before starting to explain this, let my try to make the distinction between two different terms as clear as I can for the way that I use them. They sound similar, but they are almost opposites. For more on this, read the white papers by Quaife and Kaaz, assuming that you can find them, which I can't right now.

When talking about an uneven division of torque created by (for example) a planetary differential, I use the term "torque split." The new STi has something like a 41/59 split. The old ones were 35/65. The Cusco Tarmac diff for the Evo III (which, therefore, also fits in our cars) is a 35/65. Note that the torque split produced by a planetary diff applies only when the diff is open. As soon as some piggy-back LSD kicks in, then all bets are off.

In contrast, I use the term "torque bias" to refer to the current, instantaneous division of torque as being used by the two outputs from the diff. If the diff is locked (hard), then the torque bias can be anything from 0/100 to 100/0.

Now, some LSD devices are only capable of locking so much. A Quaife, for example, is usually limited to a 4:1 ratio (i.e., anything from 80/20 to 20/80); the specific limit depends on the angle of the cut of the helicals, since the angle is what determines the side-force on the ends of the pockets, which is what actually causes a Quaife to lock up.

Other LSDs are not limited in terms of a ratio, but are limited in terms of how much torque can be re-routed. The fancy new electronic clutches in Evos and STi have a limit of this sort. The inserts that are available for our cars also have a limit of this type, but I have no idea what it is.

So, what the point here? Well, when you say that an "insert encourages non-biasing" (or something like that; I'm too lazy to check, but I'm sure it's close enough), that is almost the exact opposite to what an insert actually does. Because an insert is always active -- since, as you wrote, it seems to react faster than a VC -- it is always encouraging bias. As soon as one output cannot take any more, the locking of the insert (or, more accurately: the resistance, of the insert, to any difference in outputs speeds) immediately acts to bias torque to the other output.

In other words: yes, an insert interferes with the native torque split of the diff into which it was installed; however, the way that the insert interferes with the split is by biasing torque from the moment you install it.

[My fingers hurt.]

- Jtoby

 

[GSTeclipse]

I had a BM LSD Insert a few years back and I had right at 300whp and the LSD insert failed , putting holes in my casing which allowed metal/aluminum chucks to get into the gears , and well the stock diff was destroyed !

I would never use another LSD insert no matter what ....save your money and buy the real thing even if it takes you a year to do so ...your stock diff is good and I have ran pretty good in the 1/4 with the stock diff in old FWD it ran a 13.0@116mph with
225/50/16" radials tires (not drag radials or slicks)

don't destroy your tranny

 

[dsm-onster]

A note. New phantom grip style inserts use much better springs nowadays.

Also, here's Shep's stage 4 transmission. It's a great unit. I've heard few complaints. Scroll down to the options. He sells LSD inserts separately as well. He's got a HUGE name to maintain.

 

[JrCRXHF]

well the lsd did fine in auto X i have some things to change on the car but i put down the power well. Not that it was alot of power.

I don't know if the LSD made the car do a power on under steer more or not but i did have a problem with that. I am going to change the ride hight and camber along with air pressure to try and fix this problem.