The 510 Realm

Or any other rally type guys. I'm looking to shim up my LSD for my ice race car. I'm guessing that I should set the break away torque higher than the current 35 lbs. I've always run a welded diff in the ice racer, so this is new to me with the LSD this year. I've yet to be on the ice with it,(going in two weeks) but I was driving around this week on Yokohama gravel tires on the street, and it was fairly easy to get the inside wheel spinning. I know there is more traction on wet pavement than on ice, but I don't think the diff is shimmed up enough. The diff is an R190 with 4:44 gears; power is LZ 2.2 producing about 130 or so HP, but fairly good torque.
Any ideas on what the diff should be set to anyone?

Byron

Hi Byron,
My diff is set to about 50 lbs, for what that is worth. If you are spinning the tire at that setting, I do not think you would be too out of line to get close to this.

Hi Byron,
I believe the factory spec was 43 lbs.
So Keith is pretty close.
My preference was for 70lbs with the 2 way.
Better control on light throttle without having to "shock" load the diff to
lock it fully.
Check that the ramps are still smooth.
Baz

That was kind of our theory also, Baz. When we put the really sticky slicks on for slaloming, we wanted the transition on corner exit to be relatively smooth at that part throttle point, minimizing more understeer. I am pulling my diff out this winter just to see how it is all doing in there.

You know, I've never disassembled an LSD - so I'm in new territory. I'm told you can shim the clutch pack to make it a bit stiffer, but how much shim do I start with? .005", .010", .020??? I guess this will be a bit of an experiment. I don't want it to be shimmed up to tight, as I'll be on a slippery surface, and I'd like to keep the turn in under control. I've already got a locker, and I don't want to go that far with the LSD.

Byron

Byron510 wrote:You know, I've never disassembled an LSD - so I'm in new territory. I'm told you can shim the clutch pack to make it a bit stiffer, but how much shim do I start with? .005", .010", .020??? I guess this will be a bit of an experiment.
Byron

I think you are right, it is a "trial and error" exercise - I have never seen a formula for shim width to break away torque. Probably because there are a lot of variables (condition of disks, type of gear oil used, etc.). First come up with a way to take a measurement of what you have now so you have a baseline reading to start with - then make a change and recheck it. Otherwise, you are just taking stabs in the dark and your likely to get all messed up.

I was just reading through the Original copy of the Bible (How to Hotrod and race your 510,610,240Z) and it started that .030" in a R190 with 4:44 gears (what I've got conveniently enough), and their net result was 90 Lbs break away. I'll start with .010", and go from there.

Byron

For the enlightenment of all, I took a bunch of photos in the process of shimming up the LSD. Break away torque started at 27 LBS. For each pair of .005"
shims (one on each end of the clutch pack), about 11 lbs of torque was gained. So I added .010" to each side in the end. A consistent 49 LBS of torque was achieved - just what I was searching for.
Thanks to Baz and Keith for getting back to me with some specs.

Byron

More pics

I think you will find that setting very good for most situations.

Byron!!! Well I haven't checked the breakaway torque on the R190 I installed yet but it did great on the track in the rain so I'm not in a hurry to adjust anything.

I was wondering how does the LSD breakaway work exactly? We put a H165 LSD in Sam's wagon, it didn't seem to work so we swapped in the other one we got (we scored 2 of them) it had the same issue. One thing we didn't think about till after the race, was that the coilovers we put in the back to increase the spring rate don't allow any droop. Yes we know its bad but the reason we installed those is another story. So my question is..... If one wheel lifts does the LSD not really work? Does the tire off the ground get full power and the other tire only gets 45lbs of torque?

Here is a nice page explaining it all.
http://www.ppi-ats.com/LSD/LSD_basics.html

That’s a good article Norm.

Jeff, the last paragraph addresses your question. Break away torque on the bench from one side to the other gives you a mark to gauge and work from, but the actual breakaway measurement when considering the parameters of the drivetrain and wheel diameter is measured in percentage of lock. I’m unsure how this could be calculated as the gear ratio itself would change this reading, as would the diameter of the tire. I would think that placing the torque wrench on the diff input and locking one side of the diff would give you the actual breakaway torque required from the drive line to operate the LSD through the differential itself. But again the tire size would change the actual reading between the diff input and the tire on the ground as it’s diameter would certainly change the applied torque to the ground. A quick reference to this is that Jamie picked up nearly 20hp on the dyno by dropping from his 23 1/2” tall 15” wheels to his 20” tall 13” race slicks.
Maybe someone out there can piece this together But for now it would be interesting to note what your actual breakaway torque is Jeff. It’s a good benchmark to move forward from.

Byron

Just as a comment, for what it is worth, I hate the "lag" on my G35 with the VSLD. There is a most and disconcerting time lag from when you jump on the throttle, to when the car actually reacts to the diff locking up.

As I can drive both cars, my 510 and the G35 back to back, I see it right away. The 510 reacts right away, but with the G, there is a moment where the rear feels like it is going to step out from under me....THEN...it plants the rear end.

If there was a choice for a 510 IMO, I would try to put a conventional LSD in there.

Here is a question for you guys. What is better a high or low breakaway torque? From what I am reading low is better for low speed partial throttle. Ramp up to locking is important and lock % also. I have a choice between 2 LSD's. 1 has low initial and one has high. The low one has a much longer service interval and everything else is the same. They both have adjustable lock % and ramp up. They can also both be set to 1.5 way or 2 way.