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Discussion Starter #1
Hello gang!

What is the final word on if LSDs (clutch pack or Torsen) are a worthwhile change for us naturally aspirated powered track rats?

A little background on my car:

-2005 Lotus Elise
-Naturally aspirated, 177whp, 124ft-lbs
-2-way Penskes
-BWR SCCA front anti-roll bar
-big rear wing and front splitter
-Hoosier A7s on cute 15" Miata 15x8" wheels
-Kaaz close ratio gearset
-Stock open differential

This weekend at the NASA Nationals, I finally got down to a 1:34.6 on the Mid-Ohio Pro-course configuration. A new problem arose...

Inside rear wheelspin in the keyhole, exit of T4, exit of T6, and entrance to T9 (thunder valley). I've never experienced this before, and I'm absolutely positive it's because my cornering speeds have increased so much this year. This happened to me in a few spots at Pitt Race too this year after yet again reaching a personal best hauling ass in the corners.

With that said, I know I'm leaving time on the table when my right foot is flat on the gas, and I have wheelspin. Being an engineer, I know that this could be addressed with a different differential. But, I've heard that it isn't exactly ideal in various discussions.

Can anybody elaborate on their experiences with various LSDs in their cars? It seems to me the clutch-type LSD would be ideal for this car, but I'd really like to hear everyone's opinion.
 

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@fzust might be able to offer some advice and was very helpful when my transmission needed rebuilt.

If you're experiencing wheel spin I think it is time to get the LSD unless that is breaking some rules in your class. I have not had issue with my stock LSD on track but if starting from scratch I do not know what version of LSD would be best for you.
 

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Discussion Starter #7
Are you spinning the inside because it is unloading completely or?
I have the same suspension as you, Penske doubles, and probably set it up similarly. The issue is the inside rear wheel is going over the slippery paint on the apex curbing when my right foot is fully on the gas, and then that wheel spins. I try and avoid launching my car like a rocketship over really rough curbing, but the curbing at Mid-Ohio is very forgiving.
 

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My vote is always for Torsen. A clutch pack will induce understeer on corner entry. A Torsen is seamless as long as you keep the wheels on the ground.
 

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Here is a video at Pitt Race that shows the inside wheelspin slightly occurring in T5 and REALLY smoking it up in T17.
Can you identify what time on the video Turn 5 and 17 are as I'm not familiar with that track? Want to make sure I'm not just mistaking sliding for what you think is wheel spin.
 

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Discussion Starter #12
Can you identify what time on the video Turn 5 and 17 are as I'm not familiar with that track? Want to make sure I'm not just mistaking sliding for what you think is wheel spin.
0:43 is T5
1:47 is T17

Wish I had a sweet AIM smartycam with overlaid data, but this is all I have!
 

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Although an Elige can be setup without an LSD, done correctly, an LSD is a fine addition.

As far as Phil's car goes, it had a BWR SPEC OS Giken for a while and I think he went back to open diff. The reasoning is pretty simple: He ran a sequential transmission with Redline Shockproof heavy gear oil. That stuff is so slippery that it effectively disables the OS Giken! How do I know? I borrowed Phil's gearbox for nationals after mine broke, it had zero lockup, and one-wheeled everywhere! I later tested it on the bench and it had very little lockup. If you use that gear oil in a synchro box you will destroy it. Last but not least, Phil was able to make that setup work with Big Rubber, Bigger Aero, and the stiffest springs I've ever seen used on an Elise. He needed the springs for the big aero for platform control but the benefit is everything was quite planted. I am sure in tight corners there was some inside wheelspin anyway.

OK now that that is out of the way, the easy button is the Quaife LSD or the TRD. I like the Quaife better as it is a bit tighter and has a bit more preload. Both of these differentials are torsen type and are effectively open on corner entry. They turn-in great.

The only experience I have with Cusco Differentials is pulling the broken bits out of gearboxes.

The 100% best differential barr-none is the BWR Spec OS Giken. It is special order only from us. Here's the true skinny: The OS Giken Diff is tough as nails and I have used one on the XP car for years. I spent alot of time working with OS Giken doing a special setup to fix corner entry push and the engagement ramp to maximize thrust out of corners. The downsides are cost and because it works so well, it is tough on transmissions. If someone wants to go that direction, I recommend having a spare gearbox.

If anyone needs a Quaife, we are a dealer and have alot of experience building gearboxes for these cars.
 

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AH, I also noticed that the OP is running the KAAZ gearset, so actual torque is a good bit higher than regular NA due to gear reduction.....
 

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Very nice driving.

The OSG is a great part especially with race slicks. I sold mine this summer with a BOE 400 motor, I found it touchy on decelerations with street tires. I will admit I don’t change my alignment with different wheel/tires so the amount of traction is greatly reduced with street tires and race camber and I think the OSG works better after it’s broken in. I ran an OSG on my NSX for years and like Fred says, they are super tough. I found DuMondeTech Gear 9 works great with it, the diff is a bit louder, but lock up is smooth and the lube is easy on clutch pack, bearings and synchros.

I have become a fan of the Torson diff, it works great as long as you are comfortable with trail braking. A Torson will spin the inside wheel if the tire is ‘completely’ unweighted, like over tall rumble strips. The diff only needs the slightest resistance on both wheel to work correctly and that can be the lightest bit of brake being applied. I drive a car with a Torson a bit more with the brake pedal and throttle, stay on the brakes later until AFTER I’m on maintenance throttle mid corner and often through the apex of the turn. I have charged the way I use my left foot to become more gentle with the pedal so I can feather the brake off as I roll throttle on.

I would suggest you see if you can test drive either diff set up before you buy. See if you can get a little seat time in any LSDin an Elise.

Keep going fast!
 

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Those videos are some next level stuff.

From my little bit of experience it seems in T17 the change in pavement caused the excessive wheel spin.

With an NA powered car, I would be more concerned with lost time due to understeer. With that AIM can you plot RPM vs vehicle speed to calculate actual time/ MPH being lost?

I'm like 13 seconds slower than you in an 06 NA. So take that in mind... HAHA
 

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Discussion Starter #19
Those videos are some next level stuff.

From my little bit of experience it seems in T17 the change in pavement caused the excessive wheel spin.

With an NA powered car, I would be more concerned with lost time due to understeer. With that AIM can you plot RPM vs vehicle speed to calculate actual time/ MPH being lost?

I'm like 13 seconds slower than you in an 06 NA. So take that in mind... HAHA
Is this Red Rob?

With a stock engine setup, we have to do the basics better than everyone else. Every inch of track counts!

With the AIM Solo DL model you can plot RPM vs vehicle speed. I am using an original AIM Solo, so it doesn't have the capability of logging any parameters over OBD2. The ideal logging strategy would be to check individual wheel speed sensors, create a comparison, and then make conclusions on the need for a LSD. But that's multiple thousands of dollars more than my AIM Solo!
 

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No, it's not.

Do you still run ABS? You could use the factory wheel speed sensors. There is a post on here of someone hacking the ECU. It's basic stuff if someone is willing to spend time to map the pins from the sensors into the ECU.
 
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