Differential Preference for Rally/Rallycross?

[Philld_with_donuts]

Hello Everyone!

I've read through quite a few threads and websites talking about the advantages of the various types of differentials available for our vehicles, but was wondering if anyone had any experience using any particular one for rally/rallycross?

I want to pull the trigger in the next few days on a differential and try to get it installed before my next race on Aug 29th.
What does everyone think would work best on low friction surfaces?

o The MFactory unit is the cheapest option, and installation looks (relatively) easy, but instances where I have one wheel up may be an issue. (Split mu also?)

o The Quaife ATB is used in the Team O'neill cars, and I have the hook up on getting those for a little less than the current sale on Mountune, but think having one wheel up would still be an issue. (Split mu also?)

o The WaveTrac seems highly recommended, and the functionality seems to avoid the wheel up torque loss... a little more expensive than the Quaife, and shims required for install.

o Then the Kaaz 1.5 way clutch type seems like the best choice as it can be dialed for the most true "lock" under acceleration, and maintains that lock irregardless of wheels in the air. But no one ever seems to use them or talk about them? Am I missing some detriment about them? (Aside from the maintainance of needing to change fluid every so often?) There is also no break in period required if I opt for the "SuperQ", whatever that is. This is also the most expensive option, but best performance is the ultimate goal here.


FYI - My car is not daily driven and sees 99.95% of it's life getting beaten on at rallycross events. The other 0.05% is the occasional open track day.

Also, major noob question - I leave two distinct tire tracks on the ground when I burnout, but I can rest assured that a lsd was never installed in my car because my front wheels spin opposite when the car is jacked up... right?
I'd hate to get everything out just to find a diff already there. lol



TLDR: What diff should I use for rallycross?




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[M-Sport fan]

How often is one wheel up in the air at your local rallycrosses, and over the curbing at your track?
The KAAZ is a clutch plate type diff so it will need maintenance over it's lifetime, and it will wear, most likely quicker than any of the Torsen type worm gear diffs, as well as needing a limited slip friction modifier additive () in order to function properly, but yes, it may also provide the best outright lockup.

I do not rallycross, and do not plan to in the foreseeable future, but I DO have to drive on bad gravel roads, so I will go with the Wavetrac if it is still around when I am able to install a limited slip diff.

 

[Philld_with_donuts]

How often is one wheel up in the air at your local rallycrosses, and over the curbing at your track?
The KAAZ is a clutch plate type diff so it will need maintenance over it's lifetime, and it will wear, most likely quicker than any of the Torsen type worm gear diffs, as well as needing a limited slip friction modifier additive () in order to function properly, but yes, it may also provide the best outright lockup.

I do not rallycross, and do not plan to in the foreseeable future, but I DO have to drive on bad gravel roads, so I will go with the Wavetrac if it is still around when I am able to install a limited slip diff.

This is certainly the moment I wish I had the photo from this weekend where (we'll call it) one wheel was about a foot in the air

But to your point, tracks like that aren't common. Typically the friction is so low you aren't lifting one wheel from chassis rigidity like you might in other scenarios.
I always wondered what was happening though when going over very rough surfaces or kicker-like bumps... I would assume those have to momentarily freespin a wheel, and feared that would screw with the torque as it tries to bias from side to side...

I really want the diff to help me get going from a start where I just sit planted digging holes in the ground, and also to help pull me out of very sandy sharp corners. These two places are where I seem to be losing a lot of time.

 

[M-Sport fan]

@JDG hopefully will come in here and give his suggestions as well, since he seems to be the most active/into it rallycrosser on here currently.

At the one event I was spectating at, where he was driving, A LOT of the 2WD (front or RWD, but more so the higher powered FWDs) had MAJOR troubles getting off the line at the start (even those with REAL rally gravel tires albeit yes, they do help a bunch), especially once that area gets dug up and heavily rutted.
(Like everyone using their rev limiter as a de facto traction control, type trouble getting going!)

I notice this even more when working the starts of actual ARA stage rallies for the open class FWD cars, given the higher power of most of those cars, even with a limited slip diff.

Of course the AWD open class 'supercars', R5s, etc. launch like nobody's business, even in those lousy start conditions, given the grip they have with top tier tires for the conditions, launch control/2 steps, and adjustable center diffs, and possibly lockable axle diffs, etc.

What some must do to get off of the line (especially on stages that are run more than once the same exact way/direction, so same start line/area) is go way over to one side or the other to avoid the loose, dug up soil and rocks, and try to get going on somewhat 'fresh' ground.
Sometimes they are launching with their front wheels about a foot away from my legs! LOL

 

[Philld_with_donuts]

@JDG hopefully will come in here and give his suggestions as well, since he seems to be the most active/into it rallycrosser on here currently.

At the one event I was spectating at, where he was driving, A LOT of the 2WD (front or RWD, but more so the higher powered FWDs) had MAJOR troubles getting off the line at the start (even those with REAL rally gravel tires albeit yes, they do help a bunch), especially once that area gets dug up and heavily rutted.
(Like everyone riding the rev limiter type trouble getting going!)

I notice this even more when working the starts of actual ARA stage rallies for the FWD cars, given the higher power of most of those cars, even with a limited slip diff.

Of course the AWD open class 'supercars', R5s, etc. launch like nobody's business, even in those lousy start conditions, given the grip they have with top tier tires for the conditions, launch control/2 steps, and adjustable center diffs, and possibly lockable axle diffs, etc.

What some must do to get off of the line (especially on stages that are run more than once the same exact way/direction, so same start line/area) is go way over to one side or the other to avoid the loose, dug up soil and rocks, and try to get going on somewhat 'fresh' ground.
Sometimes they are launching with their front wheels about a foot away from my legs! LOL

Yeah I had started styling this question in JDG’s build thread, but figured I shouldn’t hijack his thread.. I’m sure he’ll chime in eventually.

I do run MRF ZDM3’s but most my region runs gravels or mud tires also, so that start line get obliterated pretty fast.
That’s awesome you get to work some of the stage events. I’m hoping to start the ARA registration process next year. I’m feeling cautiously confident after two full seasons of rallycross.

 

[Fusion Works]

Lincoln locker. Just pop out the stock diff and weld the spider gears solid. It will suck at low speeds in the paddock as it tries to break your hands when you turn, but on course it will be magic. You will probably break axles next. HAHA. I did one for a rally cross VW jetta many years ago. It was violent in the parking lot, but the owner said it was magic on the dirt.

That said. Plate type is my choice for my road race cars. Simply because of the possibility of lifting a wheel and it going open. I am currently using 1.0way Mfactory metal plate diffs that I modified for increased preload. You don't want the 1.5way for a FWD car as it will upset the platform under braking with split Mu surfaces.

What do you do for FCA?

 

[Philld_with_donuts]

Lincoln locker. Just pop out the stock diff and weld the spider gears solid. It will suck at low speeds in the paddock as it tries to break your hands when you turn, but on course it will be magic. You will probably break axles next. HAHA. I did one for a rally cross VW jetta many years ago. It was violent in the parking lot, but the owner said it was magic on the dirt.

That said. Plate type is my choice for my road race cars. Simply because of the possibility of lifting a wheel and it going open. I am currently using 1.0way Mfactory metal plate diffs that I modified for increased preload. You don't want the 1.5way for a FWD car as it will upset the platform under braking with split Mu surfaces.

What do you do for FCA?

"Break your hands when you turn" / "Violent in the parking lot" Sounds like my kind of party.

Lots of the fast guys are running lincoln lockers. I might have to trade cars with one for a run just to see what the hype is about.
It's certainly an option! I do have a welder

And at FCA I started in SRT Powertrain, then jumped ship to work on cooling systems for Jeep Wrangler. Now I design the turbocharger for the 2.0L in the Jeep and Alfa vehicles.

 

[Fusion Works]

Cool. So you were involved in this:
https://jalopnik.com/the-engineering-behind-the-jeep-gladiators-tow-rating-1833657453

 

[Philld_with_donuts]

Cool. So you were involved in this:
https://jalopnik.com/the-engineering-behind-the-jeep-gladiators-tow-rating-1833657453

Unfortunately I am not that cool. I faced many challenges trying to cool the 2.0L in the Wrangler, but nothing press worthy.

My first project at FCA was this though.. and this was crazy fun:
https://www.motortrend.com/news/talking-trackhawk-with-a-jeep-srt-engineer/

 

[Fusion Works]

Ludicrous. We should talk more off line. HAHA.

 

[M-Sport fan]

Lincoln locker. Just pop out the stock diff and weld the spider gears solid. It will suck at low speeds in the paddock as it tries to break your hands when you turn, but on course it will be magic. You will probably break axles next. HAHA. I did one for a rally cross VW jetta many years ago. It was violent in the parking lot, but the owner said it was magic on the dirt.

^^THIS is exactly what a lot of the crews piloting the original rally prepped, Production and Production GT class GLH/GLHS Shelby Omnis, competing in the SCCA Pro Rally events, did way back in the day.

In fact another (former) Mopar engineer, Doug Sheperd (currently the head of the ARA) piloted one of those with that mod way back in the mid '80s, as well as Shadows, Daytonas and some GLHS Chargers as well.

 

[oddracing]

Just wanted to give my 2 cents here, even though this thread is a bit old. That way in case anyone searches for them they can find it!

We had a KAAZ in one of the ST rally cars we built and it completely blew after 2 miles of testing. The spider gears exploded. I worked with Kaaz technical department and they said they haven't had good luck with these diffs, with lots of rally/rallycross people having terminal damage. They DO NOT recommend it for this type of usage. We are currently looking for another solution, because there is nothing better than a clutch style diff for rally. Next on our list is 3J, but I am waiting to hear back from them.

 

[M-Sport fan]

Isn't the Drexler a clutch type diff as well?

Has anyone tried using these for gravel rally apps, or don't they even make one for the IB6 gearbox at all?

Does Sadev actually manufacture the (clutch plate type) diff in it's 5 speed sequential box for these cars, or is it made by someone else?

 

[oddracing]

Isn't the Drexler a clutch type diff as well?

Has anyone tried using these for gravel rally apps, or don't they even make one for the IB6 gearbox at all?

Does Sadev actually manufacture the (clutch plate type) diff in it's 5 speed sequential box for these cars, or is it made by someone else?

Drexler doesn't make an IB6 diff I believe.

I am not sure if Sadev actually makes their own diffs, but I wouldn't be surprised if they do. They already manufacture everything related to the gear box themselves.

 

[Philld_with_donuts]

Just wanted to give my 2 cents here, even though this thread is a bit old. That way in case anyone searches for them they can find it!

We had a KAAZ in one of the ST rally cars we built and it completely blew after 2 miles of testing. The spider gears exploded. I worked with Kaaz technical department and they said they haven't had good luck with these diffs, with lots of rally/rallycross people having terminal damage. They DO NOT recommend it for this type of usage. We are currently looking for another solution, because there is nothing better than a clutch style diff for rally. Next on our list is 3J, but I am waiting to hear back from them.

This is great advice to add! Glad I didn't go Kaaz for mine.

I ended up finding a smoking deal on a Quaife and should have it in soon!