TailHappy

I just put a 1.5-way KAAZ in my car since I blew up my last Torsen. From all I had read, the KAAZ was suppose to be the **** for racing. However, my first impressions are very contrary. First, let me preface everything by saying that I replaced the trailing and toe links at the same time, and I haven't gotten a chance to have the car re-aligned yet, so maybe that's part of the problem...

However, what I've noticed so far is that the car seems to want to understeer horribly when the KAAZ is locked, and then as soon as you let off enough to hear the telltale click that it has unlocked, the car swerves into the turn drastically. With the Torsen, I had taken a driving style of getting into the gas early coming out of a corner to help stabilize everything. However, if I drive the same way with the KAAZ, I'm going ot be pushing off the outside of the track. But this thing IS supposed to be better/faster, right???

So what fundamental changes do you guys recommend? Waiting later to get on the gas? Giving more gas so that the wheels are slipping and helping the car to turn? That'd definitely be the fun way but doesn't seem optimal if I want my tires to last and entire session...

Or might this all just go away once I get an alignment?

APEXL8T

Alignment is foremost...then look at things. Yes some suttle difference...your OE may not have been as hooked up as much as you thought and you learned to drive your line as such.
Push that much may need suspension mods to correct but thats after you resolve the alignment.

TailHappy

Thanks for the reply. I'll hold off with worrying about it until I get a 4 wheel alignment, then. I was just surprised at the marked understeer when the diff is locked. Was hoping that wasn't due to the KAAZ....

DamonB

It is due to the KAAZ. Once any diff is locked the axles are turning at the same speed and this will always promote understeer since the inside and outside drive wheels cannot rotate through the corner at different speeds. Alignment is not going to fix this.

A Torsen loads much more progressively and doesn't completely lock, a KAAZ goes from a functional diff to *click* 100% locked. You're not imagining things between the two diffs; your impressions are 100% correct. People switch to the KAAZ because they have the power to break the Torsen. If you're not breaking stock diffs I wouldn't use a KAAZ for road racing.

In order to cure the understeer problem you're going to have to get more of your turn in done with the diff unlocked and be patient before getting hard on the gas because if you power it too early before the car has rotated through the corner you're going to go off the outside. This means you're going to have to turn in earlier but in a straighter line towards the apex, brake hard and lift while getting all your turning right around the apex done in a very short time and then back on the power hard. The idea is to spend as little time as possible off the gas with the steering turned and it would essentially be like the parabolic line.

Unless you're making huge amounts of power and having problems with wheelspin on corner exit I see no reason to trade the Torsen for the KAAZ. The KAAZ is physically stronger and so works great for drag racing in a straight line when you drop the clutch from high rpm but road racing with any 100% locking diff will create problems just as you've encountered. A locked diff will insist you have to be willing to rotate the tail of the car in order to turn and that means braking very late and very hard and pitching the car into the apex while letting the lightly loaded rear tires to slide a little to turn the car. Contrary to popular belief a Torsen doesn't lock (neither does a clutch type diff).

TailHappy

Thanks for the good reply, DamonB. Well crap, that's what I was afriad of, and that's the way I had imagined it in my head; the inside wheel pushing too hard and preventing good cornering. What I didn't understand is that in my limited research before buying the KAAZ, it seemed like people were saying good things about it for both road racing, drag racing, and drifting. Went with a 1.5-way with about 70% lockup. Definitely didn't expect such a marked decrease in cornering ability.

Which leaves a real delima. Not only is it adversely affecting cornering ability, it's also an aggrivation in my day-to-day driving. But on the other hand, I have already blown out a torsen while drag racing, and my strategy has always been that if I break it and have to fix it, replace it with something stronger.......

Anyway, thanks again for the responses. Guess I'll keep my old torsen around after all...

Carl Byck

So basicly as it was explained to me by a road race guy, properly driven, and with sufficent power a locking diff is faster, but you have to adapt your driving style, and you will go through tires alot faster. Kinda like driving on Hoosiers, not for the amateur, or the budget impaired

TailHappy

Speaking of, it is truly faster in a straight line, correct? I thought I had read that the power losses were less on it than on a torsen, thanks to less gear losses.

DamonB

The key again being if you have enough power to have traction problems at exit. If you don't have traction problems you don't need a locking diff.

TailHappy

I'm fortunate enough to have traction problems, though I don't call that a "problem"

I'm just talking in theory now, but do you truly get more traction with a KAAZ? It almost seems to me that if it's trying to spin both wheels at the same speed, and you're trying to turn, you're overusing one tire, and underutilizing the other. I don't think big powerslides are the optimal way of racing, though it's definitely optimal for fun....

Oh well, regardless, at least it's one less thing I have to worry about breaking...

DamonB

Just like anything else it's a compromise. The locking diff is going to give up a little driveability immediately around the apex but it will do a better job of putting the power down when the car begins to head towards straight (again with the big disclaimer being if you don't have this problem you have no need to try and solve it!).

Unless forced by rule (Trans Am and NASCAR on roadcourses for instance) nobody uses a true locking diff that I know of; it's always a form of limited slip. Locking diff designs tend to be cheap and robust, not better performers. As the diff cycles from one wheel drive to two wheel drive (and keep in mind this happens instantly) the car will of course move around and you have to fight the adverse yaw. A true limited slip (whether Torsen, Weisman, clutch pack etc) is a better solution but these are more complex and expensive. To the best of my knowledge modern F1 diffs and those of most top level road racing classes are essentially Weismans.

Trans Am and NASCAR (only on roadcourses) mandate locker diffs because of cost. Neither series wants teams dumping money into diff research and would rather the diffs stay simple, cheap and "stupid".

TailHappy

Great responses, thanks DamonB.

particleeffect

what is a Weisman diff? i've spet like 20 mins looking google, found nothing.

macdaddy

Weismann (Costa Mesa, CA) makes transmissions, transaxles and differentials for a variety of high-performance applications. http://www.weismann.net/

DamonB

Sorry, I left off an "n". It's "Weismann". The mechanical function of a Weismann type diff is somewhat similar to a cam and pawl but the Weismann uses caged rollers against an inner and outer set of cams rather than the "chiclets" of a cam and pawl. The operation of the Weismann type is more progressive, quieter, smoother, cooler and doesn't wear as quickly compared to the ratcheting action of a cam and pawl. I believe a Kaaz is just a cam and pawl diff.

http://patft.uspto.gov/netacgi/nph-P...y=PN%2F4817451

Clutch pack type diffs are commonly called "Salisbury" types. I need to correct myself earlier when I said to the best of my knowledge most top level organizations are running Weismann type designs. There are some that do but they are far outweighed by the Salisbury users because it is so much easier to adjust the torque bias of the clutches in the Salisbury. Sorry for getting my proper nouns mixed up.

Some discussion of other diff types here

RX-Heven

iTrader: (1)

Can't the Kaaz diffs be retuned by removing some discs to make them more suitable for road racing than the 'out of the box' setup?

TailHappy

Yep, you can reverse the clutch plates to adjust the % lockup. Mine should be down in the 75% range, but it's still pretty harsh..... Finally starting to get used to it though.

concept-R

You going to continue working with the KAAZ? Id appreciate more impressions as you go along. My personal experience has been with Torsens and Ive found the controlability to be quite good and predictable.

I am considering going with an FD torsen while I save up for a guru.

TailHappy

Yeah, I'm probably going to stick with the KAAZ. I've about gotten used to its harshness in daily driving and changed my driving style accordingly. I'd be hard pressed to decide between two if the torsen was stronger than it is, but since I already grenaded one of those, I really don't want to do a second one.... (though I AM keeping an old one on hand just in case I change my mind...)

I'm still undecided on the performance difference of the KAAZ. Feels like I may have a tad more power, but it's minimal enough it might just be my imagination. I originally didn't like the way it causes so much understeer under power, but that may end up being a confidence-inspiring thing. Too early to say. Haven't been able to get back to the track since I installed it. But it IS a ball doing powerslides with this thing!

I'd say for anybody considering one, it'd be worth your time to find someone that already has one installed, and either take a ride or drive before buying one...

T_Racer

iTrader: (1)

As far as tuning it and adjusting to the new diff, you should read the Sport Compact Car Project 350Z. They added a Kaaz and had it set at like 75-80% at first too. They commented that it still made a push in the car that wasn't there before, and took a good long break in to let it seat in. I am not remembering verbatum, but the long and short of it is that they too had to tune down the diff to make a difference. They took it apart and showed the internals and how the changing of the diff plates made a difference in the lockup of the diff. IIRC, they ended up with like 40-50% lockup with remarkable turnin compared to out of the box after playing with it. One specific comment was as a baseline before tweaking the diff, that turn-in was horrible, with a bad push through the whole corner, ala stock settings like a locked diff = trying to go straight. This was over two installments, and unfortunately, cannot remember the issues that this was in, but usually online.
In a nutshell, though not easy, may take a test and tune, though, this could eat up a day just changing twice. I would ask around a little more or see if someone has a setup solution.
However like Damon was saying, the only reason they went to this one was with the BFG KDs and larger footprint, along with a little more power, doing peg leg burnouts. They commented that the stock diff was getting the job done, as long as it was in stock form. Hope this helps, just my .03 ( my .02 adjusted for inflation)

Cheers,
Travis

concept-R

I guess with the car tending to push towards the corner, this set-up might be good for drifting...lol.

Out of curiosity, how much hp/tq are you pushing that you are blowing torsens?

TailHappy

Thanks for the info T Racer. Definitely good to know, but I'm not sure for my needs I'm going to be all that antsy to go pulling it back out again. BOY that was a PITA, at least in MY lazy opinion... But next time it's out, I may consider swapping a few more plates.

I don't have any tremendous amount of power, conceptR. Currently running right around 360rwhp, though as soon as I get bigger injectors I'll be turning up the boost some more. Problem was trying to drag race, got some very nasty wheel hop, and before I could get back out of it I had snapped some teeth in the torsen. I just am the type that only likes to break things once, so if I'm gonna have to replace it, I'm gonna make it stronger so it doesn't happen again! Plus, I orignally was under the impression that a KAAZ would be better and more predictable on the track...

concept-R

lol, I can understand your concerns about breaking another torsen. All things equal, a KAAZ can blow up too depending on the situation. Have you considered shoring up your bushings out back to help prevent wheel hop?

In any event, I like the predictability of a torsen style diff and I, too, am very much concerned about longevity. Ive been looking into Guru's offering. It's a bit on the expensive side (dunno how it compares price-wise to KAAZ diffs) but Ive heard good things about its strength.

I should have one in my seven near mid-spring, just in time for AX/track days.

TailHappy

Yep, I've been trying my best to rid the car of wheel hop. I replaced all the pillow bushings, put in HD diff mounts, and did the upgraded trailing and toe link bars. Helped, but I still get wheel hop sometimes...

I probably should have done better research before I bought my KAAZ. I got a good deal on it used, but at the time I had never seen the guru one mentioned. That might be the way to go.

I actually think the KAAZ is probably a little more predictable than the Torsen, but I think the torsen would help you turn better, especially in autcrossing since the turns are usually so sharp. The KAAZ will probably be fine for the track though. Mine starts grabbing and noticibly shaking the car about at about 1/2 turn of the wheel, if you're not cornering hard enough for the wheels to be slipping.

RoadRaceJosh

Wow, that's a tight diff if it's shaking the car around corners. I'm used to clutch type LSDs that make no noise, let the car turn, and burn both tires under power. Can I assume you used the friction modifier in the gear oil?

Joshua

TailHappy

My sentiments exactly. I've driven Mustangs and Dakota RT's that both have clutch LSDs and they don't act like this at all. I imagine they're tuned down to slip a lot more, though. And yes, I added the friction modifier. Put that in as I was installing it, so I can only assume it helped...