I was under the impression that a torsen LSD (stock on FD?) is superior to a clutch type LSD (KAAZ).


What am I missing here?

 

the problem with the stock torsen unit is that it cant handle a lot of power or hard launching. The Kaaz unit also frees up a few ponys.

 

when is the Kaaz unit normally recommended in the list of mods? or at what hp level?


also I imagine it's needed when changing diff ratios to keep traction?

 

Wheel hop + Torsen diff = exploding diff.

Aftermarket clutch type diff's tend to be harder to break in the FD.

 

It's needed when you are drag racing. The stock diff is very good except it's not built for drag launches. As already stated, wheel hop can kill the stock diff even with little power.

There are products available that help keep the stock diff (and aftermarket ones) from being susceptible to wheel hop like Differential Braces.

 

so even if wheel hop was controlled with a diff brace, toe links and trailing arms a launch on slicks would be unsafe?

what about drag radials?

 

Read my post in your other thread. The FD is just not naturally built for drag racing so there are a few things you need to do to turn it into one.

 

using a diff brace, nylon diff bushings and nylon front longitudinal link bushings along w upgraded rear shocks/springs....

1. will you still get wheel hop
2. will those mods allow the stock torsen to live while drag racing?

can you run w the above setup in the very low 11s, high 10s and maintain the torsen?

thanks,

howard coleman

 

I know the stock diff can take a bunch of tq and abuse cause Hinsons ran the stocker in his LS1 car for a long time with slicks and hard launches. The difference (and what I've always said kills them) is the launching rpms. He was launching around 4K and a high hp single turbo car is going to launch around 6K or higher.

Hinson made TONS of passes and it never busted......UNTIL his very first launch at 6K rpms and it snaped like a twig.

Its a instant jolt from a high rpms launch that kills it

BTW - Hinson was leaving the line with over 500rwtq and had been for quite a while before it broke so I really dont think its the tq that kills them

STEPHEN

 

stephen,

that's very interesting... what mods if any did the car have as far as rear bushings, springs, shocks... i assume he didn't have a diff brace? what tire was he running and approx what et?

it might be possible to run the stock torsen w the right rear suspension mods.... and then again it might not. i might start a new thread to explore that issue..

btw, u going to the rr?

howard coleman

 

simple rules to go by. You have to pay to play. If you want to drag race your FD, you are gonna have to replace the differential either now or later, but it will happen. If you are using drag radials or slicks that is just more of a chance of it breaking. Just replace it and have the peace of mind of not getting stranded at the drag strip or on the street.

 

Of course it's the torque that kills them.

When you shock the drivetrain instantly with a lot of torque by dumping the clutch at higher rpm from a standing start, there are basically three events that can occur...

1. The tires break loose, relieving the strain on the drivetrain
2. If the tires can't break loose, the car moves, relieving the strain
3. Something breaks before either of the first 2 options can take place

If you subject a part to repeated abuse outside its intended operating range, something will give eventually. The weakest link in the FD's drivetrain just happens to be the Torsen differential. As soon as you replace that, though, you'll eventually find the next weakest link. Axles, differential case, U-joints, etc.

That said, the stock Torsen differential will handle a lot of power if it is not asked to do so on drag launches. The "power handling" of the unit goes up considerably if the car is already in motion, or if the tires can break loose to relieve the strain.

 

New question: is the stock torsen better for Autocross and road racing?

I've always been under the impression that torsen diffs are better at distributing torque than clutch diffs

 

Absolutely.

They are.

 

then the stock torsen it is, I don't care much about 1/4 times, at least not as much as handling...

thanks for the help guys

 

The thing I hate about my Kaaz unit is the noise... Before the unit warms up it is loud and sounds terrible. I have LSD additive in it. I totally regret ever getting it. I bought it when I was drag raceing my car and had 4.3 gears installed at the same time. I like the 4.3 gears. BUT once the KAAZ unit warms up it quiets down.

Just my 2 cents

 

All around the Torsen is the best diff. If your putting out 600+HP launching at 9000RPM blah,blah, blah, the Kaaz is probably better. Otherwise, stick with the Torsen.

 

One Wheel Wonder!

 

Interesting, I'd imagine with his wide *** tq curve the tq would be close to the same at 4000rpms as 6000rpms. The alternative is the instant shock of going from 0rpm to high rpms instantly. Also, keep in mind he made prob close t0 50% more tq than 90% of the rotary cars that bust thier diffs, the reason the rotary cars were busting them is cause they were launching at much higher rpms. As soon as he started launching like the rotary cars (high 6000rpms launches) he busted it.

In addition if you look as rotary powered FD, you'll hardly ever see a seq car bust his diff at the track. The reason is they launch at low rpms. Then they convert to seq or single and even with about the same tq all the sudden they bust the diff. The only difference is with the nonseq or single they had to start launching at 6000 to keep from bogging.

You are entitled to your opinion as am I. I've been to the track enough and compared setups enough to form the opinion that its mainly the instand jolt of a high rpm launch that kills it.

STEPHEN

 

Yea, I'm going. I'm in the middle of redoing my fuel system though so I'm not sure if I'll have my car. I might end up riding with a friend but either way I'll be there.

I'll look for ya

STEPHEN

 

with the KAAZ you mean

 

Going to the track a lot doesn't automatically give you an understanding of the Physics and mechanics behind drag racing...

It's the torque that breaks parts. What do you think that jolt is? Twisting force. Torque.

As I stated... either the tires break loose, or the car moves, or something breaks. There are no other options.

 

I was always under the impression that "drag radials" reduced wheel hop (because the sidewalls absorb it). So wouldn't the diff. be less likely to break with them than with low profile stock size/type tires?

On the same sort of reasoning, wouldn't launching at 6000 RPM cause more wheel hop than at a lower RPM, thus increasing the chance of breaking the torsen?

Oh, and Jim, comments I recall from RX-7 drag racers from "several" years ago, the half shafts are next to be broken when you deal with the diff. Yes, there is a "stronger" one available. To quote the racers "it breaks too". Wish I could remember their names. I'm getting too old!

 

Most drag radials don't have enough sidewall to absorb a significant amount of the shock of the launch, even when aired down. A true "wrinkle wall" or bias-ply slick is the best way to keep from immediately breaking parts while drag racing, although of course there are no guarantees. A lot of people have used the M&H Racemaster P305 DOT slicks (prior to the availability of Mickey Thompson ET Street slicks) with good results because of their ample sidewall.

Switching to an automatic transmission is the next best way to preserve your drivetrain while drag racing. Manual transmissions are notoriously much harder on drivetrain components.

I listed axles first following the differential.

I talked extensively with Ari Yallon about what he'd broken and how before I started in on improving the rear of my car.

Ari was breaking the 300M chromemoly axles that RP sells, so he had a few pairs of 350M axles made. Once he wasn't breaking the axles any more, the inner CV joint cups started to let go. Cryo-treating them improved their longevity from about 3 passes to several races, he said. I never did find out what the next link in the chain was because at that point I decided to go with a different differential entirely. He did say that he'd done extensive welding on his differential case to strengthen it, however, so I assume that he's cracked at least one open in the past.

 

Very interesting, because I experience the exact opposite. My Kaaz makes a lot of noise when it's warmed up and I always use Kaaz LSD oil.

I strongly suggest to stay away from the Kaaz, I seriously regret getting this mod.