Jim Calandrella

Man, I'm sorry to hear about your dif.
I'm possibly in ther same position. I'm interested in the Kaaz, and have some of the same questions about it. I'm not sure what I want to do. I don't want to give up any serious top end just to get down the 1/4 faster. I also don't want to lose any handling.
If I hear anything about it, i'll let you know. Until I know for sure, i'm leaning towards a used stock one for now.
Jim

LT1-7

I don't think the Kaaz rear end comes with a change in the gearing, someone correct me if I'm wrong. I was thinking of getting this rear so if you want to buy my stock rear, let me know. I'll give it to you for a good deal

rotaryextreme

iTrader: (2)

Your rear end is consisted of two parts:

1. ring and pinion
2. LSD

They are two different things. KAAZ makes the clutch type LSD, not the 4.33 ring and pinion. 4.33 ring and pinion is actually a JDM mazda unit used on some of the the 96+ RX-7. If youw ant to go crazy, you can even get a 4.7 ring and pinion. What's broken on your rear end anyways? LSD or ring and pinion?

Chuck Huang

jimlab

Chuck's right, the Kaaz differential does not come with a new gear set. You install it in place of the stock Torsen differential unit, using your old ring gear (4.10:1).

While we're on the subject, I have a perfect OEM Torsen differential with just over 13,000 miles of use on it available. E-mail me (jimlab@earthlink.net) if you're interested, and I'll send you pictures.

7-sins

Sucks to hear it... I watched RedFD go through a stock diff at the track. He tore out a couple teeth on his spider gears... I think those are the same ones you are referring to as well. He installed the Cusco 2-way LSD and it is tight. The tires sometimes chirp while turning, if the back bins and trunk carpet are out you can hear a little whining, other than that its pretty quiet. I think the install was pretty straight forward they didn't change the ring and pinion though. I think that when doing that you really have to get into the shims and crap.

7-sins

You can always get some different size tires to balance out the spedo difference....

jimlab

That's pretty much the "new in box" price, so you're not getting much of a deal, and 4.33s aren't worth a lot where acceleration is concerned.

Here's an example (simulated using Car Test 2000)...

RX-7 w/~320 RWHP and 4.10 gears, P275/40-17 tires
0-60 mph - 4.17 sec.
0-100 mph - 10.27 sec.
0-60 ft. - 1.91 sec.
0-1/8 mile - 8.17 sec. @ 90.80 mph
0-1/4 mile - 12.59 sec. @ 114.15 mph
0-150 mph - 24.29 sec.
Top speed - 185.06 mph
40-70 mph - 3.29 sec. (3rd gear start)
60-150 mph - 19.65 sec. (3rd gear start)
100-150 mph - 14.02 sec. (4th gear start)

RX-7 w/~320 RWHP and 4.33 gears, P275/40-17 tires
0-60 mph - 4.12 sec.
0-100 mph - 10.24 sec.
0-60 ft. - 1.85 sec.
0-1/8 mile - 8.17 sec. @ 90.94 mph
0-1/4 mile - 12.61 sec. @ 114.91 mph
0-150 mph - 23.90 sec.
Top speed - 181.40 mph
40-70 mph - 3.08 sec. (3rd gear start)
60-150 mph - 19.21 sec. (3rd gear start)
100-150 mph - 13.73 sec. (4th gear start)

Basically, a little lower top speed, a little quicker (0.2-0.3 sec.) on the high end, and very little improvement below 100 mph and in the quarter mile.

If you're drag racing, you'd be better off with 4.50s or 4.77s, probably, but 4.33s aren't worth the performance gain, in my opinion. If you're not a drag racer, stick with the 4.10s. They're "free".

Yep. You'll increase reliability, and you didn't waste $450 on 4.33 gears.

the_glass_man

iTrader: (2)

Hey Jim could you do the test for 4.77 gears as well???

jimlab

Sure. I'll run 4.50s, as well.

RX-7 w/~320 RWHP and 4.50 gears, P275/40-17 tires
0-60 mph - 4.10 sec.
0-100 mph - 10.18 sec.
0-60 ft. - 1.82 sec.
0-1/8 mile - 8.17 sec. @ 89.05 mph
0-1/4 mile - 12.61 sec. @ 115.35 mph
0-150 mph - 23.59 sec.
Top speed - 178.39 mph
40-70 mph - 2.95 sec. (3rd gear start)
60-150 mph - 18.89 sec. (3rd gear start)
100-150 mph - 13.48 sec. (4th gear start)

RX-7 w/~320 RWHP and 4.77 gears, P275/40-17 tires
0-60 mph - 4.70 sec.
0-100 mph - 10.05 sec.
0-60 ft. - 1.79 sec.
0-1/8 mile - 8.19 sec. @ 86.78 mph
0-1/4 mile - 12.61 sec. @ 115.49 mph
0-150 mph - 23.25 sec.
Top speed - 173.32 mph
40-70 mph - 2.76 sec. (3rd gear start)
60-150 mph - 18.57 sec. (3rd gear start)
100-150 mph - 13.26 sec. (4th gear start)

First thing you'll notice is that the 0-60 mph for the 4.77 gears jumped back up towards 5 seconds... that's because there would then be two shifts before 60 mph, instead of one. Car Test recommended shifting from 2nd to 3rd at 7,450 rpm at 59 mph. Holding 2nd gear a little longer would result in a lower 0-60 mph time, if that were all you were worried about, but note that 0-100 is down to almost 10 seconds flat with the 4.77s.

Second thing you'll notice is that the car gets noticeably quicker without any increase in horsepower in the higher speed range. 4.77 gears would gain you over a second (1.10 sec.) from 60-150 mph over 4.10 gears without any other changes. From 100-150 mph, you'd gain almost 0.8 seconds. Not bad for no increase in horsepower, and on a track with higher speed corners and straights the car would be substantially quicker overall.

And third, you'll notice that quarter mile performance doesn't really change. And won't, on street tires. The advantage of the shorter gears is lost on street tires, and would only increase the chances of tire spin on the launch. The Car Test recommended launch points for each gear set for maximum acceleration and minimal tire spin are:

4.10 - 1,600 rpm
4.33 - 1,300 rpm
4.50 - 1,200 rpm
4.77 - 1,200 rpm

If the car were on slicks, then you could take advantage of the gearing. Simulating 26x10.50" slicks on the same car, you'd get the following...

4.10 - 12.09 sec. @ 115.31 mph, 6,100 rpm launch
4.33 - 12.07 sec. @ 116.15 mph, 6,200 rpm launch
4.50 - 12.04 sec. @ 116.70 mph, 6,100 rpm launch
4.77 - 12.03 sec. @ 116.67 mph, 6,300 rpm launch

The results would be more noticeable with more horsepower, obviously, but you'd probably pick up a tenth or so and about 2 mph in the traps, just from the gearing change, all other things staying the same.

So how does a gearing change affect normal cruising rpm and highway mileage? With P275/40-17 tires...

Cruising - 30 mph, 3rd gear
4.10 - ~2,241 rpm
4.33 - ~2,367 rpm
4.50 - ~2,460 rpm
4.77 - ~2,607 rpm

Cruising - 70 mph, 5th gear
4.10 - ~2,700 rpm
4.33 - ~2,855 rpm
4.50 - ~2,967 rpm
4.77 - ~3,145 rpm

Mileage (estimated)
4.10 - 16.7 city, 26.2 highway, 19.9 combined
4.33 - 15.9 city, 24.9 highway, 19.0 combined
4.50 - 15.3 city, 24.1 highway, 18.3 combined
4.77 - 14.5 city, 22.8 highway, 17.4 combined

SanJoRX7

The rx7store has the KAAZ LSD for $800, which probably means you wouldn't have to pay $200 for shipping/duty, etc.

Seems like it might be worth it if you don't care about the 4.33 conversion (note that I didn't say "upgrade" )

patrick

jimlab

Well, a clutch-type limited slip differential will (by definition) allow some slipping of the clutches (which will eventually wear out and need replacement) and would "absorb" some small amount of drivetrain shock, but I wouldn't rely on the differential to absorb any significiant amount of stress that it will not pass on to the axles. Kaaz owners can still break axles easily on slicks with enough power. All you've really done is just upgraded one weak point and high-lighted the next.

The Kaaz is designed for road course work, but of course works just fine in a drag racing capacity also. If we could convince Powertrax to build a no-slip locker for the RX-7's 8.0" (203mm) 10-bolt ring gear, we'd be in business. More on that in a bit...

Here's some interesting information on Limited Slip Differentials (LSD).

LSD's come in a variety of designs. Most use friction plates, cones and/or gears to reduce slippage between each of the tires. these units have a dual power path from the differential case to the axle shafts. Some power is transmitted through the spider gears to the side gears in the conventional manner. The remainder is transmitted by friction between the differential case and the clutch plates and the side gears.

A certain amount of "clutch preload" is built into the unit in a static condition. Then, as load is applied to the differential, the separation forces between the spider gears and the side gears increases this clutch loading. This increase in friction provides for a good positive power flow from the case directly to the side gears.

When traction is available to both wheels, the power going to the differential causes the plates to bind tightly together, giving even power to both wheels. However, in a situation where there is little or no traction available to either one wheel or the other, the amount of power that can be transmitted to the other wheel which has traction is dependent on the friction or "preload" in the clutch plates.

High levels of "clutch preload" will result in good torque transfer but some chattering of the clutches during cornering may occur. (As with the Kaaz...) Lower levels of preload results in minimal chatter but reduced levels of torque transfer to the wheel with traction.

Because LSD's restrict true differential action, tire wear is accelerated. Changes in vehicle handling may also occur, particularly in short wheelbase vehicles. Wear rates on limited slip differentials are generally higher than on other types due to the reliance on friction to reduce wheel slippage. Also, special lubricants may be required to minimize rough and noisy operation.

Despite their limitations, LSD's are popular as original equipment options as well as an aftermarket replace because:

1) Some traction improvement off road is provided
2) Vehicle handling idiosyncrasies are not excessive
3) Installation is simple
4) Cost is reasonable

And now the Powertrax locking differential (and locking differentials in general)...

Unlike limited-slip/posi differentials, locking differentials deliver 100% of engine torque to both wheels, even if one has zero traction. The wheels are mechanically "locked" together when the vehicle is traveling straight ahead. As the vehicle begins to turn, the differential automatically unlocks to allow required wheel differentiation throughout the turn, and then automatically re-locks. Although not as smooth and as quiet as limited-slip/posi differentials, vehicles equipped with automatic locking differentials provide differentiation and the highest level of traction output.

Basically, you'd be trading the clutch chattering during cornering for a "pop-click-click-click" noise, but you'd have superior power transfer in a straight line for drag racing. Everything costs something.

With enough power on slicks or drag radials, you'll probably be capable of breaking the axles regardless of which differential you use. Your differential will just be stronger and better able to handle the abuse if you upgrade to the Kaaz, Cusco, Amemiya, or other units. The stock Torsen differential will work very well in road course/open road activity, but was never made to handle burnouts or drag race launches, especially not with any sort of wheel hop.

I talked to Ari Yallon at length about his efforts to increase the reliability of the back of the car. His comments were that once the Kaaz differential was added, you'd eliminated one weak point in the system, but that the stock axles were still too weak to take a high horsepower/high rpm launch on slicks or drag radials. They are design to break in a specific spot (and do) and the 300M Chromemoly replacement axles that were developed eliminate this "weak point" designed into the axle, so now breakage can occur anywhere along the axle. Very few people are making enough power to break the 300M axles. However once Ari had to move to a street tire and didn't have a true slick to absorb some of the shock of the launch, he started breaking the 300M axles, also. Then he switched to 350M axles, and although he wasn't breaking axles any longer, now the inner axle shafts (which inserts into the differential carrier) were being twisted and sheared off, and the dog joint housings (green "cup" into which the axles insert) were cracking. He cryogenically treated these components and although they check them for shifting and damage after every couple of runs, he said he had not broken a set yet, although this was several months ago when we had this conversation.

The next weak point is the cast iron differential carrier itself. Eventually, the ring gear is going to want to "walk" out the front of the carrier because of the load on it, and the nose of the carrier housing will eventually fatigue, crack and seperate. Ari said that they'd done some strengthening of the carrier housing by welding reinforcements to it, but it's an imperfect solution.

Mind you, this is for 500+ RWHP drag racers. Most people aren't going to see these levels of abuse, and so a Kaaz differential is all they really need for the street to absorb the usual abuse of wheel hop and so on. In other words, unless you're drag racing on slicks or drag radials and making 400+ RWHP, you probably don't have to worry about your axles.

justin

I went to 4.33s and did not see any real change in the et.Trap speed increased about 2mph to 115-116.
In hindsight the kaaz unit would have been a better mod as I wouldn't constantly be thinking that the next holeshot could be it...
I've been lucky so far w/drag radials the rear diff and axles have over 25-30 launches w/o ill effects.
I do however run a full launch kit to try and eliminate the wheel hop.
The 4.33s with stock wheels and tire size put your speedometer @5 mph faster.

GoRacer

iTrader: (2)

...or maybe I should be happy?

I was thinking of getting the 4.30 from Mazdacomp (stock on the RZ), since I have to have my transmission worked on anyhow (synchros).

Fritz Flynn

iTrader: (263)

If you guys decide to buy a used diff. I have one in very good condition and recently inspected and resealed by high tech automotive in Manasas Va. I will let it go for 450 shipped. 60k miles never any drag work but was used some on road courses.
Thanks,
Fritz

3rdGen7

Cool .. I´ll let you know but I think I am set to go with the KAAZ and the 4.33

3rdGen7

I seem to have deleted the pm you sent me by mistake. Please re-send. Also, I found someone who sells the Cusco LSD for $800 shipped and I know someone with a used OE LSD for sale if anyone is interested.

the_glass_man

iTrader: (2)

Where can you find the 4.5 gears?