72 replies to this topic

[Tom Hampton]

We are allowed to use procedures outlined in the Mazda fsm. If Cusco has a factory procedure for adjusting it, then how is it any different?

[Jason J Ball]

My opinion:

1.  If you can find a MazdaComp LSD installed and all ready-to-go for, say, $900-1100, you can look inside it and all seems OK, and you measure breakaway torque and it feels OK, then go that route.  I've never seen one "worn out".

 

2.  If you can't find a MazdaComp or you want a "better" LSD diff, or are trying to make a 1.6 fly, and you have $1600+ to pay for the diff and install parts and labor, go with the Cusco, but have it properly set up and installed.

 

3.  If you just never want any reliability problems (rental car, enduro car, or a diff you plan to take with you for an NB) then put in the '99+ Torsen.

 

I've run VIR, but not in an SM, so I don't know how hard you guys rock the curbs.  Do you get wheelspin with the VLSD after a few laps?

 

Have you run VIR since the new pavement was installed? Oak Tree is the most important turn, but I've only noticed wheel spin there occasionally. And its usually because I've missed my marks. Mind you, I'm running mid 2.23's although my data from October shows I could get into the 21's easily, but I always seem to get skunked by a slower car coming through the uphill esses or south bend. My car seems to fly from 3 to Oak Tree. Its the only thing I don't love running with NASA is the mixed classes. Some of these guys have unintentionally really wide cars. 

[OctaneNation]

The current rule is:
9.1.7.c.2.b. 1990 to 1993 Miatas may use the stock, unmodified viscous limited slip differential or the MAZDASPEED Motorsports Development limited slip differential, part number #QN1064-A00 (previously TOY1-27-200 & 0000-02- 5501). Alternate MAZDASPEED #0000-02-5500 limited slip differential is permitted.

That "alternate" #0000-02-5500 is the cusco unit.

So there no tech shed issue here.

Does 'unmodified' refer to the just the VLSD or both the VLSD and Motorsports diff? No where does it state you can or cannot change the break away torque or ramp angles of the Motorsports LSD. Just saying...

[RazerX]

From a track perspective is there a material difference between the type 1 and type 2 torsens?  I thought the break away torque was pretty similar.   

[Ron Alan]

Stop confusing the issue! Not the same animal with respect to function! But i'm sure the non-serviceable clutch discs come the same in the 1 and 2. I dont think there is a breakaway torque like the clutch packs?

 

With respect to this discussion and adjusting a Cusco...my guess is the unit that is speced in its factory form can not be altered. If it doesnt say you can, you cant.

 

But Tom's perspective is interesting.

[LarryKing]

 

my guess is the unit that is speced in its factory form can not be altered. If it doesnt say you can, you cant.

 

If you watch Saul's first video it can definitely be adjusted.

 

Will it ever be tech'd? (a 1.6 at an invasive tech event, i.e. Majors?) What are the odds? Would the ccc even know what to look for?

 

Ta da - tech shed legal.

[SaulSpeedwell]

My personal position on all things "compliance":  Each customer needs to be aware of, and comfortable with, how his/her vehicle is equipped, and make his/her own determinations on compliance.

 

Cusco publishes a graph on how the breakaway torque changes over time - in the case of the as-spec'd MZ diff, they describe it as wearing rapidly.  The graph does not show any numbers.  I'll try to post a link to it later.

 

From a PRACTICAL standpoint, what that means TO ME, is that nobody would ever be able to protest or scrutineer based on breakaway torque, because:

A.  There is no "spec".

B.  A low-end "spec" cannot be reverse-engineered (as I believe "we" and SCCA did with Bilstein's shocks), because the part is constantly "wearing" in the favorable direction.

 

I have never analysed the GCR in terms of "adjusting" things that are, by design, obviously and intentionally "adjustable".  I'm glad we have never argued about whether tire pressures, ride heights, and cornerweights can be outside what Mazda's books specify.  (Spec E30 didn't have it so lucky!)

 

On the other hand, it would probably be best to clarify this issue much in the way AFM "adjustment", timing "adjustment", and swaybar disconnection were clarified in SM.

 

Parting thought:  Let's imagine we are SRF and this diff was sealed by SCCA. What would we all do?  We would "wear it out" on purpose until it hit the breakaway torque numbers we wanted.  We'd have fixtures to do that and we'd resell "blueprinted" sealed LSDs for 3X the cost (or just not tell anyone the "speed secret").

 

 

-Mark

[Rob Burgoon]

 

 

Will it ever be tech'd? (a 1.6 at an invasive tech event, i.e. Majors?) What are the odds? Would the ccc even know what to look for?

 

 

Will a 1.6 ever need to be teched? 

 

Ba dum tsssh!

[Steve Scheifler]

Definiteky OK to adjust, no different than your mirrors and many other things designed for adjustment. Not even a meaningful argument against IMO. At worst you could argue that switching "ways" crosses the line into modification rather than adjusting, but I'd argue the other and that it should be spelled out explicitly if not allowed to go 2-way or whatever.

[Rob Burgoon]

So why do we want locking on decel again?  Is it one of those "force my tight car loose on decel so my turbo can put more power down on exit" kinda things?

 

Wouldn't a miata want 1 way due to lack of power oversteer issues?

[Steve Scheifler]

More about stability under braking, I think. Might be especially good when trail-braking from high speed through a slight bend.

[RazerX]

 

 

As for the Torsen:  In A-B-A testing with a fast driver at Torsen-unfriendly (wheelspin-inducing) track, the Comp LSD is faster.  This was a blueprinted low-breakaway torque Comp LSD versus a "stock" Torsen.  The Miata NB Type II Torsen CAN be improved with blueprinting, but miracles cannot be performed.  It only has an itty-bitty baby "clutch" in it.

 

 

 

 

Stop confusing the issue! Not the same animal with respect to function! But i'm sure the non-serviceable clutch discs come the same in the 1 and 2. I dont think there is a breakaway torque like the clutch packs?

 

With respect to this discussion and adjusting a Cusco...my guess is the unit that is speced in its factory form can not be altered. If it doesnt say you can, you cant.

 

But Tom's perspective is interesting.

 

Ron, i was not confusing the issue, i was in fact responding to the opening post by Mark.  I know you are interested in the legality of the adjust-ability.  And I was similarly curious how different the breakaway tendencies are between the type 1 and type 2 given they are different.  Are both adjustable?

[SaulSpeedwell]

So why do we want locking on decel again?  Is it one of those "force my tight car loose on decel so my turbo can put more power down on exit" kinda things?

 

Wouldn't a miata want 1 way due to lack of power oversteer issues?

 

I don't think you are crazy - the 2-way clutchpack LSD is one of the oldest/simplest designs, which seems best suited for "drifting" these days.  On the other hand, BMW used 2-way LSDs a lot - but since they can't make a cooling system or front lower control arm that will last more than 70K miles, I'm not sure they are as infallible as some would have you believe.

 

If you ARE happy with how a car handles with a 2-way, then getting rid of the decel-side "locking" CAN throw you off.  In a traction limited car, it can make the car loose under trailbraking and turn-in, with a transition to understeer when on the gas, killing some momentum along the way.

 

But, my theory is SM drivers are aces that will the car to 10/10ths despite its various theoretical weaknesses, and THAT guy will want and need as much "efficiency" from his LSD as possible - meaning he wants the "locking" minimized to one eyelash above the point of wheelspin.

[Rob Burgoon]

I don't think you are crazy - the 2-way clutchpack LSD is one of the oldest/simplest designs, which seems best suited for "drifting" these days.  On the other hand, BMW used 2-way LSDs a lot - but since they can't make a cooling system or front lower control arm that will last more than 70K miles, I'm not sure they are as infallible as some would have you believe.

 

If you ARE happy with how a car handles with a 2-way, then getting rid of the decel-side "locking" CAN throw you off.  In a traction limited car, it can make the car loose under trailbraking and turn-in, with a transition to understeer when on the gas, killing some momentum along the way.

 

But, my theory is SM drivers are aces that will the car to 10/10ths despite its various theoretical weaknesses, and THAT guy will want and need as much "efficiency" from his LSD as possible - meaning he wants the "locking" minimized to one eyelash above the point of wheelspin.

 

Since I posted that I chewed on it some more and am thinking locking on decel would be similar to shifting the rear braking to brake a little less on the inside rear and serve to stabilize the rear some.  This could allow for an aggressive rear bias for braking straight, while pissing off the car less while trail braking.

 

So right now my chewed pencil is telling me I'd want 2 way unless it made my car act stupid (i.e. push or snap loose) while trail braking.  With luck, we won't see much of this silly behavior since we would be tuning our clutch packs to "one eyelash above wheelspin" with near zero preload.  OTOH, braking hard will press the clutches together harder than pressing the gas ever would, so need to test.

 

Fun to think about.

 

Do torsens do much of anything on decel?

[OctaneNation]

How much Cusco breakaway tuning can be done just with fluids?

[SaulSpeedwell]

Since I posted that I chewed on it some more and am thinking locking on decel would be similar to shifting the rear braking to brake a little less on the inside rear and serve to stabilize the rear some.  This could allow for an aggressive rear bias for braking straight, while pissing off the car less while trail braking.

 

So right now my chewed pencil is telling me I'd want 2 way unless it made my car act stupid (i.e. push or snap loose) while trail braking.  With luck, we won't see much of this silly behavior since we would be tuning our clutch packs to "one eyelash above wheelspin" with near zero preload.  OTOH, braking hard will press the clutches together harder than pressing the gas ever would, so need to test.

 

Fun to think about.

 

Do torsens do much of anything on decel?

 

I think most of the on-paper and in-theory thought experiments - and much of what Carroll Smith wrote - goes out the window in SM.  When you have underpowered, overtired, oversprung, underdamped, almost-no-shock-travel production cars being hurled around by truly great drivers at 10/10ths, in a class where 0.3 seconds will take you from pole to 4th row .... you really have to rely on A-B-A testing.

 

My thinking is the great drivers and car prep wizards will figure a way to get the car around the track regardless of the "way" of the differential.  But give those guys an extra couple ft-lbs (or fix their wheelspin), and their laptimes WILL drop.  That's why I'm focused on making the diffs "faster" in terms of minimizing the "locking" when you don't need it.  Or, in the case of the T-2 Torsen, trying to make it more sensitive and have higher Torque Bias Ratio.

 

The Torsen under coast - the Wiki answer is it goes "open".  The real answer is that all the Torsen "knows" is the torques and position of its 3 "ports".  From a practical standpoint as a driver, it feels like a 1-way LSD that annoyingy becomes an "open" diff when you curbhop or lift/lighten a drivewheel for any other reason.  It is a great street diff, and a great AWD center diff, but it isn't an ideal competition diff.

[SaulSpeedwell]

How much Cusco breakaway tuning can be done just with fluids?

 

Zero to 5 ft-lbs, in my experience.  The same for the MazdaComp.  But it is worth considering, because when we set an LSD an eyelash above wheelspin, your easiest "tuning" method then becomes fluids. 

 

The problem I've seen is once you are too low (too much LSD additive), it is hard to get back.  You have to wash, sometimes even WIPE, the LSD additive off the clutch packs.  In both the Torsens and the Comp/Cusco, the ShockProof products seems to turn into a congealed "grease" around the "clutches".

[OctaneNation]

Interesting. I would have thoughts that fluid would have made a bigger difference.

 

How would you recommended setting up a and breaking in a new 2 way Cusco MZ? Is it possible to disable clutches as described here: http://www.motoiq.co...sco-RS-LSD.aspx

 

Just a wild guess, and I'm sure it's track dependent, but breakaway could be say reduced by 60% and then keep tuning down with LSD additive? What fluid would be best to start with? One with or without friction modifiers?

 

Your insight has been super helpful already.

[SaulSpeedwell]

Interesting. I would have thoughts that fluid would have made a bigger difference.

 

How would you recommended setting up a and breaking in a new 2 way Cusco MZ? Is it possible to disable clutches as described here: http://www.motoiq.co...sco-RS-LSD.aspx

 

Just a wild guess, and I'm sure it's track dependent, but breakaway could be say reduced by 60% and then keep tuning down with LSD additive? What fluid would be best to start with? One with or without friction modifiers?

 

Your insight has been super helpful already.

 

Since you'll be $1200-1600 into it anyway, your best bet is sending the diff to someone who has some experience and tools in trying to fit your diff to the car.  If you like DIY-ing more than reducing laptimes (not being crass here, many SCCA folks fit in this category), then start with a non-LSD additive fluid, take out clutch discs per the Cusco manual until you are below 10 ft-lbs on the bench, then test it, then add LSD additive if you have no wheelspin. 

 

The problem with the MZ is it "wears" fast, so today's Goldilocks setup may be next years Spin-O-Matic ....

 

(P.S.  The MotoIQ link is not directly applicable to the MZ diff, since the MZ diff does not have "springs" like the RS ... email me if you are serious about attempting to "blueprint" an MZ)

[OctaneNation]

FYI Mazdacomp says 2-3 months to get a Cusco as they are out of stock and sea transport is taking longer than usual due to strikes...