ITA miata Differential

There is much talk on the SM board about allowing the '99 torsen differential to be grafted on to the
'90 thru 92 miatas.

As I am having my third mazdaspeed rear end put on my '91 miata (in three years) it seems like the torsen swap would be a great option to help keep the costs down and the car reliable.

Would the rule change end up applying to ITA? If the rule change happens and it does not apply to ITA then
I guess SM cars would not be able to run in ITA with that differential.

Would it make sense to lobby with the scca to include ITA in the rule change?

Thanks for any information about this.

Regards,

Neal Norton

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Would the rule change end up applying to ITA? [/b]

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No. Changes in SM rules to not affect IT rules.

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Would it make sense to lobby with the scca to include ITA in the rule change?[/b]

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Yes, if you want it changed. Email [email protected] with your rule change request. It will be sent to the ITAC for consideration. - GA

I'm not sure that I know what you mean by "grafted on".

I am aware of issues with the Miata diffs, and recently it was brought before us (the ITAC) to allow diff and transmission coolers. (the main reason being the ongoing issues with Miata diffs and the desire for class crossover ease) I thought the allownce would be fine, as it really has no performance increase, at least in terms of lap times, but it didn't make it as the CRB felt there was no real pressing need and wanted us to keep the rule creep under control.

On this, if I understand your intent accurately, I fear the answer will have to be a "no". Here's why:

-IT rules are category-wide. Whats good for the goose is essentially good for all the ganders. So, the allowance of alternate differentials (and I assume this is not a 'in case" swap), would be extended to all cars. Listing it as a line item is really something that is against IT philosophy. It has been done, years ago, in rare instances, and the ITAC is working to close such allowances wherever possible.

Alternate ltd slips are currently allowed in IT, but they must fit within the stock housing. The fwd guys are using all sorts of devices, like the phantom grip, the OMP unit, and so on.

Take a good look at the IT rules regarding this, and perhaps there is a way to make it work in the SM world if they are open to rules allowances for this problem.

Of course you are welcome to write the letter to the CRB/ITAC, but my thinking is that it will be an uphill battle at best...but I could be wrong!

Thank you Greg and Jack for the information.

I am coming from SM and I am just starting to get my feet wet in the IT world.

Regards,

Neal

I believe the later diff requires a larger housing. That would make it illegal in IT. Similar to using a turbo diff in an RX-7.

[Edit]: Along with the larger housing you'd have to allow alternate stub shafts. Not sure about the drive shaft.

Let me see if I can get this correct.

Spherical bearings are a ok because they are cheaper, bla bla.............

The 1.6, 6 inch ring gear rear end which was week at the get go can not have a rule change so that the 1.8 7 inch ring gear rear end may be used. ECONOMICS makes sense for the ring gear just like ECONOMICS made sense for the Spherical bearing.

I would like to tip one :birra: to the rules makers.

David....EVERYBODY....across all car model lines..... had the ability to create a spherical bearing solution for their car. 240SX rear ends HAVE to be set up right, and they were...but it wasn't cheap. In the end, the rule change did not-

-Increase the prep level of any model car in the category over what was already possible, and...
- Did not single out a specific model it gave a "break" to.

A change like this could/will do just that for one car.

Your comparision isn't very valid, IMHO.

***Your comparision isn't very valid, IMHO.***

Please give me a break Jake. I may be getting senior BUT I do remember that you were one of the people who made some razzel dazzle bushings under the bushing material is free & stated it was costly. :( Someone else simply installed Spherical bearings which was very cost effective. :) It would also be long term cost effictive to implement the 1.8 rearend IMHJ.

Topeka or bust ;)
David

marty when replacing the rear end on the 1600 and installing the 1800 rear end you have to replace the axles, stub axles, drive shaft . all its a bolt on deal,, the kit cost about $1000.

I guess I don't follow some of the opposition to this interchange as I do not see this as "rules creep" or creating an unfair advantage. If anything, the larger ring & pinion will add drivetrain loss. The 6" ring and pinion can grenade, and when they do, they usually take the diff with them. That can be expensive. The 7" r&p, its diff, & the housing bolt right up. I believe different stub axels may be required depending on the diff in the original 1.6 housing (open, lsd).

Couldn't this be an "exception" listed in the "Notes" section of the 1.6 Miata's classification line? There seem to be plenty of IT cars with "exceptions" in the "Notes".

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marty when replacing the rear end on the 1600 and installing the 1800 rear end you have to replace the axles, stub axles, drive shaft . all its a bolt on deal,, the kit cost about $1000.
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Exactly. I was just trying to clarify that swapping the diff housing implied swapping other parts as well. A rules exemption for the housing would cascade into quite a few more parts.

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Couldn't this be an "exception" listed in the "Notes" section of the 1.6 Miata's classification line? There seem to be plenty of IT cars with "exceptions" in the "Notes".[/b]

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Will, the vast majority of those notes items are for safety, some are for clarification of installed equipment. Some are for alternate parts because the originals are no longer available (older carburetors, for example). I can find none that are for durability or performance-enhancement allowances. If there are some there where you disagree with me, point them out and we can clarify whey they're there.

If we start allowing rules exceptions for specific models that have durability problems, where does it end? Do we allow Rabbits to modify their knuckles in order to install Audi hubs and bearings, for example? And how do we police these allowances, such that no one cheats? How do we keep someone from CLAIMING they have a durability problem but in truth are looking for a competitive advantage? Doesn't this issue speak directly to the "warts and all" issue of choosing vehicles?

I wholly encourage you to request the changes you want; that's the process. But, if something like this comes up for membership input, I would be one to strongly request that this Pandora's Box not be opened...

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I guess I don't follow some of the opposition to this interchange as I do not see this as "rules creep" or creating an unfair advantage.

So using your logic Will, you'll have no problem with me switching to the 188mm diff case on the 325 instead of the 168mm on the Z3. That'll be great as there a dime a dozen and available in almost any ratio you could want, cheaply. Also, I could by one off the shelf or on ebay with the ramp angle adjustment already done. Still think it'll add driveline loss??? That's exactly what a ramp angle adjustment does....minimize loss.


It's creep.

R

See Gregs post.

Thanks Greg, saved me a lot of typing.

(And yes, the ITAC has gotten a bunch of similar requests for hub swaps, dist gear changes, axle changes and so on, and hte answer is the same, wrong category for that.)

It WOULD be a performance advantage AND a reliability advantage given to ONE make of car, and that's not fair.

Greg, Bob, & Jake,
Thanks for sharing your point of view. I have to admit that I am fairly naive when it comes to "creative interpretation" of the rules, and that I should spend more time considering how a rule could be exploited before posting my opinion on the subject. If there is one thing clear about Bob's post, it is that the rule would be picked apart and exploited to its fullest extent. As a newbie to IT, I guess I'm just not in that frame of mind.

For what it's worth, I suggested that the diff could be allowed in the "notes" section with the following in mind:

• A few IT cars are allowed such things at alternate bearings in the "notes" section
• The 1.6 Miata rearend is a known weak point
• The SCCA has already acknowledged this by allowing the interchange in other class(es)
• A fellow ITA competitor lost his 1.6 r&p and diff during qualifying at the Cheap Date
• The rule proposal is to specifically allow the rearend from the 1.8 Miata, which is also an ITA-classed car
• The chassis of the 1.6 and 1.8 Miatas are otherwise exactly the same: the required OEM part(s) "bolt right up"

No, Will, Doc Bro is just being facetious (reductio ad absurdum).

I hear ya. If it's something you'd really like considered, you need to forward that request to the CRB. Otherwise, it's just us boys arguing on the Internet...

If the ITAC runs out of things to do this fall, they could go through and recommend that all of those "notes" be weeded out of the ITCS. Their presence makes it appear as though that kind of thing IS within the class philosophy.

We all have our list of parts that make up for a "weak point," that we've seen fail (or had fail), come off of similar models, and are bolt-on replacements. I'll join Greg et al. in the "anti box-opening" side of the argument.

K

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If the ITAC runs out of things to do this fall, ......

K
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We seem to keep busy, LOL

It would be cool to go through the notes and exceptions, but I think you'll find them to all be pretty old. I think the ITAC has done a good job in recent years of holding the line on them. You will find some cars that have individual "situations", like ITS cars being dual classed in ITR, but they've gotten there via categorical moves, and they are rarely the only car affected.

this would benefit me directly, but even i can't justify the allowance based on exactly what has been stated above.

PM me for ways to work around this problem on the 1.6 diff.

Agreed. The argument for "low cost" and "reliability" don't work in IT - particularily when some folks are rebuilding their calipers every weekend because they simply won't make it.

If the larger LSD was allowed based on reliability then I know a lot of folks who would like some vented rotors and/or alternative calipers based on reliability - no size increase or performance change (except the brakes will last longer than 20mins), just a different design that will last a weekend.

Doesn't work like that.

Ron