Rule Interpretation for STX

[lmichael]

I've had a number of people recently state a specific rule incorrectly (in my belief anyway), so I thought I'd throw it out to our collective group. I'm looking for clarification on paragraph 14.11.A.5.

This paragraph states:

"Only standard (as defined in Section 12.4) limited slip differentials (LSD) are allowed on AWD vehicles. For AWD vehicles that did not come with any type of limited slip differential )including center differential or transfer case), a single after-market LSD may be added. 2WD vehicles may use any LSD unit."

In my case, I have a "2WD" vehicle. So, referring to the last sentence, my interpretation would allow any manufacturer (Quaffe, etc.), any style (variable or constant), and any ratio (non-stock) of limited slip.

Is my interpetation correct? If not, why not?

Thanks in advance for your collective wisdom.

[00 SS]

I believe your interpretation is correct. That same rule carries over to STU and when I looked into running that class with my Camaro, my aftermarket diff was legal. Many of the Mustang STX cars use an aftermarket diff as well. "...any LSD unit" means anything that will fit into the stock housing, aftermarket or not.

[Donnie]

YES that is correct

[russjnco]

That's the way I've interpreted that rule as well, unfortunately that stipulation means I can't replace the front viscous diff with an LSD to match the one I already have in the rear......

[Van]

That is the way I was reading it too. And I'm glad I was reading it right.

LSD is one of the last things that will be done to our car just in case we decide to run STS instead of STX.

[Captain_Solo]

Yup. AWD-stock equipped, factory LSD's only. RWD/FWD-any LSD you want that will fit.

[lmichael]

Thanks for everyone's verification of my interpretation.

Unfortunately, that means another $1500 to $2000 will need to be spent :D

And, there may be a stock ratio BMW LSD for sale soon... ;)

[mannix]

"In my case, I have a "2WD" vehicle. So, referring to the last sentence, my interpretation would allow any manufacturer (Quaffe, etc.), any style (variable or constant), and any ratio (non-stock) of limited slip."

--

I agree with one exception - the RATIO is independent of the limited slip. The rule you cited does not allow gear ratio changes; it allows you to use any limited slip - gear type (Quaife/Torsen), clutch pack or welded.

The ratio changes are not included in that; the rule refers to the differential itself, not the ring and pinion.

I'm not fully up to speed on the STX ruleset, but I suspect it is similar to the SP ruleset with regard to gear ratios.

Transaxles must be updated/backdated as a unit (FWD cars, or the RWD cars with transaxles - Porsches (some), MR2/spyder, etc. SO, you cannot change the gear ratio in your transaxle car - you have to choose the transaxle which has the best gearset for your application - ring & pinion + gears.

In a RWD car, with a separate differential, BMW, Camaro, etc etc etc, you can update/backdate from any car on the same line (remember, SP rules here, not necessarily STX). I believe the automatic E36s have lower gears (higher numerically) than the manuals - that'd be fair game in SP.

You cannot put in a different ring and pinion, beyond the U/B allowance - let's say that the E36 M3 was the only E36 to get the 5.88:1 gearset. OK, fine - if you have a BSP E36 M3, go right ahead.

DSP E36 325i? Nope - you have to use a gearset available in a car on the same line.

Make sense?

Not 100% sure if I interpreted your message correctly, but I *think* that's what you're getting at - you're going to change the gears *and* LSD. The gears are OK, as long as another car -on the same line- in the rulebook was available in the US.

Again, that's the SP way. I do believe the STX rules are similar, if not the same, but check before spending;).




Iain (check twice, spend once)

[Captain_Solo]

I totally missed that, but you're right Ian. The Diff can be upgraded, but the Final drive can't be changed. Lee, don't worry I won't tell anyone, unless you beat me!;)

[lmichael]

Well Iain, that was my underlying motive... ;) I guess I'm going to need to get further clarification on the use of the word "any" in that sentence.

As for upgrading, that doesn't apply in my case since my particular model (1993 325is) came with the specific LSD that is currently in the car. The automatic in the same year had a shorter final drive ratio, but without running an automatic transmission, and based on your expanation, I couldn't change to that ratio either.

Maybe it's time to ask the question of the SEB and/or STAC... :confused:

[Captain_Solo]

Actually, if you look in the rule book, it's pretty clear. The LSD is considered a seperate component from the final drive gear. LSD's are mentioned, updating/backdating final-drives is not. If it's not specifically allowed in the rule book, it's illegal. Sorry Lee.

[lmichael]

Actually, if you look in the rule book, it's pretty clear. The LSD is considered a seperate component from the final drive gear. LSD's are mentioned, updating/backdating final-drives is not. If it's not specifically allowed in the rule book, it's illegal. Sorry Lee.

Actually Dylan, I have read the rulebook, the preceding sections, the exceptions, and all the cross references, etc. (that's the kind of thing I do for a living, interpreting legal and other legislative language and trying to figure out what is really meant...). And I don't think it's "pretty clear" at all.

If that's the real intent, I may end up suggesting some language which clarifies the rule. All I've found is opinions (here and in sccaforums), not based in specific language in the rules. The closest thing I've found is paragraph is 13.10.L (in the Stock Category) which identifies that LSDs and differential ratios must be standard. And, maybe that's where the opinions originate... Again, clarification language would be nice, not just "tribal knowledge" and opinions.

On the bright side, I can spend the $2K on an exhaust system instead!!!

[Captain_Solo]

Some clarifying language would be nice. Either way, it looks like your car will end up faster. We'll all have to watch out :)

[00 SS]

I agree that the final drive ratio may not be changed under this allowance. As an example, in SP classes, the differential type is open to anything from open to a spool but the final drive ratio must be stock and can only be changed under the update/backdate provisions. Therefore, the only final drive ratio's than can be used are the ones available on another year of version of your vehicle. I know this does not apply to ST unless they have similar update/backdate allowances.

Originally I thought the ratio you were refering to was the bias ratio of the gear type LSD, that may be changed under this allowance.

This general understanding of these provisions has been the concensus for long time. Please ask the SEB for a ruling, but I'd be suprised if they don't consider the final gearing ratio and the LSD to completely separate issues.

[mannix]

You can _absolutely_ use the automagic transmission ring and pinion in your differential housing, with any LSD that meets the differential rules (AGAIN, I'm Street Impaired guy, but I believe the rulesets are the same in these two cases).

A transaxle is a transmission that includes the differential. FWD cars have them, 911s have them, E36 BMWs do not.

SO - you can (in SP, I'll read the stx rules tonight or tomorrow) update/backdate the automatic ring and pinion perfectly legally. You can bolt it onto a Torsen type differential. It does not matter what transmission the car has; the SP update/backdate allowance reads:

"Engines, transmissions and transaxles must be updated/backdated as a unit."

From that - you cannot put the head from a 92 onto a 95 block (generically speaking).

You cannot take the second gear from an IS transmission and use it in an I transmission (generic, again, for example).

You cannot put a different ring and pinion into your rabbit transaxle.

You CAN swap tranny A for tranny B, as long as tranny B was available in a car on the same line.

You CAN swap an 84 Rabbit GTI motor into a 77 Rabbit, provided you take the whole MOTOR - oilpan to valve cover.

Getit?

In a nutshell, if the STX rules for differentials are the same as SP, you can use any final drive (ring and pinion), as long as a car on the same line came with said final drive.

You, per the limited slip allowance, in a 2wd car, use any type of limited slip.

The ring gear bolts to the limited slip. That's it. There are allowances pertaining to both of them - the update/backdate allowance does not specifically mention "ring gears" - it simply tells you what you must use "as a unit."

Engines.
Transmissions.
Transaxles.

Your rear differential != the above. So, fair game - grab the final drive out of an automatic, get Kevin Wenzel to ramp the stock IS limited slip, buy some new discs/thick shims, get some 80w90NS gear oil, voila, no more wheelspin, better (I'd hope;) gearing.

Legally, even.



Iain (if it is a DSP car.....;)

[mannix]

I just took a quick look at the 2005 Street Touring ruleset. I see nothing allowing update/backdate in ST.

So, you're right - you *would* have to have an autotranny to use the automatic gear ratios.

Surely someone here knows more about ST* - Roger? Am I missing an update/backdate allowance? Huh. I guess if it is to fit between stock and SP, eliminating u/b makes sense, but that really places more of a premium on the Right Car.

Come to the dark side. Street Prepared is your friend;).




Iain

[kwenzel]

I just took a quick look at the 2005 Street Touring ruleset. I see nothing allowing update/backdate in ST.


I think they chucked that allowance after people started complaining about the hybrid Hondas that were at the top of the field - nobody had really exploited U/B up to that point, and the rule didn't help the previously-popular RS2.5 Subarus at all. It *was* there in the beginning, though.

[lmichael]

I just took a quick look at the 2005 Street Touring ruleset. I see nothing allowing update/backdate in ST.

So, you're right - you *would* have to have an autotranny to use the automatic gear ratios.

Surely someone here knows more about ST* - Roger? Am I missing an update/backdate allowance? Huh. I guess if it is to fit between stock and SP, eliminating u/b makes sense, but that really places more of a premium on the Right Car.

Come to the dark side. Street Prepared is your friend;).

Iain

Iain,

I appreciate your explanation on the diffs, and you are correct that there are no update/backdate allowances in ST*. And, I also agree that the "right car" is much more important. Not sure my checkbook is ready to step up to SP...

[00 SS]

Ian,

It looks your interpretation is the same as mine, you need the update/backdate provisions to change the final drive ratio in this type of drive axle because the LSD provision does not cover the gearing.