26 replies to this topic

[forestdweller37]

Hello!
I picked up a 1994 Spec Miata that was last raced in 2005 and I'm working on getting it brought up to date per the latest safety and competition rules. At this point, all I want to do is get on the track with a legal car and have some fun with my local SCCA region. The safety side is done, but some of the SCCA rules have me a little confused regarding the rear ring and pinion.

Rule 9.1.8.3.a says the final drive ratio must remain stock to the year of the car. That's 4.10 to 1 for a '94. And the rule 9.1.8.3.c says the car can use a Torsen diff, but that the stock gear ratios must be used. Twice now it's 4.10 to 1. Got it. Then I get to the lines that specify the wheel base, weight, etc. and there's a note saying that I have to update to the 99-05 4.30 ring and pinion.

What is the intent? Was the rule different back in the 03-05 era?

Just for kicks, I looked into Nasa's SM rules. It looks like they're allowing the 4.10 at any event except their championship. Correct?

Thank you in advance.
-Chris

[Ron Alan]

4.3 for SCCA. NASA can stay 4.1 except the big show! The SCCA rule changed last year...kind of a pain all the way around(cost and performance). I get the intent but it put the 94-97 at a slight disadvantage in my opinion because the rev limiter is at least 200 rpm lower than the 1.6 and 100rpm below the 99+ cars. Some tracks you end up with a shift or come to a speed stop while the other year cars can gain MPH advantage without shifting

[Mike Collins]

Ron is correct. If you have the 4.1 torsen converting to the 4.3 should be cheap. Just buy a 4.3 open R&P

[Jim Drago]

CRB Letter Tracking Number #7361
I sent in a letter to fix this.


Hi Jim,
Thank you for submitting a request/input to the Club Racing Board. The details of your request can be found below.

Letter ID Number: #7361
Title: Correct rule on final drive ratio
Class: SM
Request: Rule 9.1.8.3.a says the final drive ratio must remain stock to the year of the car. That's 4.10 to 1 for a '94. And the rule 9.1.8.3.c says the car can use a Torsen diff, but that the stock gear ratios must be used.

This from a post on Mazdaracers.com, we should correct it.


Thanks

Jim

[Bench Racer]

Twice now it's 4.10 to 1. Got it. Then I get to the lines that specify the wheel base, weight, etc. and there's a note saying that I have to update to the 99-05 4.30 ring and pinion.

Thank you in advance.
-Chris

Chris, this is a note for clarification/understanding the rules as written in the GCR/SMCS. The Spec Line which is the last page of the SMCS overides the previous SMCS pages. IIRC a Fastrack announcement will override all previous rules.

[forestdweller37]

Thanks everyone. And thanks for writing a letter to get the rules clarified for the next newbie.

I'll keep my eyes open for an inexpensive 4.30 open diff. Every 4.30 I've seen out there so far has been priced well above Mazdaspeed's price for a new final drive gear set. Hopefully something will present itself before the season starts.

-Chris

[Greg Kimble]

Chris,

Locate a used 4.3 open diff, take that diff and your 4.10 torsen to your favorite SM shop and they can swap the torsen into the open 4.3 pretty quickly ( the shop we deal with did it while we waited). So for the cost of the open diff and $75 in labor we were good to go.

Greg

[Tom Sager]

Anybody know what the weight difference is between a 4.1 R&P and a 4.3R&P ?

[Ron Alan]

Anybody know what the weight difference is between a 4.1 R&P and a 4.3R&P ?

.2??

[Doug007]

That's some nice low CG weight. 4.3 will have more teeth but nothing that shouldn't be able to taken care of with a slight change in fueling or ballast.

[Tom Sager]

.2??

My guess is that it's more than that. I'm sure somebody has put those parts on a scale.

[Jim Drago]

My guess is that it's more than that. I'm sure somebody has put those parts on a scale.

My guess would be similar or less than .2
I have not weighed though.
Diameter is the same.. two extra teeth on the 4.3 over the same circumference and same amount of teeth on the pinion.

[Tom Sager]

My guess would be similar or less than .2
I have not weighed though.
Diameter is the same.. two extra teeth on the 4.3 over the same circumference and same amount of teeth on the pinion.

Assuming you're right then it's not enough to matter.

[Jim Drago]

Assuming you're right then it's not enough to matter.

Even if it did, it wouldn't matter as we can only run the one gear

[Ron Alan]

My guess is that it's more than that. I'm sure somebody has put those parts on a scale.

4.3 - 4.1=.2 Sorry you thought I was serious But the difference in speed at 6900rpm between the 2 is at least 2mph in 4th gear...which sucks when the 1.8(NA)had to go to the 4.3 with it's lower rev limiter! Like how I got that on in there Jim! Back to the topic

[Tom Sager]

4.3 - 4.1=.2 Sorry you thought I was serious But the difference in speed at 6900rpm between the 2 is at least 2mph in 4th gear...which sucks when the 1.8(NA)had to go to the 4.3 with it's lower rev limiter! Like how I got that on in there Jim! Back to the topic

Around here we have NASA and Midwestern Council and people might choose to run a 4.10 for either budget or track reasons. The gentleman in Des Moines might want to run those events. I was interested in the weight difference of the gear mostly because somebody else who runs a '94/'97 was bitchin at me more than a year ago that we got hosed with the change to 4.30 due to the extra weight of the ring gear and the rev limiter. I think the change to 4.30 was overall a positive one (but only very slightly). There are a couple tracks nearby (Blackhawk and Autobahn) where I would prefer a 4:10 due to shift points and the rev limiter. At Road America I'd much rather be climbing the hill on the front straight with a 4.30.

[DrDomm]

I'm in the same situation as the original poster. I found a Torsen 4.3 for $800, and "popped" it in. I now have the 4.1 Torsen, and will save it til I find a nice cheap open 4.3.

On to all the other necessary updates/maintenance/bodywork...

[ralt12]

I have searched for any discussion on the proposed rear drive ratio rules change for the 94-97's, and come up short. Seems to me as though with weight (low cost) and restrictor plate changes (low cost) the rules makers could have come up with a better plan than having to change the rear drive ratio that came with the car (NOT low cost).

I'm going to admit being a dunce on this--can anyone point me to the discussion?

[Greg Kimble]

Not sure what kind of discussion you are looking for, but in summary, the 94-97 cars are the only years with a 4.10 ring and pinion, all other years have a 4.30. In order to place the cars on a more equal footing, it was decided to have the 94-97 cars switch to the 4.30. Since all years of transmissions have the same ratios, now all cars have the same gears across all years. The most common solution to switching to the 4.30 is to find an open 4.30 rear end out of a newer car and have your existing torsen switched into the open rear end.

Greg

[James York]

Don't know about any discussion on here. But it's the rules, not optional, and I believe it was partially an effort by the rule makers to get the cars more the same.