72 replies to this topic

[SaulSpeedwell]

Bench, I guess I forgot the last part of your Q re: "Why Not the MazdaComp?".  The MazdaComp is fine, but getting harder and harder to find in good condition.  I still have parts to rebuild them and tune the breakaway torque, but I think I saw 3 MazdaComp diffs last year that I considered beyond rebuildable (due to case/housing wear/damage). 

 

Without opening up the debate of whether it is legal to adjust something that is inherently, by design, adjustable (a fact specifically mentioned in Mazda's press release re: adding the Cusco to the SM spec line), the Cusco gives us more options - but it is always the competitor's decision how and what we do in that regard, if anything. 

[DavidNJ]

Just checking if I understand correctly: the 1.8L cars all use the Torsen and the 1.6L cars use the Cusco? On that note, isn't a 45° ramp a bit steep for a 100hp car. 

 

From http://www.taylor-ra...ferentials.pdf:

"In general, lower powered cars with lots of tire (Formula Atlantic and 2Liter Sports racers) will use steeper ramps and fewer active clutch/stator interfaces. Additionally, very little preload is used. As a starting point, Formula Atlantic cars will be frequently set up with 80º ramps for both drive and coast, 2 active surfaces per side, and just 10-15 lb-ft of preload."

[SaulSpeedwell]

Just checking if I understand correctly: the 1.8L cars all use the Torsen and the 1.6L cars use the Cusco? On that note, isn't a 45° ramp a bit steep for a 100hp car. 

 

From http://www.taylor-ra...ferentials.pdf:

"In general, lower powered cars with lots of tire (Formula Atlantic and 2Liter Sports racers) will use steeper ramps and fewer active clutch/stator interfaces. Additionally, very little preload is used. As a starting point, Formula Atlantic cars will be frequently set up with 80º ramps for both drive and coast, 2 active surfaces per side, and just 10-15 lb-ft of preload."

The link isn't working, but check the GCR, because I am fairly sure that your statement isn't correct for the NA6, NA8, or NB8.

 

Ramp angle, preload, 1, 1.5, 2 way, and about 20 other things determine how to best get two (or 4) driven wheels down the straight and through the corners the fastest. Our goal is to be fast and reliable.  95% of drivers can't tell the difference in reasonable-but-moderate LSD tuning differences, and 99% of the drivers can't give feedback that will translate into gains.  I'm being serious here, I'm not trying to be a smartass at all.  But when the best drivers pair up with the best preppers, gains can be achieved.  I'm a huge fan of Carroll Smith, but almost everything he wrote will be worthless or misleading as to why any SM Runoffs podium winner beat any P11+ SM Runoffs participant. 

 

In short, an SM ain't an FA.  Not even close.

[DavidNJ]

The link isn't working, but check the GCR, because I am fairly sure that your statement isn't correct for the NA6, NA8, or NB8.

 

Ramp angle, preload, 1, 1.5, 2 way, and about 20 other things determine how to best get two (or 4) driven wheels down the straight and through the corners the fastest. Our goal is to be fast and reliable.  95% of drivers can't tell the difference in reasonable-but-moderate LSD tuning differences, and 99% of the drivers can't give feedback that will translate into gains.  I'm being serious here, I'm not trying to be a smartass at all.  But when the best drivers pair up with the best preppers, gains can be achieved.  I'm a huge fan of Carroll Smith, but almost everything he wrote will be worthless or misleading as to why any SM Runoffs podium winner beat any P11+ SM Runoffs participant. 

 

In short, an SM ain't an FA.  Not even close.

 

b. 1990 to 1993 Miatas may use the stock, unmodified viscous limited slip differential or the MAZDASPEED Motorsports Development limited slip differential, part number #QN10-64-A00 (previously TOY1-27-200 & 0000-02- 5501). Alternate MAZDASPEED #0000-02-5500 limited slip differential is permitted.

 

c. 1994 and newer cars may use the stock limited slip (Torsen or Tochigi Fuji) differentials from 94-05 models. 4.3 gear ratio must be retained.

 

d. The 90-93 Miatas may convert to the 94-05 differential assembly and must retain the 4.3 differential gear ratio. This conversion includes the driveshaft and half-shafts. The original 90-93 model rear suspension uprights must be retained.

Are all the 1994+ differentials Torsen? 

[SaulSpeedwell]

Are all the 1994+ differentials Torsen? 

 

I think this statement is correct:  all of the 1994-2001 1.8 cars are either open or Torsen.  After that, the infamous Tochigi-Fuji comes into play, in various %s of the factory builds.  I don't think I am ruining anyone's secret program or going out on a controversial limb in saying that THAT diff has never done anyone any good, at least not in the NA and NB Miatas. 

I'm not sure what you are trying to figure out here, but it boils down to this:  The "good" 1.6s will be running the no longer available MazdaComp clutch-type, or the recently-legal Cusco clutch-type, OR a 1.8 Torsen swap where durability is more important than the last 0.3-0.5 seconds per lap.  The 1.8 Torsen swap is a good choice for rentals, enduro cars, and people who are more than 1 second off pole and care about durability.  Basic $9K 1.6 cars may also have an open or a viscous LSD in a 1.6L carrier.  The "good" 1.8s will all be running a factory Torsen of some fashion.  Basic $9K 1.8 cars may have an open diff. 

 

I welcome any non-proprietary corrections to the above, as I may be missing some special edition or some VIN break accuracy.

 

I don't know of any good/fast car running the Tochigi-Fuji.  I consider it an expensive recipe for poor performance and poor durability, or what I would normally associate with BMW's LSD (or lack thereof) engineering (or lack thereof) . 

[Killian]

I thought the 2002 still ran the Torsen. Was it a mid-year change?

[DavidNJ]

I guess where I was confused was that the Salisbury tuning was a pointy-end type of thing but I thought there really weren't any pointy-end 1.6 cars at this point. 

[Bench Racer]

Last spring at the Blackhawk Farm Majors race there were 3-4 1.6's turning similar lap times to the 99 plus cars. It takes a consistent pointy end wheelman to perform equal to the 99 plus throughout a race.

[Jim Drago]

Last spring at the Blackhawk Farm Majors race there were 3-4 1.6's turning similar lap times to the 99 plus cars. It takes a consistent pointy end wheelman to perform equal to the 99 plus throughout a race.

ironically, it takes a "  consistent pointy end wheelman" to do it in a NB as well

[Tom Sager]

ironically, it takes a "  consistent pointy end wheelman" to do it in a NB as well

Yes and especially at Blackhawk.  A fart break will cost you 2 spots there. 

[SaulSpeedwell]

I guess where I was confused was that the Salisbury tuning was a pointy-end type of thing but I thought there really weren't any pointy-end 1.6 cars at this point. 

 

There are 1.6s still doing well at places other than the Nat'L Championships.  To the extent this thread is relevant BEYOND SM, I know that the diffs covered here are found in ITS, STU, FP, and other various track rats and Solo cars. 

[SaulSpeedwell]

I thought the 2002 still ran the Torsen. Was it a mid-year change?

 

You could very well be right, I just have never confirmed it so left it a little open.  Some sources claims the "TFS" (Tochigi-Fuji-Super) creeped in during 2002.  It may simply be confusion stemming from the diff being introduced in "2002" for the 2003 model year.  On balance, it appears to me that all or, at worst, nearly all 2002 cars have a T-2 Torsen.

[Jim Drago]

2001-2 torsen

03-05 Tochigi