Differential

Last updated: November 3, 2004

• Gear Sets
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• Drive Shaft

Rotary Performance

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Date: Fri, 07 Aug 1998 16:06:22 -0500
From: Trey Cobb (trey@rx-7.com)

Now, Brad Barber once told me once that creativity is the art of hiding your sources so lets see if I can be very creative in my answers:

1) Manufacture: A Company that specializes in Custom Gearbox manufacturing (sorry)

2) Material Used: Metal :-) It's basically the same material Mazda uses, nothing exotic. It's quality material though, otherwise we wouldn't offer it.

3) Pricing: $699/ea normal price. Secure 5 orders and the price is $650/ea. Secure 10 orders and the price will be $599/ea.

To be safe I'll say delivery time is 4-6 weeks. It's extremely important to have this installed by an EXPERIENCED mechanic. If it's installed incorrectly, it will damage the ring and pinion.

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Date: Wed, 21 Apr 1999 12:32:45 -0400 (EDT)
From: Wael El-Dasher (wael.el-dasher@yale.edu)

I have the RZ spec ring and pinion. Its a Mazda part so fitment is not a worry. It will involve opening your differential ofcoarse. I put the Mazdaspeed 2 way LSD and all new shims and bearings so the overall cost was high and its hard to tell the effect of only the ring and pinion alone. As far as the results...The 4.30 ring and pinion is great. I ofcoarse did not take any measurable data to support my butt dyno, my opinions are just that, opinions.

When you take your ring and pinion off, look at the wear. make sure its even. ie the wear should be the same on the outside of the gear's tooth to the inside of the tooth.

I also found excessive play in my differential when I took the drive shaft off, it was out of tolerance of the factory spec acceptable play, so I assumed it was the stock ring and pinion, I was mistaken, but that's whole different story. So try to remmember to check for play when you take the drive shaft off.

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The RS-R (later Japan-spec special edition) 4.3 ring and pinion set is available from Cork Sport for $549. I think this is what Wael has. --Steve

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Date: Thu, 07 Oct 1999 16:42:55 +0000
From: Wael El-Dasher (wael.el-dasher@efini.net)

> I understand why people don't go for the usual 4.30 gearset (why bother
> for a 5% reduction) but Rotary Performance lists a 4.77 set (16%
> reduction).  Sure your cruise rpms would go from 3,000 at 80mph to about
> 3,490, but I think thats well inside the working range of rotary.

I installed the 4.33 ring and pinion and it does make a difference. I bought them and just kept them a side until I got the Mazdaspeed LSD, and made a project out of it. I would guess the 4.77 ring and pinion would be most beneficial for the drag racing crowd, but with only a jump to 4.33 I can tell you that the cruising rpm jumps up quite a bit, just enough to make anyone who cruises or drives on the highway often on a daily basis to not consider it, but if you do not mind your turbos alway spooling and ready then it is a very nice thing to have as the car slingshots on the highway past traffic (or out of trouble as is mostly the case).

It is an upgrade that, as you said, is apparent from the seat of the pants. Around town and slow traffic the car is also more alert off the line. Dr. Ed Kim and Ryan Schlagheck both drove my car, I would be interested to hear from them their opinions as I surely got used to my car driving this way and probably forgot what the stock 4.10 feels like. I do remember Ryan saying that he was surprised on the highway that he didn't have to downshift to get the power, that it was immediate and quick. But he has been driving a non sequential for a while and perhaps he forgot what the sequential felt like too...I am rambling on now. For those who don't know this tid-bit, the 4.33 ring and pinion is a Mazda OEM part, its for the RZ spec rx-7 in Japan.

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From: Rick Zehr (rzehr@pacbell.net)
Date: October 25, 2000

I just had a 4.30 gear set installed in my `93 Touring Automatic, and thought I'd report on the results. Sorry for the long post, but I thought I'd cover the topic once and for all...

Warning - Personal Opinion Follows:

Opinion ON

IMHO, this should be the first mod for any Automatic FD, for reasons I'll describe below. Opinion OFF

OK, now the facts - compare the gear ratios and rear-end ratio in the 5-speed, vs. the automatic.

Higher numbers are 'lower' gears, smaller numbers are 'higher' gears.

                5-speed         Stock
                Manual          Auto
Diff. Ratio      4.09           3.91

Trans.  1        3.48           3.03
Gear    2        2.02           1.62
        3        1.39           1.00
        4        1.00           0.69
        5        0.72

So to get the overall gear ratio (ratio of engine revolutions to rear-wheel revolutions), we multiply the ratio of the gear times the ratio of the differential, and get the following table.

                4.09            3.91            4.30
                Manual          Auto            Auto

Gear    1        14.2           11.8            13.0
Ratio   2         8.2            6.3             7.0
        3         5.7            3.9             4.3
        4         4.1           2.71             2.98
        5         2.94

If you graph this in a spreadsheet (See below), it is very obvious that the stock automatic suffers compared to a 5-speed in several ways:

• Its lowest gear (first) is much higher than the manual - almost 20% higher a ratio. This makes for a slow start, because the engine is fighting too high a gear for first.
  
  
• Its highest gear (4) is almost 7% longer than the highest gear on a manual. While this makes for relaxed and quiet cruising, it also makes for mediocre acceleration on the highway.
  
  
• Second and third gears are each much higher than the corresponding manual gear at any given speed. This means the car is sluggish in traffic.

The alternative for an automatic (or for a manual, just less change) is to replace the ring and pinion gears in the differential with a different 'lower' ratio set. Mazda supplies a 4.30 gear set (43 teeth on the ring, and 10 on the pinion), and all the usual vendors carry this gear.

This lowers the ratio of all four gears by 10% (4.30/3.91 = 110%), and has the following effects:

• First gear becomes much closer to that of a 5-speed, giving better acceleration from a stop.
  
  
• Second gear becomes excellent in traffic - it fits just between 2nd and 3rd on a 5-speed. It only goes to 65 mph at 6000rpm instead of to 72, but it is much more useful (second was too high), and, being lower, works well to allow third gear to be useful, instead of just another sluggish gear that goes to 120mph. Third now fits in the middle of 3rd and 4th on a 5-speed, and is more useful than it was for suburban driving.
  
  
• Fourth gear is 10% lower, and this gives better acceleration on the highway, at the expense of more rpms at any given speed. With the stock diff, my car ran 2800 at 80mph. With the 4.30, it runs 3100rpm at 80, compared to a 5-peed, which is closer to 3050.

  The top speed of the car is probably not affected, since fourth gear still gives 26mph per 1000rpm, and so it should still be able to reach the same speed, since wind resistance is the major retarding force, and it would be running 6000rpm at 156mph - still right in the peak power band.
  
  

• Overall, the car feels much 'lighter' - the stock automatic just isn't very peppy, and most performance improvements are only effective at high rpms, which you can't use because of the high gears - you can't often go fast enough to hit 6000rpm in third...
  
  
• Compared to other performance options, this is effective even at low rpm - you get 10% more torque even at 1500 rpm. Compare this to 'breathing' performance enhancements, which often reduce power at the low rpm you really use in 99% of real-life driving.
  
  
• And then there is the single negative: my speedometer now reads 10% high - at indicated 80, I am really only going 72. But hey, this makes you feel like you are even faster, and when you drive down the road at 80 all the time, your girlfriend will be impressed 6^)

Installation requires that the diff be removed, because you have to re-shim and adjust the bearings, even if you don't replace them. This requires special Mazda shims, of course.

Prices for the gearset range from $474 (Racing Beat) to $563 (Mazdatrix). I believe that these are all the same Mazda part, which will work in either manual or auto cars of any year.

This would be a really good opportunity to replace the bearings and the seals, at a cost of just under $200 at Mazda prices. You could also replace the diff bushings at this time, if there is any slop in them (I didn't).

I had the work done by C2 Automotive in Oakland, CA, and am pleased with the results and the service. William drives a CYM R1, tells me that he has done alignment on M2's racing cars, and he obviously works on a lot of FDs (two in the lot when I was there). (510-272-9869) He charged me for 7 hours at $70, located the needed bits and pieces and istalled it all in one day (aside from the ring and pinion which I supplied).

So, for me, the bottom line is that for comparable money I could have got a couple of other performance pieces - say an intake and catback, but probably would not have got 10% more peak hp and torque, and certainly not 10% at all rpm ranges, and no way 10% more on top of any future performance improvements I make later.

Further, this is the only available performance tweak that makes NO additional noise. Even a downpipe adds to the noise level, and an intake unleashes a whole barnyard of new noises under the hood.

So, for all automatic FD owners, I suggest making this your first performance tweak. For 5-speeds, it's harder to justify - only a 5% difference, but it is 5% times your total torque, however high that might someday be...

				Ratios
Company	Product Description	Price	Gear		45/11		43/11	43/10
Mazdatrix	RING & PINION 4.30 93-ON	$563.40		Manual	4.09	Automatic	3.91	4.30
CorkSport	J-Spec 4.3 Ring and Pinion Set	$549.00	1st	3.48	14.2	3.03	11.8	13.0
Rotary Performance	4.30 Final Drive Ring and Pinion Set	$499.00	2nd	2.02	8.2	1.62	6.3	7.0
Racing Beat	Ring & Pinion Gears 4.30	$474.00	3rd	1.39	5.7	1.00	3.9	4.3
			4th	1.00	4.1	0.69	2.71	2.98
			5th	0.72	2.94

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From: Doug Underwood (Dunder@aol.com)
Date: October 25, 2000

I'm not doubting any of your results w/ the gear changeout, but the reason an auto always has a lower overall gear ratio for a given gear (diff gear taken into account or now) is the torque multiplication from the torque converter.

That said, it seems like a pretty obvious upgrade - more benefit (10% lower gearing) to an auto than a 5 speed (5% reduction)

Differential Mounts