4.875 / 5.12 Rear-End N/A gears
I know some people are interested in this.
I called SpeedSource about getting the MazdaComp ring and pinon 4.875 fitted to the N/A LSD rear end. They said $375 to lengthen gears to fit and then you have to install them in the rear end. I guess you have to load it right and a bunch of other stuff over my head to make sure they don't blow up, so I asked how much if we just send the entire pumpkin to you and have you install the gears into the rear end. Thats another $150. Plus parts to rebuild the entire rear diff, he said when it's all said and done 5.12's cost a customer around $600, excluding the cost of the gears. The cost of the 4.875's from mazdacomp is $281.40 While the cost of the 5.12's are $561.65 Hmm...decision's decisions, personally going with the 4.8's sounds pretty cost effective, basically 800 bucks for the whole shot...It would be better if I knew how to rebuild and install the gears into a rear end, I wonder how hard it'd be. Because for $656 thats a decent deal, when the 4.33's are 500 alone from racing beat. I wonder how useless 1st gear would be in the stock N/A tranny? Part No. 1312-27-110A Description RING AND PINION, 4.875 Notes Short pinion design. Fits 79-85 RX-7, 1994-01 Miata, RX-2, and RX-3 SP. Can also be lengthened to fit 86-91 RX-7 non turbo. |
Screw that! Just go to parts trader and find a chunk already set up with the gear you want for$300. Or you can buy the ring and pinion (used if possible). And have a local transmission or full service shop set it for you. Call a tranny shop and ask them how much to set the gears if you bring in the chunk. I bet it is hella cheaper than you where quoted.
Mike |
You've seen 2nd gen rear diffs setup with 4.88s on PartsTrader??????????????
PaulC |
Originally posted by Silkworm You've seen 2nd gen rear diffs setup with 4.88s on PartsTrader?????????????? PaulC I've never seen any 2nd gen diffs on parts trader but I've never really looked. I do see first gen diffs on there regularly though and have even bought one from there. I know it's not the same thing. ;) Mike |
Depending on the intended use of your car, a 5.12 may be a bit much. The 5.12 is intended to minimize the need to go to second gear and in the long run, may save you some shifts, thus helping longevity.
I have a few gear charts for the 4.88 and 5.12, I will attempt to post. Keep in mind, in my ITS car I have a .756 GTUs fifth gear. GearChart4.88: Gear 1 2 3 4 5 Final Ratios: 3.475 2.002 1.366 1.000 0.756 4.880 RPM Limit: 8500 Power @ Peak RPM: 190 Tire Size: 225/45 x 15 Tire Diameter: 22.97 in Tire Circumference: 72.16 in Gear Mph per 1000 RPM Mph @8500 RPM -------------------------------------------------------- 1 4.03 34 2 6.99 59 3 10.25 87 4 14.00 119 5 18.52 157 Mph RPM (in Gears) ------------------------------------------------- 1 2 3 4 5 ------------------------------------------------- 5 1241 715 488 357 270 10 2482 1430 975 714 540 15 3722 2145 1463 1071 810 20 4963 2859 1951 1428 1080 25 6204 3574 2439 1785 1350 30 7445 4289 2926 2142 1620 35 5004 3414 2499 1890 40 5719 3902 2856 2160 45 6434 4390 3214 2429 50 7148 4877 3571 2699 55 7863 5365 3928 2969 60 5853 4285 3239 65 6341 4642 3509 70 6828 4999 3779 75 7316 5356 4049 80 7804 5713 4319 85 8292 6070 4589 90 6427 4859 95 6784 5129 100 7141 5399 105 7498 5669 110 7855 5939 115 8212 6209 120 6479 125 6748 130 7018 135 7288 140 7558 145 7828 150 8098 155 8368 Gear Change RPM drop (change @190) RPM drop (change @8500) ------------------------------------------------------------- 1 -> 2 -81 (to 109) -3603 (to 4897) 2 -> 3 -60 (to 130) -2700 (to 5800) 3 -> 4 -51 (to 139) -2277 (to 6223) 4 -> 5 -46 (to 144) -2074 (to 6426) GearChart5.13 Gear 1 2 3 4 5 Final Ratios: 3.475 2.002 1.366 1.000 0.756 5.130 RPM Limit: 8500 Power @ Peak RPM: 190 Tire Size: 225/45 x 15 Tire Diameter: 22.97 in Tire Circumference: 72.16 in Gear Mph per 1000 RPM Mph @8500 RPM -------------------------------------------------------- 1 3.83 33 2 6.65 57 3 9.75 83 4 13.32 113 5 17.62 150 Mph RPM (in Gears) ------------------------------------------------- 1 2 3 4 5 ------------------------------------------------- 5 1304 751 513 375 284 10 2609 1503 1025 751 568 15 3913 2254 1538 1126 851 20 5217 3006 2051 1501 1135 25 6522 3757 2564 1877 1419 30 7826 4509 3076 2252 1703 35 5260 3589 2627 1986 40 6012 4102 3003 2270 45 6763 4615 3378 2554 50 7515 5127 3754 2838 55 8266 5640 4129 3121 60 6153 4504 3405 65 6666 4880 3689 70 7178 5255 3973 75 7691 5630 4257 80 8204 6006 4540 85 6381 4824 90 6756 5108 95 7132 5392 100 7507 5675 105 7882 5959 110 8258 6243 115 6527 120 6810 125 7094 130 7378 135 7662 140 7945 145 8229 Gear Change RPM drop (change @190) RPM drop (change @8500) ------------------------------------------------------------- 1 -> 2 -81 (to 109) -3603 (to 4897) 2 -> 3 -60 (to 130) -2700 (to 5800) 3 -> 4 -51 (to 139) -2277 (to 6223) 4 -> 5 -46 (to 144) -2074 (to 6426) Hopefully this will give you an idea of what rpms you will see with the respective gears. :bigthumb: |
Sorry but the spacing set up in the message screen will not transfer with the post. If anyone would like the charts emailed to them, just let me know. I can paste them into the body of the email, or attach them as a Word document. Your choice.
Sorry it didn't work. You may still be able to interpret the data, it's just a bit harder. You might also attempt to reconstruct the data by copying/pasting to your own Word document and going from there. Good luck. |
Are higher ratio gears legal in SP??
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No, according to my 99 Solo2 rule book.. Maybe the rules changed between 99 and now, but I doubt it :)
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I would apprecaite the chart.
Can you run it with MIATA transmission gear ratio's? Thanks John |
I don't think you can run the 5.12, but maybe the 4.88. The 5.12 will put you at about 145 at 8300 in 5th with the GTUs gearset. This setup works very well at tracks here in the Southeast. I know the 4.88 is more popular elsewhere, but here the 5.12 dominates. Isn't the Miata 5th gear like a .81 or .83? That may equate to too much rpm/not enough top speed.
Remember that the tightest ratios and lowest rear gear are not always the best combo. Having a setup that requires you to shift more is sometimes more costly on the stopwatch than having a bit less gear but saving a shift. John, I'll have to forward you the chart from home this evening. If you have all of the ratios for the Miata gears, I can plug them in and provide that info as well. LEGAL DISCLAIMER: IT racing does not permit the changing of ratios within the gear box. However, the GTUs box is a legal upgrade, and since the 5th gear is the only different ratio from the others, most guys just change 5th gears. I don't know about SOLO and the different class allowances, but in IT it's a no-no. |
did any company any low final drive gear for 2 gen TURBO. I am runing ITE (13B PP) in SCA. the only thing I can find is 4.3 from MAZDA comp. just wondering ??
the stock TII ratio is 4.1 |
the 5.12 and 4.88 should have the same installation "problems". I believe both of these ring and pinions are modified to fit the second gen N/A diff. I have seen many 5.12 setups and this seems to be the EP setup of choice. R&P are modified and then the installation is the same as any other R&P. Speedsource unfortunately gets a ton of money for their parts.
As for the turbo II diff the only other gear is a 4.33 available from Mazda. I believe this was an option on the turbo II and GTU cars. |
Originally posted by tims the 5.12 and 4.88 should have the same installation "problems". I believe both of these ring and pinions are modified to fit the second gen N/A diff..... R&P are modified and then the installation is the same as any other R&P. Speedsource unfortunately gets a ton of money for their parts. It's worth looking into. |
So the million dollar question is who is the machinist. I've talked to a friend that runs a BIG machine company and he didn't want to touch the project. Another fellow RX-7 racer / machiniat does his own but has snapped them too so it seems to be quite the little art to modifying the gear. You SW guys ought to know the source and how to cut out the middle man.
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So the million dollar question is who is the machinist. I've talked to a friend that runs a BIG machine company and he didn't want to touch the project. Another fellow RX-7 racer / machiniat does his own but has snapped them too so it seems to be quite the little art to modifying the gear. You SW guys ought to know the source and how to cut out the middle man. |
Originally posted by tims this is quite common with these modified R&P. the 5.12 needs a cooler and pump to keep it alive and would be recomended with the 4.88 also. this setup is a very short lived item. in racing time they are good for maybe one full season of racing. the machine work can be done by any competent machinist, but the setup and installation are the same as a stock R&P. And we must do without the cooler/pump setup, that was declared illegal in Fastrack over a year ago. I don't agree with it, but that doesn't change the legality. As to the machinist, it probably could be done by any talented individual, we just haven't found someone willing to take on the job. The setup alone to make the fixture would likely price you above simply having SS or ISC do it for you. |
Actually, I know many racers that have run the same gear set for many years, over 5 for one individual I can think of. |
4.88 and 5.12 gear Rx7 FC
Hi
If you still have them for sale ? What is your contact number? Very much interetsed.. My contact is 808 217 7371 I live in Hawaii Thanks Kyle Matsuoka |
If you know exactly what you want, as in how much the pinion needs to be lengthened, Gene Berg here in California are pretty experienced in how to do this properly: they make 5 speed conversions for air cooled VW applications.
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