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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain. |
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11-21-2015, 11:57 AM | #1 |
Mike Tune HKS E85 FD 4.88
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Automatic Gear Ratio change
Hi guys
I have AT GT86 and after FD swap 4.88 i am thinking about changing Gear ratio in my AT gearbox. maybe it seems dummy idea but i should add there is no MT GT86 for shopping in my country. Is there any after market company for changing gear ratio of AT gearbox? AT gear ratio is : 3.538 2.06 1.404 0.713 my idea : 3.50 2.50 1.80 1.35 1 |
11-21-2015, 07:14 PM | #2 |
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Changing ratios in an AT is probably not an option unless you have thousands of $'s.
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11-21-2015, 10:09 PM | #3 | |
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I=3.538, II=2.060, III=1.104, IV=1.00, V=0.713, VI=0.582 All the ratios you want to change are going to rev higher at a lower speed, If that's all you want, then why not just change your FD to 5.29, or even 5.71?
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11-21-2015, 10:25 PM | #4 |
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Change your final drive. Much easier and will get you the same results. Maybe not down to the number, but close enough where no one would know the difference.
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11-21-2015, 11:07 PM | #5 |
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OP, I don't think anyone makes gear sets for the automatic. Other issue is no one (to my knowledge) is capable of tuning the transmission control unit, which could be a huge problem if the computer is expecting stock gear ratios for any of its calculations.
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The Following User Says Thank You to PantsDants For This Useful Post: | Toyota86.ir (11-22-2015) |
11-22-2015, 12:19 AM | #6 | ||||
Mike Tune HKS E85 FD 4.88
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I have no idea about affecting closer gear on TCU. |
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11-22-2015, 01:30 AM | #7 |
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Your shifting rpms will be the same as a close ratio, with the 5.71 FD, but without the transmission actually being a close ratio. The higher the number FD, the closer your shift points become. It also takes some of the strain off your FD, transmission, and engine, and puts it on your axles and tires.
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11-22-2015, 01:51 AM | #8 | |
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The Following User Says Thank You to PantsDants For This Useful Post: | Toyota86.ir (11-22-2015) |
11-22-2015, 06:22 AM | #9 |
Mike Tune HKS E85 FD 4.88
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I think FD 5.71 make gear 1 so aggressive . Below are Approximate numbers :
5.71 * 3.538 = 20 vs 3.5 * 4.88 = 17 5.71 * 2.060 = 12 vs 2.5 * 4.88 = 13 5.71 * 1.404 = 8 vs 1.8 * 4.88 = 10 5.71 * 1 .000 = 6 vs 1.34*4.88 = 7 5.71 * 0.730 = 4 vs 1 * 4.88 = 5 Gear 1 20 vs 17 Gear 2 12 vs 13 Gear 3 8 vs 10 Gear 4 6 vs 7 Gear 5 4 vs 5 Then as pantsdants mentioned we could use gear 6 for economy |
11-22-2015, 06:10 PM | #10 |
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AT's are not as simple to change ratios in. You have to change a lot of parts that do not exist.
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11-22-2015, 09:06 PM | #11 |
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What about installing a Gear Vendor Under/Overdrive? It installs on the tailshaft, so would require a shortened driveshaft. But it's outside the transmission. An Overdrive would give decent highway mpg, but in normal mode with a 5.71 FD it would really scream.
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11-22-2015, 09:20 PM | #12 |
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I want to be the first guy that tried the 5.29 fd on the auto. A 29% increase sounds crazy!
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11-23-2015, 12:06 AM | #13 |
Mike Tune HKS E85 FD 4.88
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Thank you guys
It seems changing AT gears is not logical and I should try to buy manual transmission GT 86 for the next year. |
11-23-2015, 02:39 AM | #14 |
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Nooooooo
With an AT, and a 5.71 FD you could probably leave rubber in the first 5 gears, and get sideways in the first 4. Of course you'll still only be going about 30 mph, but those tires would be smokin'!
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