Automatic Gear Ratio change

[Toyota86.ir]

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

[FirestormFRS]

Changing ratios in an AT is probably not an option unless you have thousands of $'s.

[KoolBRZ]

Originally Posted by Toyota86.ir

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

The Auto has the following ratios;
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?

[Dustin]

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.

[PantsDants]

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.

[Toyota86.ir]

Originally Posted by FirestormFRS

Changing ratios in an AT is probably not an option unless you have thousands of $'s.

how much ?

Originally Posted by KoolBRZ

The Auto has the following ratios;
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?

FD 4.88 is good , in my mind close ratio gears give better result than upgrading FD 4.88 to FD 5.71 because gear 1 is more usable and after shifting to next gear we loss less torque. shifting 7400rpm to 5500rpm is better than 7400rpm to 4800rpm.

Originally Posted by Dustin

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.

i have no experience with close gears but in mathematics tell me close gears are better than higher FD.

Originally Posted by PantsDants

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.

MFactory and Cusco make close gear for MT but i did not find any close ratio kit for AT.

I have no idea about affecting closer gear on TCU.

[KoolBRZ]

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.

[PantsDants]

Originally Posted by KoolBRZ

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.

The purpose of changing the gears in the transmission is to change them relative to each other. This will change how much the RPMs drop/rise between shifts. It's easier to figure out where you're going to land in the rev range after a shift if the change in RPM is consistent between gears. Another benefit could be to make your 6th gear really tall for cruising but make your other gears shorter for better acceleration.

[Toyota86.ir]

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

[FirestormFRS]

AT's are not as simple to change ratios in. You have to change a lot of parts that do not exist.

[KoolBRZ]

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.

[SUB-FT86]

I want to be the first guy that tried the 5.29 fd on the auto. A 29% increase sounds crazy!

[Toyota86.ir]

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.

[KoolBRZ]

Originally Posted by Toyota86.ir

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.

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'!