Automatic Gear Ratio change

[AceHeader-MT]

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

For reference, here's a video of an AT with 5.1 FD and Delicious E85 tune/kit.

Shift points are pretty good and still can drive on highway. Car is on 17" wheels with 235/40 tires.

Start video at 2:15ish and check tach. Only hit 5th gear on straight and speed is approx 200kmh

[ame="https://www.youtube.com/watch?v=zHM51jTFXu0"]3 22 '15 OTGP Time Attack Final - YouTube[/ame]

[FRS Justin]

Ok heres a quick run down on auto trans gearing. Its not like a manual where you have to gears running together to make a ratio, To change a autos gears you would need different clutch hubs, pinions, and sun gears. What is turning when you are in any certain gear is that gears clutch pack that has the "gearing" machined into the pack. basically everything would have to be machined new. Now this isn't a brz/frs trans but it will give you a idea of what Im talking about.
Go with a final drive gear 4.88 to 5.29 and you will be happy just remember the bigger the number the less top end so if you a light to light guy go 5.29 or 5.71 if you like running 140mph or more go 4.88 to 4.56. A little goes a long way in gearing. Call Mark at Spencer Fab in New Hampshire he can answer all your questions and set you up too. If your on the west coast call Weir Performance. I have done business with both and will say they are both stand up guys.

[SUB-FT86]

The automatics have a theoretical top speed of over 200 mph that is almost impossible to reach so a 4.88 or 5.29 fd drops it to about 160-170 mph which most of us will never reach anyways. This is all thanks to the 2 overdrives in the 6AT.

[KoolBRZ]

Originally Posted by AceHeader-MT

For reference, here's a video of an AT with 5.1 FD and Delicious E85 tune/kit.

Shift points are pretty good and still can drive on highway. Car is on 17" wheels with 235/40 tires.

Start video at 2:15ish and check tach. Only hit 5th gear on straight and speed is approx 200kmh

Wow, that driver pushes that car right to the edge. I had no idea an AT could be that fast, and that's without FI. It could be even faster with a supercharger.

[SUB-FT86]

I want to do something similar with mines like in that video above. And that video made me realize it's a good thing to get a 5.something FD plus e85.

[AceHeader-MT]

Originally Posted by KoolBRZ

Wow, that driver pushes that car right to the edge. I had no idea an AT could be that fast, and that's without FI. It could be even faster with a supercharger.

You made my day, thanks for the complements!

With a good gear ratio, good brakes (Essex) and good suspension (Racer-X) you never feel like you're on the limit.

The 5.1 change was one of the most substantial differences...besides Delicious and their E85 tune/kit.

[Toyota86.ir]

Originally Posted by KoolBRZ

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'!

with FD 5.71 we will smoke tires but it shift to gear 5 in 150km/h.
gear 5 and gear 6 in AT are so tall and the acceleration drop in gear 5.

Originally Posted by AceHeader-MT

For reference, here's a video of an AT with 5.1 FD and Delicious E85 tune/kit.

Shift points are pretty good and still can drive on highway. Car is on 17" wheels with 235/40 tires.

Start video at 2:15ish and check tach. Only hit 5th gear on straight and speed is approx 200kmh

Thank you

Originally Posted by FRS Justin

Ok heres a quick run down on auto trans gearing. Its not like a manual where you have to gears running together to make a ratio, To change a autos gears you would need different clutch hubs, pinions, and sun gears. What is turning when you are in any certain gear is that gears clutch pack that has the "gearing" machined into the pack. basically everything would have to be machined new. Now this isn't a brz/frs trans but it will give you a idea of what Im talking about.
Go with a final drive gear 4.88 to 5.29 and you will be happy just remember the bigger the number the less top end so if you a light to light guy go 5.29 or 5.71 if you like running 140mph or more go 4.88 to 4.56. A little goes a long way in gearing. Call Mark at Spencer Fab in New Hampshire he can answer all your questions and set you up too. If your on the west coast call Weir Performance. I have done business with both and will say they are both stand up guys.

Thank you , great info
i have 4.88 and i ordered it to Weir , robert at weir is responsive and nice.
we installed it after working above 18 hours and there is no noise .

Originally Posted by KoolBRZ

Wow, that driver pushes that car right to the edge. I had no idea an AT could be that fast, and that's without FI. It could be even faster with a supercharger.

i guess my AT GT86 (hks header E85 mike tune FD 4.88) be even faster than AT in video. my 0-100km/h record before FD swap is 6.6-6.7 seconds in sea level.

guys
let me time i will publish an Excel file for acceleration comparison of various FD on brz.

[SUB-FT86]

Originally Posted by AceHeader-MT

You made my day, thanks for the complements!

With a good gear ratio, good brakes (Essex) and good suspension (Racer-X) you never feel like you're on the limit.

The 5.1 change was one of the most substantial differences...besides Delicious and their E85 tune/kit.

Would you say that the 5.1 is streetable on a daily driver?

[AceHeader-MT]

Originally Posted by SUB-FT86

Would you say that the 5.1 is streetable on a daily driver?

That car is a daily driver with almost 100K on it. Cruising highway speeds in 6th are 130-160kmh between 3-4k rpm.

Stock tires are 225/45 Goodyear F1's. (used to have PSS 245/40)

Very comfortable.

[SUB-FT86]

If you put a 5.29 fd in a auto you will be almost at the same revs/mph in all gears as a 4.1 6MT while having a much more torquey 1-4 gear and delivering the same mpg as a 6MT.

http://www.grimmjeeper.com/gears.html

[Toyota86.ir]

My Summury about FD swap with AT and MT Transmission :

most street drag is between 20-110 miles and the best choice for AT is 4.88-5.29 and best choice for MT is 4.77-4.88
my choice for AT is 4.88 and for MT is 4.72

please see below, each cell number shows the percent of time reduction.
for example the AT 4.88 number in table is 5.2 at 170km/s. number 5.2 means if AT 4.1 reach 170km/s in 17 seconds then AT 4.88 reach 170km/h in 16.11 seconds.
16.11 is 5.2% lower than 17 seconds.




see other numbers in this excel :

http://toyota86.ir/wp-content/upload...1/FD-GR-T.xlsx

this is another useful excel i downloaded from this forum and uploaded again because google link was not available:
http://toyota86.ir/wp-content/upload...86-Ratios.xlsx

[FRS Justin]

Originally Posted by SUB-FT86

Would you say that the 5.1 is streetable on a daily driver?

Yes most definitely.. For my type of driving anyway....

[FRS Justin]

Originally Posted by Toyota86.ir

My Summury about FD swap with AT and MT Transmission :

most street drag is between 20-110 miles and the best choice for AT is 4.88-5.29 and best choice for MT is 4.77-4.88
my choice for AT is 4.88 and for MT is 4.72

please see below, each cell number shows the percent of time reduction.
for example the AT 4.88 number in table is 5.2 at 170km/s. number 5.2 means if AT 4.1 reach 170km/s in 17 seconds then AT 4.88 reach 170km/h in 16.11 seconds.
16.11 is 5.2% lower than 17 seconds.




see other numbers in this excel :

http://toyota86.ir/wp-content/upload...1/FD-GR-T.xlsx

this is another useful excel i downloaded from this forum and uploaded again because google link was not available:
http://toyota86.ir/wp-content/upload...86-Ratios.xlsx

In drag racing you want to run max rpm at the end of the 1/4 in 1:1 which is 5th gear. A 5.29 will not get you there unless you run a smaller tire. A drag only no street driving car would want a 5.71 ratio in 5th gear or a 4.56 max rpm in 4th gear. SO choose tire size then get the gearing

[SUB-FT86]

[ame="https://www.youtube.com/watch?v=XuXT5n-ds4A"]0-60 mph BRZ - YouTube[/ame]


I'm so in love with this guy's 6AT acceleration! It goes to show that 4.88 FD/Header/E85 and tune is perfect for me. I prefer a car that feels fast and revs quick vs just wanting a really fast car.