That-Guy

iTrader: (1)

supraforums has quite a few threads with such info i believe, just a matter of searching.

tonysc400

oh i searched ...just trying to see who out here had experiences of a good match gear ratio if you have a 2jzgte auto in a sc400 or 300...i will convert to single turbo first then try out the stock sc400 rear(3.92) and see if i like it..if not i will def go with a mk4 auto tt rear end and call it a day.

luxrysupra

if you look under the hood on the firewall it will tell you wether or not the rear end is torsen or open diff,that is if your taking your new rear end out of the supra. on the firewall there is a tag that says trans/axle: letter#letter, the letter will tell wich one it has. A stands for open diff and B stands for torsen LSD and the # stands for the ratio wich is aproximatly 01=4.08 02=3.76 03=3.27 so you want one that comes out of a car that says B02B on the tag. that will give you a torsen 3.76:1 LSD. hope that helps u some.

tonysc400

helps alot..great info

WhiteGsr

iTrader: (3)

Alright let me get this straight the 97 SC4 has a 3.26 rear end but the 96's and below had a 3.92 rear end?

The 98 Supra auto TT has a 3.77 torsen LSD rear end?

The bigger the number the shorter the gear hence more bottom end gain but you'll have top end lose?

Sorry for the ignorance I'm a newbie

tonysc400

yup the bigger the gear the shorter the gear..better pick up off the line but no TOP end

WhiteGsr

iTrader: (3)

So what gear ratio does a 98 supra auto tt diff have?

What ratio does a 97 SC4 diff have?

tonysc400

dont quote me on this but i think the 97 sc400 has 3.26? and the supra auto tt is 3.77

WhiteGsr

iTrader: (3)

Thanks Tony... Can someone confirm this?

tonysc400

97-00 SC400 3.266


92-97 SC300
6 cyl, AT (4.27 ratio)
6 cyl, MT (4.08 ratio)

98-00 SC300
6 cyl, AT (4.27 ratio)

92-96 SC400
8 cyl (3.92 ratio)

97-00 SC400
8 cyl (3.266 ratio)

92-96 MKIV Supra

w/o turbo; (4.27 ratio) Limited Slip
w/o turbo; (4.27 ratio)
w/turbo, MT (3.133 ratio) Limited Slip
w/turbo, AT (3.769 ratio) Limited Slip

97-98 MKIV Supra
w/o turbo; (4.08 ratio) Limited Slip
w/o turbo; (4.08 ratio)
w/turbo, MT (3.133 ratio) Limited Slip
w/turbo, AT (3.769 ratio)
w/turbo, AT (3.769 ratio) Limited Slip

WhiteGsr

iTrader: (3)

thanks man!!! Where'd you find such info?

WhiteGsr

iTrader: (3)

alright check this out, I have the 98 auto tt rear diff in. My speedo reads way slow. For those of you that have this diff too on a 97 sc400, when your going 65 what does the speedo say also at 45 what does the speedo say?

tonysc400

i'm actually putting in the same rear but a 94 auto tt rear which should be the same ratio into my sc400 jdm 2jzgte aristo swap..what engine do you have in your car?

aliga

iTrader: (147)

97 sc4 does not have 3.26

Blizzy

iTrader: (-1)

As was mentioned, your speedometer will read incorrectly when you alter the rear end gearing. To fix this, you will either need a "Yellow Box" or you could dabble with the circuitry yourself and build a DIY pulse width modulator.

In a turbo application, the main factor to consider when making a gearing choice is engine load. When the engine is under higher load, the motor will be using more fuel. When the engine is using more fuel, more exhaust gases will be being expelled. When more exhaust gas is being expelled, more force will be applied to the turbine. More force applied to the turbine means a wider powerband under boost.

A lower-numbered rear gear will increase engine load in every gear, although this effect can be overdone. In general, the standard convention is to choose a rear gear that will put your total first gear ratio between 10:1 and 11:1. For the stock 4AT (Gear 1 = 2.804), a total first gear ratio of 10:1 to 11:1 would be achieved with a rear gear of 3.57-3.92.

Choosing gearing on the high side of that range will put more torque to the road in any given gear. In a non-turbo application, this is an important factor to consider in terms of performance. Thus, in the 92-97 SC400, the Toyota engineers chose a gearing on the high side of the range at 3.92. In the slower, smoother, more luxurious 90-97 LS400, the Toyota engineers chose a gearing on the low side of the rage at 3.62.

Choosing a gearing on the low side of that range will put more load on the engine in any given gear. In a turbo application, this is an important factor to consider for performance. In the Auto TT Supra, the Toyota engineers went with a 3.76 ratio to try and optimize both engine load and torque output. Going lower than 3.76 will increase engine load and effectively widen the power band at the expense of responsiveness from decreasing the torque to the road in every gear. Going higher than 3.76 will increase torque output and responsiveness at the expense of effectively narrowing the power band from decreasing engine load in every gear.

For the stock 4AT:
- A 3.26 ratio is lower than would be preferred. The car would be rather sluggish even though the boost curve would become wider.
- The 3.62 ratio from the LS400 would be on the low side of desirable, but with the different geometry to the pumpkin, you would have to fully swap the internals into your SC housing and find an LSD (lots of work).
- The 3.76 ratio from the TT Auto is in the middle of the desirable range, but having been designed to mate with a different driveshaft, you would have to swap companion flanges from your SC4 differential to the TT differential (not a lot of work).
- The 3.92 ratio from the SC400 is on the high side of the desirable range, but lacking an LSD you would need to swap one in (lots of work).
- Anything above 3.92 is higher than the desirable range, sacrificing too much width to the boost curve at the expense of responsive torque production. This would be positive for performance in a non-turbo application, but not in a turbo application.