Originally Posted by WhiteGsr

So the 97 SC4 has a 3.92 rear end? I am seeing both 3.26, and 3.92 on different threads, which is it really?

Originally Posted by YeA 2jZ

Do you have any info on the GS400/430 rear end some of the supra guys are running them in there turbo apps i am thinking of doing the same.

Originally Posted by 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

Originally Posted by Blizzy

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.

Originally Posted by Blizzy

If you have a 4AT in your SC400 (92-97), then you have a 3.92 rear end. If you have a 5AT in your SC400 (98-00), then you have a 3.26 rear end.



The 98+ SC400/GS400/GS430 rear end with the 3.26 ratio is altogether identical to the 97- SC400/SC300 rear end with the exception of the gearing. The companion flange is the same. The mounting points are identical.

If you are running or will be running a V160, then the Lexus 3.26 differential offers the possibility of being used instead of the TT 6MT diffferential since both offer similar gearing. Your would need to modify the Getrag driveshaft to include the rear section from a stock SC300/SC400, but you have to modify the Getrag driveshaft to work with the SC regardless.

If you are running a W58 or R154, then the 3.26 would not be a bad option either. The 3.26 ratio would offer a total first gear ratio of ~10.6:1 with the R154 (3.25:1 first gear) and ~10.7:1 with a W58 (3.29:1 first gear). This value is more well centered in the 10-11:1 range that is conventionally considered to be ideal. While the 3.76:1 ratio of the TT Auto would put more torque to the road, the 3.26:1 ratio of the 98+ Lexus rear gear would increase engine load to effectively widen the power band under boost.

In any event, the 98+ Lexus differential would require you to swap in an LSD to have slip protection. Any LSD unit for the TT Auto or NA MKIV Supra would swap in.

For reference, I have a Torsen LSD swapped into a 4.27 SC300 4AT differential on my SC400 with an R154. The total first gear ratio is ~13.9:1. This is an incredibly fun combination for a non-turbo car since tire-shredding torque is available in first gear in the car's current n/a state; but, this would be a bad idea for a turbo car since engine load in minimized, especially in the lower gears. I imagine building any boost in first gear with such a short ratio would be a challenge. Once supercharged, the car should come alive even more than it already has.

Originally Posted by sucessr1

I'm planning on doing a 2jzgte swap into my sc300 with an R154 is the supra 3.76 TT LSD a good option????

Originally Posted by Kris9884

I love the 3.26, I'm at about 2600 at 70 MPH.. But down low is lame.... Depends what you want.