First of January, I completed my 2IS 4.08 differential swap on my 2021 IS350, truth is... I don't know if I like it.
To clarify before I get into the draggy numbers, I have bad tires, I am in Miami, FL, and I'm stock everything besides true dual + secondary cat delete.
Daily drivability the 2is diff feels the same as my 3is diff (I don't have the dhp so I have an open differential, 3.1 gearing) there is no apparent difference until you punch it.
During the first week of the installation you and the car have to get used to the new ratios, there will be harsh shifts at first but eventually the car will drive as smooth as it beforehand.
Part of the reason of creating this thread is because I don't see an improvement in performance, for years the lexus community has discussed that the 3is is slower in comparison to the 2is because of the gearing, with many people wanting to swap the differential. There are only two recorded swaps but none of them have gone in detail comparing numbers or performance/drivability. I took the risk and swapped it.
Here are my draggy numbers:

STOCK 3IS DIFF:
0-60:

https://ibb.co/H2xN3JX

1/8th Mile:

https://ibb.co/9HVV2dV

1/4th Mile:

https://ibb.co/C0VFH0G




AFTER DIFF SWAP
0-60:

https://ibb.co/yX28ygt

1/8th Mile:

https://ibb.co/KwpYWJm

1/4th mile:

(I still haven't been able to do a quarter-mile run with the new differential)

So there are the times, I feel like the times stayed the same or maybe got worse. In theory shouldn't I be running faster times? Thoughts?

 

To be clear, you did these measurements with traction off (10 sec hold) and in manual mode, right? For full performance regardless of diff, you have to be in that state, and shift up at redline. This is where it really is just up to math (and your tires), and the 4.08 diff should deliver.

Whenever I talked about this, it was more about the daily acceleration- this is where others complained it was funky.

 

Daily acceleration is completely fine and I can't even tell the difference when its in automatic mode and I'm doing city driving.
Also no, none of these tests had traction control off, tires aren't the best right now for me to do that, once I have better tires I will update this thread and show more draggy times.

 

Any updates?

 

I managed to get the 0-60 to 4.9 lowest. I think the 3.76 diff is better for the 8-speed, 4.08 is too aggressive for 8 gears and it decreases the top end. The 3.76 is the best median. Still have yet to get better tires (sorry lmfao) but once I do I will do more testing.

 

Holy crap, 4.9! That is excellent stuff.

 

Any more notes? Before I pull the trigger on this myself

 

Whats is the cruising rpm for 65 mph and 80 mph with the 4.08 diff?

 

70mph with a driven wheel diam of 24.75" on the highest gear of the 8-speed used in the 2020+ RWD 350:

• With the original final drive ratio of 3.13 (stock), the RPM is approximately 2,038.
• With the swapped final drive ratio of 4.08, the RPM increases to approximately 2,657.

 

Fenny, any updates?