I was wondering if anyone has thought about changing the differential on the 3IS to keep up with the 2IS's or even surpass them in terms of acceleration?

Since the 3IS's have the ISF Transmission, it has i believe a 2.9 differential ratio.

Though it might sound nice to have an ISF transmission in our 3IS's, I believe that our v6's
dont match up well with this transmission which then actually makes our acceleration slower
than the aggressively geared 2IS's.

What I was thinking about doing was getting a 2IS differential(carrier) and swapping it in my 3IS so my gear diff would increase would be from 2.9 to 4.0!

Anyone know if this would be a direct swap? ISF owners are doing it in their cars and I dont see a reason why it wouldnt work in ours.

 

I have to agree with this. The 6 speed in my GS matches up better with this engine than does the 8 speed. Especially in automatic mode the 8 speed isnt aggressive at all.

 

If these numbers are correct Lexus did change the ratios for the 8 speed in our cars ?!

 

Obviously 3.1 vs 4.0 is still a huge difference and 2.9 to 3.1 is not but I assumed they didn't change it all.

 

Okay so more precisely they changed the ratios for the LS 460 to a 3.1 final drive and this is the same they decided to use for our cars.

 

It is believed that Lexus made the gear ratios taller to have better mpg thus the reason why they went with a less aggressive gear setup for our 8speed 3IS's.

Was wondering if you or anyone that knows if a 3IS differential would be easily swapped out to a 2IS differential

 

Im sure it fits. You can be the judge of how easily.

 

Have you thought about using the 3IS250 differential? They have a shorter rear gear than the 3IS350.

I would imagine the mounting points of the differentials are the same between the IS250 & IS350, just confirm if the driveshaft is the same part# or at least use the sound mounting points.

 

All of this sounds good but you must realize that with the 3IS change in ratios over the 2IS was also a difference in transmission gear ratios. If you do the math the TOTAL gear ratio is very close to the same. Yes, a 2IS rear gear in a 3IS would make it much quicker at the loss on the top end. I am old school, when we changed a rear gear we also changed a small gear in the transmission running the speedometer to keep a true speed reading. Not sure how that works in todays electronic versus mechanical set up.