This was an idea I’ve had in mind for a while now.

As we’re all aware, a lot of new cars are coming out with 8, 9 and 10 speed transmissions and they are proven to shift much faster than any 5 or 6 speed in a car of its previous generation. I’ve seen videos and read about the ISF with the rear differential swap from the IS350 and the performance gains it provides. So the whole idea is (completely ignoring cost/labor for now, just hypothetically speaking), would an 8 speed and ECU swap from a 3IS IS350 improve our cars performance on track or in the ¼ mile? Would it also give fuel economy gains? Has anyone else thought of this? The 3IS IS350 has the same engine as the 2IS, but are connections to the driveshaft and engine similar? Are the transmission units themselves completely different? Am I insane?

Even if it is possible the rear gears would have to be swapped because there would be very minimal traction in first gear. (1st in 8 speed is 4.5XX:1, IS350 rear gear is 4.10, unless I am completely misunderstood, forgive my ignorance) And if it is possible, it would allow the gearbox to be used completely manually instead of the gear limiters on the 6 speed (which is something I've seen a lot of people wanting, and for very good reason) because the ECUs are programmed differently. Just curious to hear what other more experienced people think of this. I am not considering doing this by any means even if it is possible (don't even have my car yet lol) but I just want to hear what people think.

 

IIRC, the 2IS is faster off the line than the 3IS because of a more aggressive 1st gear. With an 8 speed transmission I'm sure it'll greatly benefit fuel economy. As far as being possible I wouldn't know.

 

I know that the 2014s are geared smaller in the back. People with the 3IS are getting the gearing from 2IS to make them faster. The lower gearing gives them better mileage.

 

Didn't know this. The reason I had this idea was mainly as an excuse to swap out the transmission ECUs because the 8 speed one has full manual mode where you actually control the shifts without a gear limiter. The 'manual' mode actually works okay (its definitely pretty bad, but okay for something that doesn't allow complete control) for downshifts, but upshifting is a complete mess lol.