For one, the ECU can't be cracked.Whoa, what is everyone so scared about? This kind of attitude is what keeps us with no modifications for our car or improvements if you don't let anyone explore. To the comment that it would be even more difficult to mate the 350 to the 250's manual then it's automatic? I completely disagree? Why would it be more difficult for the computer to work with a transmission that requires no computer to work (manual operation) then with an auto it isn't designed for? Here's another question for you guys. Do you really think that in the factory lexus has a different body for the 250, 350, is-f, or that they are determined during production as to what they will be fitted with? This platform is very interchangeable and as I research I learn this more and more. It seems car companies are getting smarter with interchangeable parts to lower costs which in turn gives us more options. Here would be a good start, IS350 complete engine out of a wreck (motor, harness, fuel injection system, computer, everything). Transplanting that, and assuming it bolts up to the IS250 manual transmission (which it should considering it has the same bell housing). You should be able to get engine to run even if it thinks the transmission is missing. From that point you would have the joy of getting someone to crack the computer and disable the various features your car won't have. Have fun, if you don't try it, someone else will; shoot i'd love to the first to swap it. Watch out IS-F for the 350 manuals!
They haven't even cracked most of the functions on the Supra ECU and that car is over 15 years old at this point...and the ECU on the IS is -way- more complex.
Many of the functions of the ECU are physically burned onto the PROMS so you'd need an electron microscope to even read the programming to begin with, before you even thought about how to change it. Then you'll need to crack the encryption that nobody has touched in all the years toyota has been doing it. Then you'll need to not tell anyone to avoid the DMCA lawsuit from Toyota.
So the engine will NOT run properly, probably not even at all, when it noticed half the powertrain it's expecting to help control doesn't exist.
For another, the cost to do the swap will be considerably more than just swapping the car for one that COMES WITH THE ENGINE TO BEGIN WITH.
And for a third, if the manual was capable of holding the power, and was simple to swap, then Lexus would be offering it as an option in the first place.
The fact they don't strongly suggests you'll kill the transmission even in the unlikely event you got the engine to even run without a transmission it's looking for.
And then there's still the fact the ECU would also be looking for the missing VDIM components too.
Seriously, the reason everyone is against it is it's a really dumb idea that simply won't work.
Oh, and the IS-F -does- have a different body. That's why the fenders and other parts don't interchange. The IS-F engine is larger so they had to make room for it.
Oh, and last I knew, the engine alone was over 10k...I'm sure it'd be less from a wreck, but probably not a TON less, certainly not the full powertrain. That's not counting labor or probably most of the wiring and accessories you'd need too.
Whereas the 250->350 cost difference is like 3-5k.