Unfortunately the EJ and K3 transmissions are not interchangeable,
as the bellhousings and starter positions are different.
END OF EDIT
So I think I have found a theoretical winner. As MR_Gormsby said, all of the EJ/K3 transmissions are basically the same (only difference being in 4th and 5th gear on some models), apart from the gear ratios.
4th: 0.917 (0.865)
5th: 0.750 (0.707)
So far I’ve found there to be 2 factory ratios for these boxes: 4.267 and 4.500
But then I stumbled upon a box from a Mira L250 (EJ-VE):
Even though the gears are a bit shorter, with the longer final drive this
makes this the longest geared box I have found that should fit an EJ/K3.
Bellow it is compared with the longest EJ-DE/K3 variation from a L700 Mira.
Mira L250 box
Mira L700 box
Here for a comparison is the 4sp auto, the only factory option on the K3-VET
As you can see, being a 4 speed the gears are horrendously long. I can’t
imagine how sluggish that must feel even with the turbo engine.
So to close this up then, the best option gear wise looks like to be the L250 box, as anything shorter wouldn’t employ the full torque potential of the turbo engine in my opinion. Also it should be the best for economy since the cruising RPM will be always lower. There is a but though.
Why doesn’t the L250 have the same box as the EJ-DE ones? For example: post 2004 sirions that have the K3-VE still have the same box as the M100/101 ones.
Does that mean that this box is an “updated” version of the EJ/K3 one?
Why would they put the longest geared box in the smallest and least powerful car (Although the L7 Mira also had the longest variant of it’s box)?
PS: this has become quite a bigger write-up than i imagined, sorry if it’s too long for somebody.