In the interest of increasing the versatility and high-speed fuel economy of my RX, I would like to swap the LO range gear and 4th and 5th gear sets from an SPFI D/R tranny into my Turbo D/R tranny.

 

Why? The SPFI's higher LO range would give more 'oomph' than mine, and the lower 5th gear would give longer legs on the highway (with city driving balanced by the lower 4th gear).

 

I like the FT4WD of my current gearbox vs. selectable 4WD, and supposedly the turbo units had stronger bearings, so a straight-up transmission swap isn't something I want to do. Also, my 1st, 2nd, and 3rd would remain their original ratios with the gear swap, so the acceleration from a stop would remain mostly the same; I'd just have to hold 3rd and 4th a little longer, and potentially downshift from 5th on steep inclines or for high-speed passing (rather than simply goosing the accelerator as I can currently).

 

Anybody have any experience with doing something like this? I'm mostly interested in sourcing the gears (or a donor gearbox with something broken other than my desired components) and whether there are any crazy differences between the units that may prevent simply sliding different gears into my gearbox.

Well, there is LOTS of information here but you will have to dig around for it. Several of us have done mods to the EA series trans. Although I haven't done exactly what you are talking about, I did swap a 3.9 Ring and Pinion from an XT6 donor trans in to my 3.7 F/T box. I also swapped 23 spline front stubs at the same time.

 

I have been through a couple of D/R boxes too. I just did the synchros on 1st and 2nd and I can tell you you'll need a press and a torch to get some of the gears swapped (not sure about 4th and 5th). Good luck and do document and share if you go forward. Here is a thread with some pics to get you started. As far as parts I would just source a donor trans. Might as well plan on doing ALL the seals while your at it.

 

RX Teardown

Edited December 2, 201213 yr by Crazyeights

all do-able. If you're not afraid of pulling the trans apart, swapping the low range and 5th gear are pretty easy. 4th is much more in-depth, as there's a bearing between 4th and 5th on both shafts. Also, I'm not 100% sure if the PT4WD lower gears will swap in place of FT4WD ones, I'd have to look again.

 

 

FWIW. I don't believe for a second that the turbo models are any stronger, I've been in and out of many subaru 5MTs (EA82t, EA82, XT6, couple EJs), they all look identical to me.

 

Also, you may not see an improvement in mpg with the taller gears and an EA82t. With the low compression and such, it may not have the power to maintain speed without leaning on the throttle pretty hard. The RX ratios were absolutely idiotic in my wagon behind an EJ22.....but the gains may not be much.