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Premium Member
04 2.5XT 4EAT
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38 Posts
Discussion Starter #1
I was wounder if anyone knew what the max wheel horsepower the 4EAT could handle or an estimate.
 

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2006 Forester XT Limited 4EAT
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2,000 Posts
It really depends on how you drive it. There are some with 350-400whp woth no problems. If you brake boost @ 250 all the time you are going to kill it.
I should make ~350, but won't be brake boosting.
I'm confident in the 4EAT's ability to handle up to 400.
 

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2001 Forester Slushbox
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1,777 Posts
I've seen 400hp as the max stock I believe.
Hotrod guys will chime in.
 

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none none
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8,844 Posts
It will hold up to most stock location turbos you would use on a daily driver. Its going to mostly depend on how you drive it.

There is an issue however with some of them failing at the front diff casing, possibly due to the TC overheating or something. You can see it by a crack around the front axles.

It can probably hold as much or maybe even more than a completely stock 5mt, however theres not much that can be done in terms of upgrades. Definitely put an ATF cooler on if you're going to be running higher power or running it hard at all.
 

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2004 Forester XT Premium 4EAT
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29,449 Posts
Horsepower doesn't kill transmissions, torque does...
 

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Premium Member
04 2.5XT 4EAT
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38 Posts
Discussion Starter #6
well doesn't seem like holding the horsepower will be a problem. Are there any other supporting mods that would benefit the life and reliability of the transmission other then an ATF cooler?
 

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2008 XT Sports
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179 Posts
Theres quite a bit you can do. See here:

Subaru Auto Trans Parts

I heard getting an added cooler, switching to fully synthetic fluid, and getting a valve body upgrade are your best upgrades. If you want to build more boost off the line then an upgraded TC would be helpful..

--yamsta
 

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2019 Crosstrek 2018 XT
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14,377 Posts
I heard getting an added cooler, switching to fully synthetic fluid, and getting a valve body upgrade are your best upgrades. If you want to build more boost off the line then an upgraded TC would be helpful..

--yamsta
If pliad is right then really a cooler and Synthetic ATF won't make much difference in preventing failure. The extra heat a 400 HP develops is not gonna be much bc you can't keep dumping HP into the thing for longer than 15 seconds at a time. Now if you are gonna use 400 WHP to go up a 5,000 climb with WOT...yea.

And the syn ATF I used in my 2001 Sentra SE didn't hold up any better than non Syn...confirmed by multiple Used Oil Analysis.
 

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none none
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Yeah there aren't really any upgrades for the FXT direct control 4eat, only the old style. All you can really do is run a tranny cooler and change the fluid regularly, unless you want to go with a fully build transmission but thats getting to 6speed swap $$.
 

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2005 Forester XT 4eat
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4,583 Posts
The case is designed to split apart and send shards out, killing the driver when 450ft-lbs is exceeded in order to protect the engine.

I forget who it was, but someone had a 4eat diff come apart while accelerating hard over some bumpy pavement. I think the excessive wheel bounce and spin sent shocks through the front diff. This was at stock or stage 2 power. So you can do a lot of damage even at stock levels.
 

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2006 Forester XT Limited 4EAT
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2,000 Posts
Just maimed. The thinking is that we have it so much easier than all the huge left calf MT drivers that we should at least have the real threat of punishment hung over our heads....
 

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Premium Member
04 2.5XT 4EAT
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38 Posts
Discussion Starter #16
Since there are many different situations in which the 4EAT can hold the power or blow up. what are some dyno numbers people are making with the 4EAT and has it remained reliable?
 

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04 2.5XT 4EAT
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38 Posts
Discussion Starter #18
^^Thanks that link helped a lot.
 

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2008 XT Sports
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