6mt forester sti swap

Found a good deal on a JDM 05 forester sti trans/dif combo, which I'd been searching for due to the unique combo of front dif with the longer USDM spec b ratios/r180dif.

 

Can't seem to find much info on this particular swap, so assuming that its similar to other 6mt swaps as far as the particular legacy supporting parts go? Read through all the swap threads and have 4eat driveshaft, spec b rear axles, spec b shift linkage parts, and rear dif cradle all on order.

 

Being new to 6mts would also love to hear any DD clutch recommendations for a 400 hp/tq setup on a standard SMFW.

 

Narrowed it down to exedy stage 1 heavy duty (475 claimed crank torque) or southbend stage 3 daily which can supposedly hold significantly more but may have more driveability issues? Wondering if the higher holding power of the SB translates to overall longer life?

 

Reading endless threads and it seems like people have had issues with almost all the clutch options for this power level at some point.

I am running a stock STI flywheel with a stage one HD Exedy STI clutch in my 2007 Spec B, which is my daily driver. I personally like it a lot, as there is great pedal feel and it is super easy to modulate. The clutch is somewhat heavy feeling, so you have to decide whether that is something you find desirable (many people don't like the heavy feel).

 

A few observations after running this setup for some time:

1) The standard weight flywheel is really nice is you launch the car, but if you don't plan on launching at all, I would suggest a slightly lighter than stock flywheel.

2) Compared to a JDM STi transimission that I had on my previous 05 WRX, the long gearing is not quite as fun, but fuel economy is noticeably better

3) Compared to the JDM STi transmission, driving in parking lots is much smoother, due to the lack of front diff. If you really push the car to its limits in low traction environment (wet or snow), you will notice the front diff help out. However, I felt that the aftermarket DCCD helped even more in these situations, and I believe that the forester STi trans lacks DCCD (correct me if I am wrong).

 

If I were to do this all again, I would have swapped my Spec B trans out when I change the clutch to get the USDM 05 trans, shorter low gear ratios, slightly shorter upper gear ratios vs. the spec B and DCCD. I would expect a less smooth ride with that setup, and slightly worse fuel economy, but that is what I would due since shorter gearing tends to feel more fun. Hope that this helps!

Running an Exedy stage 1 HD in my '05 GT wagon track car, its putting out about 400 to the crank. No problems with it and I quite like it. Definitely a heavier feel from stock but not over the top. Unless you're doing 5k stoplight clutch dumps its plenty to hold the power levels your looking for.

 

If I were to do this all again, I would have swapped my Spec B trans out when I change the clutch to get the USDM 05 trans, shorter low gear ratios, slightly shorter upper gear ratios vs. the spec B and DCCD. I would expect a less smooth ride with that setup, and slightly worse fuel economy, but that is what I would due since shorter gearing tends to feel more fun. Hope that this helps!

 

 

 

I’m in the same boat. The spec b 6MT is a far superior transmission to the lgt 5MT but I’d switch to a STi unit if it ever needs to get removed.

400 WHP on my 6 speed with ACT HD SS clutch and stock STI flywheel. It's been a great combo so far. Only thing i can see in your parts list that you would need would be the 6mt transmission mount as the 5speed mount is different. I went with the Group N mount. Working great so far.

thanks for all the feedback.

yes, I failed to mention that I did already order a group n 6mt mount.

 

I live in the wild wild west so do a lot of longer distance driving at 80+mph, so that's really what I'm trying to get at with the grearing. I also have a pretty meaty powerband up top so in some ways its well suited for the longer gearing, or what appears to be a compromise with shorter ratios than the 5mt, but a considerably longer 6th.

 

Already have a comp stage 2 and LWFW on the 5mt so not scared of the pedal weight so much as getting cleaner takeoffs and less noise.

so this leads me to another question, don't have a lot of love for the LWFW that I currently have, chatter, decel noise etc.

 

Is anyone running an ACT streetlite? Seems like it might be a good compromise to not lose some of the free rev characteristics, but also not sound like my transmission is going to explode constantly.

 

Also, did folks with the Exedy clutch setup use the throwout bearing that came with it, or opt for the factory part?

The streetlite flywheel is fine for daily duty. Neighbor has it with the HD SS clutch in his 400whp (almost identical build to mine) GR STI. Revs a smidge faster than my car with the stock sti FW.

Exedy FTW!

after talking to a couple local big HP builders, they also recommended the Exedy Stg 1 HD for the around 400hp level, but said they only use the stock flywheel, so that's the way I'm going.

wanted to report back now that the swap is done. think it was a pretty straightforward 6MT swap similar to a lot of the writeups on here. Here's a couple highlights:

 

FSTI axles and DS didn't fit which wasn't surprising

No issues with fitting the LGT front/spec b rear axles

the locating dowels were in the transmission not the motor side so had to press those out

sensors had to be swapped over from the 5mt

The shift linkages were too short but the two factory arms from the spec b fixed it

the R180 rear dif that came with the transmission already had aR160 style yolk on it, so no swapping needed

 

All in all, it transformed the car. The shorter ratios keep the 440xt in the meat of its powerband and resolved the lag with the longer ratios in the 5mt. Its almost startling how fast you can wind through the gears. And the LSD's really seem to make the car handle more confidently, wet and dry. I got the chance to rip it in the snow yesterday and it was vicious, front pulls through turns in a way that gave it a tiny bit of oversteer, really fun.

 

Bottom line is this seems like a great option for folks wanting a 6MT with spec-B 5-6th ratios and factory installed locking difs.

I just recently bought a 2005 5 speed wagon that has right at a 100k miles on it. Just wonder how well the longer gearing would work with the NA engine. What kind of revs are you turning at 60 mph?

lot of work and cost for a NA wagon, probably about $4500 all told and that's me doing the labor. The biggest reason I did this swap is total power handling capacity and better utilizing my high rpm powerband, which wouldn't be an issue for a NA car. That said, it cruises right at 3k rpm at 75mph. Much mellower than stock gearing at speed.

chato I sent you a PM, but it is probably worth answering in the thread just to get the info in the same spot. I'm sure this swap is a little niche, but I wouldn't be suprised to see quite a few people want the same thing, Personally I think the front factory lsd and the .707 6th gear ratio is the best possible combination of all transmissions and one of the only reasons I never pulled the trigger on a normal spec B swap.

yeah, its the best of both worlds- long cruising gear, R180 and F/R LSD's.

You do need Spec B rear axles (Forester STI comes with STI style axles) and STI master cylinder. I used a 5EAT driveshaft and the same front axles. The transmission is a bit noisy, not sure if its the LSD or what, but my old one was fairly noisy as well so probably bushings related.

 

Definitely been one the of the best upgrades to the car I've done. Especially with a bigger turbo that spools later.

Did you by chance know the inner spline count for the axles that came with swap? I will probably try to just use a hybrid r180/160 race.

I don't. Its the same as Spec B axles.

On 6/19/2020 at 9:40 AM, chato said:

You do need Spec B rear axles (Forester STI comes with STI style axles) and STI master cylinder. I used a 5EAT driveshaft and the same front axles. The transmission is a bit noisy, not sure if its the LSD or what, but my old one was fairly noisy as well so probably bushings related.

Why wouldn’t the forester sti axles work? Asking because I’ve found a jdm swap online which includes driveshaft, rear diff, 6 speed trans, full wheel hub assembly, and the oem brembo brakes for a really good price. But if I can only use the rear diff and trans, it wouldn’t make sense. I’m fine with having to buy a new driveshaft to make this swap kit work, but would prefer to not have to buy axles as well. I’ve included a picture of said jdm swap kit. 

1 hour ago, sleepy2.5 said:

Why wouldn’t the forester sti axles work? Asking because I’ve found a jdm swap online which includes driveshaft, rear diff, 6 speed trans, full wheel hub assembly, and the oem brembo brakes for a really good price. But if I can only use the rear diff and trans, it wouldn’t make sense. I’m fine with having to buy a new driveshaft to make this swap kit work, but would prefer to not have to buy axles as well. I’ve included a picture of said jdm swap kit. 

Without knowing what year etc... that came out of, and going just on the photos, this is a guess, but is probably the answer you're looking for...

If that is from a Forester/STi then no, the axles don't work. Or at least since those hubs won't fit on an LGT (114.3mm) you need to get the axles for a Spec B, which fit the smaller LGT 5 x 100mm wheel knuckle/hub/etc.... So of the above, only the trans, diff and calipers are any good to you. Decide on whether or not it is worth the money based on that.

I believe the calipers can be adapted to a larger rotor for our cars, but converting an LGT to 5 x 114.3 is essentially impossible. Do a little googling around the site, and there are some pretty cool attempts. It HAS been done but the custom machining and welding required to end up with a knuckle that has quite a bit less metal supporting the bearing probably would cost more than this swap kit... So, nobody does it.

If the above kit is all 5 x 100mm, disregard this and get a new driveshaft, caliper adaptors and enjoy your 6MT. (Quick online check shows JDM Forester STi was 5 x 100 until 2005? Maybe best to verify before spending your money in any case...)

Edited August 23, 2023 by KZJonny

On 8/23/2023 at 1:05 PM, KZJonny said:

If the above kit is all 5 x 100mm, disregard this and get a new driveshaft, caliper adaptors and enjoy your 6MT. (Quick online check shows JDM Forester STi was 5 x 100 until 2005? Maybe best to verify before spending your money in any case...)

Thank you so much for the clarification. Fortunately, that swap kit is off of an ‘05 Forester STi with 54k miles. The listing does state that they are 5x100’s, but there’s no true way to verify that until I get my hands on it. I do have one last question tho… how much do you think a kit like that is worth? The seller is asking $6k. Seems a bit steep but still relatively reasonable given everything it has included. Do you think it’s worth the money if it truly does have 5x100’s all around? Thanks again for all the help!

I assume that is $6K USD?

Depends what you are after? If it was MY money, no. Not worth it. If you REALLY need a STi 6mt, then... it's not too bad. This will be a long(ish) answer, so bear with me.

Trailing arms are still not going to work on an LGT, so they are gonna be trash, and I am relatively willing to bet you'll need some adaptors to make those calipers fit on all corners, so there is a little more $$$ on top. If the spline size/count for those axles isn't the same as one available for the LGT, you'd still be on the hunt for axles, at least for the rear to go between the R180 size on the diff to a standard R160 'type' outer joint, Spec B axles would do the job. I couldn't find any info on this off the cuff, so maybe someone else will chime in, or you'll need to do some digging. My gut tells me Fozzy axles are not going to work because of size differences between the cars, but I have nothing to back that up.

The stock LGT brakes are fine the way they are with good pads and rotors. Unless you are doing some relatively serious track duty, you really don't need more than that. If the bling factor means enough to you, then all good. That's a legitimate reason as well, but I have a bias towards not spending too much money on gear I can't really use to it's potential. You can buy a lot of high quality pads and breake fluid for the couple grand a set of Brembos costs.

That leaves the trans and diff. The 6MT is the undisputed punching bag of Subaru transmissions, and will take more power than any other available. So, if your goals are big power and launches... hard yes. Get one.

If not, they're larger and heavier and especially from the STi's the gear ratios aren't that great. You don't end up dropping RPM in 6th on the highway, but you spend a lot more time shifting at lower speeds. If you're staying under....350?hp? and not drag racing, the normal 5MT should be fine at least for a while. They're also cheap to replace; I missed my chance to pick one up in decent condition, working in all gears for $100USD in the classifieds here. People have given them away. The Spec B 6MT has the best 6th gear ratio for highway driving, and even then it's only a couple hundo less RPM at highway speed. Hard to claw back $3K in transmission costs on fuel saved.

If your situation doesn't meet those conditions, I would take a minute and read a little into the people who have swapped in a 15+ WRX 6MT or the ~2010 LGT 6MT. Direct swap, same diff, axles, everything. Just need the trans, the cable shifter and a couple holes drilled to mate the gear selector to your tunnel. 6th gear is *really* an overdrive and if memory serves knock like 4-500RPM off at cruising speeds. The first 5 have a better spread for general use because 6th is a real highway gear. Costs will vary, but others seems to have been able to buy one of these and get all the bits needed to install for $1000-1500.

I spent a lot of time looking at the STi/Spec B 6MT swap and really figured I would do one, but eventually got to driving in one, and for all the extra shifting and expense in parts/axles, etc.... and the fact that my car is only maybe 270hp and the wheels, I'm not likely to break a 5mt/normal 6mt. I'm now looking for $1000 WRX 6MT, which should give me all the fun ratios I already have and *really* drop RPMs for highway cruising, which I do a fair bit of.... turning 3200RPM at highway speed for hours on end is a delightful exhaust tone, but burns waaaay more fuel than is really needed.

Edited August 25, 2023 by KZJonny

For as nice as it’d be to just go for another 5 speed, it just doesn’t make sense for me. I currently am making 320whp and 375wtq, with plans to make 475whp and 525wtq within the next year or so. Which means the 5MT would be pretty much useless in terms of reliability and longevity. I do a decent amount of high speed driving (cruising at around 85mph which in my 5MT puts me at around 3900rpms), so I definitely wouldn’t mind bringing those rpm’s down by about 500 or so. 
 

I’ve just accepted that the 5MT just won’t work for me in the long run and that I’m going to NEED a 6MT. I personally have never rode inside or driven a Spec B, so I cant speak to how the gear ratios feel. However, I have heard that the JDM Fozzy STi and USDM Spec B both have “the best possible gear ratios” for any subaru trans which is why I’m so attracted to this specific swap and not some other WRX STi swap. I have also heard that the gap between 4th and 5th gear in a normal WRX STi  is a bit bizzare and not quite the same distance apart (in terms of rpm’s) as the other gears. Again, can’t personally speak to the legitimacy of this issue but that’s just what i’ve heard.

As for some of the other things you mentioned… Brembos would be nice. Do i truly NEED them? Probably not, but there have definitely been a handful of close calls that I’ve experienced that makes me inclined to the idea of swapping on some bigger brakes.

In regard to the axles, I believe they will in fact work because of the fact that they are r180 axles and that kit comes with an r180 rear diff and r180 wheel hubs. I’ll have to double check the spline count tho.. Whether or not those wheel hubs fit onto my control arms is something I am unsure of.  

 

Oh yeah! You didn’t mention that! Hah!

You definitely do need that 6MT.

Brakes tho. If the hairy close call you had wasn’t because your brakes were heat soaked from use, the Brembos still wouldn’t have helped you. Stock brakes are limited by the size and compound if the tires, and can lock up much bigger tires than stock.

I’ve seen 6MT’s here and other places for $2-3K USD. A package deal with the diff is nice, and the brakes are a bonus. JDM stuff is usually lower mileage, which is a bonus. But with the unanswered question about hub and axle compatibility, that is a lot of extra money to roll the dice on.

There was someone around here not long ago selling a Spec B sedan w/ a second trans 6MT for a few grand… just sayin.

*really* not trying to be a downer, just chatting about what I see as how things are right now. Ask me if I actually needed a Holy Header… nope. No. Not really. But it is damned pretty and my turbo spools up faster than it used to, so the spend is justified to me.

On 8/25/2023 at 5:56 PM, KZJonny said:

I’ve seen 6MT’s here and other places for $2-3K USD. A package deal with the diff is nice, and the brakes are a bonus. JDM stuff is usually lower mileage, which is a bonus. But with the unanswered question about hub and axle compatibility, that is a lot of extra money to roll the dice on.

Yea, it’s a tough call for me to make cuz I’ve been on the hunt for a 6MT with Spec B gear ratios for a while now. So far, this is the only trans with reasonable mileage and the longer-ratio Spec B gearing. Like you said, the brakes are more of an added bonus so I really don’t NEED them. 

I guess I gotta ask myself if Spec B gear ratios are worth the $2k USD difference in price. 

I’ll do some more digging on wheel hub compatibility and let y’all know what I end up deciding to go with. 

On 6/19/2020 at 9:40 AM, chato said:

You do need Spec B rear axles (Forester STI comes with STI style axles)

 

On 1/19/2019 at 3:12 PM, chato said:

FSTI axles and DS didn't fit which wasn't surprising

 

From earlier on in this thread.....

I 100% agree that either the FSTI or Spec B gear ratios are going to be good for you, but I think at $6K for a kit what will need new axles and (DS - ?Diff support?) Is getting to where you're spending a bunch of money on parts that won't fit. I'm 100% sure the rear swingarms won't work, and I strongly doubt the front knuckes are the same....

 

Just saying, that for that kind of money you could get a well used 6MT and have it rebuilt with a racing/hardened gear set, which would probably put you well ahead of the game, so to speak.