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2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #1
Currently has 5 speed with a ton of miles. It's my commuter car so I do at least 1000 miles a month and my primary reason for the swap is to lower my RPMs currently im at 3300 RPMs at 80 MPH and I would love to lower that, at 2900 RPMs I would save at least 1800.00 in gas per year.

Looking for an accurate parts list to do the swap but maintain the 5 x 100 wheel hubs (I have nice rims, etc.) any help would REALLY be appreciated since there seems to be a lot of options but nothing definitive on the best way for me to do this. I don't have to swap out to and R 180 but so far the consensus seems to be

04 WRX STi 6 speed
04 WRX STi R180
auto trans driveshaft
6 speed shifter
6 speed clutch and bearing etc.

But what I want is any other weird/small part/ gasket/ seal/ problem I might run into that would prevent this from being a 2 day job LOL

Anyone got specific hard info (maybe pics too) of what they did and the easiest way to get this done?

thanks so much in advance for everyone's input
 

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Premium Member
2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #2
Update I have an 05 wrx sti donor car available

Although I think that means we have to swap out a whole lot more correct?
 

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07 FXT
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828 Posts
I wanted to do this at one point, but it is a big job. If you could do it in 2 days you'd be a way better mechanic than most. At one point I mapped out the gear final drive ratios, the impact on RPM was not as great as I hoped for. My comp crashed recently so I cant get to that info, but if you came by your numbers via calculating it out then good.

I think I recall people using the driveshaft from an auto XT to make it work. I suspect the half-shafts end up being custom. If you can source a good donor car that would be great, but a wrecked 04 STI with decent running gear might be hard to find.

Also keep in mind the engine will need a different flywheel for the 6-speed, as well as the clutch you are planning for.

PS: Just saw you had an 05 donor car. If you want to keep the 100mm wheels, I think custom half-shafts would be required. I think they are not crazy to have made, just one of the many hurdles. And I see you have the auto driveshaft, I thought I read that as a manual the first time.
 

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Premium Member
2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #4

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Premium Member
2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #5
Thanks so much for the feedback and I'd love to see what the actual RPM drop is so I have a firmer Idea what difference it would make :)
 

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2004 Forester 2.5xt STI 6-Speed
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18 Posts
I think i only saw a 250-300 rpm difference after I swapped an 05 6-speed in. At most 500. Don't have the car anymore to verify 100%, but I know it wasn't more than 500rpm. That was keeping the stock forester diameter tire. There is a thread on NASIOC that lists all the final drive ratios for the different transmissions. 07 legacy spec b transmission was the lowest final drive ratio.

As for your list of part, you don't have to use the 6-speed clutch. your 5-speed clutch and flywheel are fine if you are not running a ton of power through it.
they are just smaller diameter.

Your front axles should connect to the sti trans and allow you to keep your front hubs/bolt pattern, the back is where it gets difficult. You could get the proper ratio R160 diff out of a wrx and keep your axles as they are. Then you just connect the sti trans to the R160 with the auto forester drive shaft. probably the cheapest way to do it. This is what I did.

If you are set on having the R180 axle without changing bolt pattern/hubs, then you would have to have the hybrid axles or I believe change to the 04 sti rear hubs/axles. it's been a while since i did my research, the 04 sti hubs/axles is a bit hazy.

as far as extra parts, I did my rear main seal since I was there and I needed new bolts for my exhaust because of rust. otherwise I think it was pretty straight forward.
 

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2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #7
300 RPM would be amazing frankly

That's exactly what I was figuring my calculations on, I would see at least an 1800.00 per year savings on gas based on that :)))))
 

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2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #8
would you mind PMing me your cell so we can chat for a few before I start this week?
 

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2018 Forester 2.5I Prem CVT
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I don't think you'll save as much gas as you expect. The vast majority of your MPGs at those speeds are going to aerodynamic drag. You'd only be reducing pumping losses doing this. I merely guessing here but if you did better than a 2% increase in fuel efficiency I would be utterly amazed.
 

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10 Forester X Autotragic
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198 Posts
So, im just gonna say in short I dont think you are gonna improve MPG with the STI DCCD 6 speed, the extra weight of the more robust spinning parts and the added friction of the 3 LSD units fighting each other is going to sap energy. I mean there is a reason the STI always got poorer MPG no matter what over a WRX with the same turbo, tune, tires, wingless, etc...every thing with in reason outside of the trans and diff.

If you want to get better mpg just go with a lower FD 5speed, or maybe a lower FD split case 6 speed(if you can figure out how to convert it back to manual shift linkage).

The foresters typically have 4.44 FD in the 5 speed, which is big as it gets in the Subaru OEM. There are lower FDs out there like the WRX has had 3.70 and 3.90, the STI is technically a 3.90 but some years that have the 1:1.1 center have a lower Rear FD but 3.90 upfront still. However mind these cars have smaller diameter wheels so if you were to put a 3.70 in a forester it might actually act like a 3.50 due to the taller tire and drive like a absolute dog.

Also take note: not all auto drive shafts are the same especially when it comes to the carrier bearing, the factory body lifted cars(forester, outback, baja, crosstrek), it is spaced down more to keep everything in line.
 

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2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #12
Thanks for the post

I just did the swap, and it looks like it's about a 200 rpm drop although I have not yet taken it up to commute speed yet since I drive back to vegas this weekend and it's super rainy here in LA but, wow what a totally different amazing car I have now :)



So, im just gonna say in short I dont think you are gonna improve MPG with the STI DCCD 6 speed, the extra weight of the more robust spinning parts and the added friction of the 3 LSD units fighting each other is going to sap energy. I mean there is a reason the STI always got poorer MPG no matter what over a WRX with the same turbo, tune, tires, wingless, etc...every thing with in reason outside of the trans and diff.

If you want to get better mpg just go with a lower FD 5speed, or maybe a lower FD split case 6 speed(if you can figure out how to convert it back to manual shift linkage).

I preserved the correct 3.90 final drive ratio so i will keep you posted on the results of my tests

The foresters typically have 4.44 FD in the 5 speed, which is big as it gets in the Subaru OEM. There are lower FDs out there like the WRX has had 3.70 and 3.90, the STI is technically a 3.90 but some years that have the 1:1.1 center have a lower Rear FD but 3.90 upfront still. However mind these cars have smaller diameter wheels so if you were to put a 3.70 in a forester it might actually act like a 3.50 due to the taller tire and drive like a absolute dog.

Also take note: not all auto drive shafts are the same especially when it comes to the carrier bearing, the factory body lifted cars(forester, outback, baja, crosstrek), it is spaced down more to keep everything in line.
 

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Premium Member
2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #13
 

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10 Forester X Autotragic
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I just did the swap, and it looks like it's about a 200 rpm drop although I have not yet taken it up to commute speed yet since I drive back to vegas this weekend and it's super rainy here in LA but, wow what a totally different amazing car I have now :)
Nice!

That's always been the thing, you could always any suby as "quick as an STI", or "turn as good", but it will NEVER feel like the STi. That 6speed with DCCD is the defining characteristic in my opinion and it is impossible to replicate.

What are you doing for DCCD control? DCCDpro, MAPDCCD, unconnected and what ever it defaults to?
 

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Premium Member
2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #15
Anyone have any input on the best DCCD?

Havent added a DCCD yet, am looking at a few options before I buy and install the right thing, anyone had any experiences to share with adding the "right" one?

Currently it runs on the default setting, 65 rear 35 front

Right now looking at a DCCD Pro.... But I see they have 3 different versions, so I'm not sure which one would be best for me.

There's a Manual, just has a rotary knob

there's a Spiider, it looks like that does things automatically

there's a universal, that says its for motorsports,

so am I reading the Spiider is the best one for me?

Best,

04 Fozzie STI
07 Noble M400
2001 Aprilia Mille R
2003 Big Bear Chopper Drag Bike
 

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2004 XT JDM bits
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487 Posts
I think i only saw a 250-300 rpm difference after I swapped an 05 6-speed in. At most 500. Don't have the car anymore to verify 100%, but I know it wasn't more than 500rpm. That was keeping the stock forester diameter tire. There is a thread on NASIOC that lists all the final drive ratios for the different transmissions. 07 legacy spec b transmission was the lowest final drive ratio.

As for your list of part, you don't have to use the 6-speed clutch. your 5-speed clutch and flywheel are fine if you are not running a ton of power through it.
they are just smaller diameter.

Your front axles should connect to the sti trans and allow you to keep your front hubs/bolt pattern, the back is where it gets difficult. You could get the proper ratio R160 diff out of a wrx and keep your axles as they are. Then you just connect the sti trans to the R160 with the auto forester drive shaft. probably the cheapest way to do it. This is what I did.

If you are set on having the R180 axle without changing bolt pattern/hubs, then you would have to have the hybrid axles or I believe change to the 04 sti rear hubs/axles. it's been a while since i did my research, the 04 sti hubs/axles is a bit hazy.

as far as extra parts, I did my rear main seal since I was there and I needed new bolts for my exhaust because of rust. otherwise I think it was pretty straight forward.
Put it this way...at 70mph in 6th gear I'm crusing at roughly 2700-2900 RPM.

Check to see if the 04 sti trans has the stubs or not then that will determine what axles you'll use.

Here's my 6spd conversion I did summer of 2017 and its been running flawlessly.

- Forester STI 6spd

- Forester STI (same as 05+ stubless) axles front and rear

- R180 3.9 Rear Diff (you'll have to swap the pinion flange otherwise the bolt holes won't align properly with the drive shaft) I already had an R180 installed with my WRX 3.9 5spd that was put in by the previous owner. So I'm pretty sure he swapped the pinion flange as it was an 04 STI R180. I installed my JDM Forester R180 and didn't have to swap the pinion flange as it mated up perfectly to my driveshaft flange where it mates up. When in doubt, line up the pinion flange of the driveshaft to the rear diff to ensure everything is perfectly mated. People have not swapped pinion flanges on the rear diff and were ghetto and elongated the holes to make it work. I'm not the kind to be that shady when it comes to my daily driver.

- FORESTER SG ONLY AT driveshaft **the center carrier bearing mount sits at a different position than the forester SG models. Not using a forester at drive shaft will cause a knocking noise in 1st and I believe 2nd gear due to the drive shaft angle being incorrect. I was accidently sent the impreza driveshaft and experienced this. Getting a FORESTER driveshaft cured this issue. I might have pictures if you want to see the differences**

- 04 STI+ Axles

- 5spd transmission crossmember. I was sent one in my kit but it didn't align everything properly. I cross referenced the JDM parts and it's the same as the 5spd.

- Re-use your 5spd reverse light and speed sensors. You can unbolt them from the 5spd and swap them right into the 6spd WITH the harness(es) from your 5spd.

- STI rear hubs if you plan to use the STI rear axles (if you have brembos then this is what you need anyways.)

That's as much as what I can remember what I encountered.


Here's some top tips (HIGHLY encouraged)

- You'll need a 6spd transmission clutch inspection plate. If you want to be ghetto you MIGHT be able to get away with the 5spd one but you'll have to bend the crap out of it. If you don't, then the flywheel teeth WILL touch the 5spd inspection plate!

- Replace the 6spd's oil seals IF the 6spd doesn't have stubs protruding from the transfer case.

- Replace the R180's axle oil seals as well

- Replace the Rear diff cover's gasket (I did since I opened it to perform a visual inspection.)

- Drop the 6spd's oil drain pan to inspect/clean the magnet that collects metal shavings.

- If you replace the drain plug on the 6spd BE SURE TO USE A 6 POINT SOCKET. The plug is super soft and WILL round off when using a 12point wrench/socket. Ask me how I know LOL

- REPLACE the plastic bushings around the shifter's U-Joint. It is a drastic NIGHT & DAY difference between worn out plastic bushings and brand new ones. I believe Turn In Concept sells them and I think that's where I got them or from Flat Iron Tuning. You don't want to be doing that when the trans is installed otherwise it is a PITA but not impossible.

- Replace the 6spd's tail Output Shaft's oil seal.

Basically replace any seals while you have the opportunity and not installed, it's just way easier that way.

- Ensure you follow the FSM and correctly verify/adjust the rear lockout linkage. If you do not, then you will have issues either getting into reverse or not being able to get into 5th gear. ASK ME HOW I KNOW LOL.

I hope to baby jesus in his golden fleece diaper that you don't have an issue with the DCCD center diff. THEY ARE EXPENSIVE BRAND NEW when you have DCCD. My JDM Foz 6spd had a binding center diff and once the car was warmed up, driving in a court or left/right turns from a stop, it was binding and felt like a 4wd locked up jeep diff if you know what I mean. Thankfully the JDM Foz 6spd uses the SAME center diff as the legacy gt spec b's 6spd so I replaced that rather easily.


Side note, verify the transmission code to see if it is 3.9 or 3.54. I forget what the 06-07's use as their center diff. If you don't match the transmission's center diff ratio with the rear diff (3.9 trans/3.9rear diff -- 3.54trans/3.54 rear diff) you will explode your diff and maybe experience other stuff destroyed.

I think that is all that I can remember at this point. Feel free to ask any questions. It's a pretty easy swap to be honest, but it just takes time and you being patient. While the rear diff is out, you may as well replace the rear diff mounting bushings on the rear crossmember and any other bushings along the way in that area if you have the funds since everything will be torn apart at that time. Better to spend a few bucks if you can then to remove it all later just to get it done.

All of this info, I've performed and installed at 119k ish in the summer of 2017, and I'm now at 138k as of today and she's running very well with zero issues once I sorted all the little niggling issues I encountered.:grin2:

Damn this was a long *** post lol.

??????? ????????? Subaru Forester

Use the link above to cross-reference any JDM to USDM part numbers should you use a JDM 6spd. It's been 100% beneficial to me in my previous JDM Imprezas and the JDM Foz 6spd conversion I did to ensure I could buy replacement parts/confirm various parts needed that could be acquired state side.
 

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Premium Member
2004 Subaru Forester STI Widebody, Cobb Everything, Full Suspension, Big Turbo, Brembo Brakes, Full Exhaust, Cobb V2, 6 spd
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87 Posts
Discussion Starter #17
Wow TY so much for all the great info!

So far all is good and everything is running great with the trans and drivetrain, as well as the DCCD Pro i installed :)

Best,

04 Fozzie STI
07 Noble M400
2001 Aprilia Mille R
2003 Big Bear Chopper Drag Bike
 
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