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Discussion Starter #1
I have an 06 WRX that I'm thinking on doing a STi drivetrain swap but what I need help on is what year STi drivetrain has the best final drive?? Cuz I was told that the final drive varied over the years in the STi's so I want to see which one would be best for what I want to do...can anyone give me more info on this so I know what to shoot for...thanks
 

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What is it that you want to do?


Wikipedia:

Six Speed
Impreza WRX STi and Legacy spec. B

There are three six speed manual transmissions currently available for USDM Subarus. The STi and Legacy Spec B are the two vehicles that received them. The STi's 6MT has undergone various changes throughout the years, but have always had a limited slip front differential and the DCCD. In 2006, The STi's 6MT underwent some changes that included making the center differential a limited slip unit and a slight lengthening of some gears. The Spec. B's 6MT has different gear ratios (specifically 6th gear being longer) than the STi's unit, does not have DCCD, and neither the front nor center differentials are limited slip units. The Spec B's 6MT is still highly prized; however, because of its longer ratios than those found in the STi, while still retaining much of the STi unit's robustness.

Gear Ratios : 1st 3.636 2nd 2.375 3rd 1.761 4th 1.346 5th 0.971 6th 0.756 Rev 3.545 (This only applies to either the 04-05 STi or the 06+ STi, not both, and not the Spec B.).
Usage: 2004+ Subaru WRX STi and 2007+ Subaru Legacy spec. B
Early 2004 WRX STi models came with axle stubs inserted in the transmission with female front axles. Late 2004 WRX STi models came without the stubs and instead had male front axles.
The 2004 and 2005 model WRX STi 6MT was a final drive of 3.90. In 2006 and 2007 the 6MT came with a final drive of 3.545 which made the 2006 and 2007 much sought after for the non-STi WRX owners as a transmission swap. This is due to the R160 rear differential 3.545 final drive of most of the non-STi WRXs.
US Impreza WRX STi MY04 TY856WH3MA Ratios:3.636,2.375,1.761,1.346,0.971,0.756 Final Drive:3.900 DCCD:35/65 Center Diff:A.P. Suretrac Front Diff:automatic DCCD system
US Impreza WRX STi MY04 late TY856WH4MA Ratios:3.636,2.375,1.761,1.346,0.971,0.756 Final Drive:3.900 DCCD:35/65 Center Diff:A.P. Suretrac Front Diff:automatic DCCD system
US Impreza WRX STi MY05 TY856WW6MA Ratios:3.636,2.375,1.761,1.346,0.971,0.756 Final Drive:3.900 DCCD:35/65 Center Diff:Helical LSD Front Diff:automatic DCCD system
 

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Discussion Starter #3 (Edited)
Hey man thanks for the reply but quick question it said that there are 3 6mt...what's the 3??...and seeing what's said then this mean that my stock R160 rear diff is already set and all I have to do is get the 06/07 transmission??... is this correct??... and what I'm trying to do is make sure that the drivetrain I chose can take 400hp without messing up the casing and/or gears cuz that's my goal for my WRX...I heard a while ago about the Legacy trans but I wasn't told it was the Spec B all was said was the 05 Legacy wagon I should get but wasn't to sure on that persons info on what he heard...oh and I want to be able to top out at least 180mph...
 

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It looks like the 3 they are talking about are the 04-05 STi, 06+ STi, and the Legacy Spec B 6mt. The regular Legacy came with a 5 speed, not six speed manual.


Most of the guys I know that are doing LSR racing go with bigger wheels/tires to increase their top speed. But if cost is not a concern you can just have Albins build you a transmission with custom gear ratios. Theoretically my 02 WRX with JDM STi 5mt gears will top out at 170mph, but I haven't pushed it that far yet. Open air strips are few and far between.


HP is not really of concern when talking about what a drivetrain can handle. What you need to worry about is torque to the wheels. And 400hp at the crank isn't that much (it would never get you to 180mph), so honestly, if that's your goal you can just stick with the stock drivetrain.




What exactly are you building it for? If you're planning on doing events like the Texas Mile, and Maxton you're going to want to build the car differently than if you were wanting to do autocross, or even drag race.
 

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Discussion Starter #5
Well then I ain't to sure on which Legacy they were talking about then cuz they showed me a Legacy wagon from Austrailia and they said that that's the one I need to get then showed and 05 Legacy wagon from here and said the same **** so I wasn't to sure on what they was saying talking about.

So really big wheels will get you top speed. Everyone out here tells me tha if you want to go faster then I need to get like 16's or something or stay with my stock 17's but either way I'm staying 18's regaurdless what's said. See I would love to go with Albins but my pockets ain't deep to say the least. And how many HP you got if you don't mind me asking cuz if your over 300 then the casing ain't going to hold for that much longer seeing how they can hold up to 300.

I know 400hp ain't that much but its what I want to go for so I won't be able to blow my motor and loose cornering ability cuz anything after 500 your motor is at risk and more easliy able to spin out in the corners after of corse the transmission choice is situated.
I was also thinking on doing Dog Gears Straight cut after I get the trans which is more money but will be worth it in the long run of things. And really I was going to keep my trans but the one of the synchros is about to go at some point and I was looking into gear set for it but with the casing being as it is it'll break on me so that's why I'm swapping it.

Well I'm building it for autocross and some rally really and of course for street applications as well. I'm trying to do long distance races like the Cannon Ball run or the Gum Ball run here in CT so making it last is what I'm trying to do.

Oh and it my daily so I can't go over board with it now.
 

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Well I'm building it for autocross and some rally really and of course for street applications as well. I'm trying to do long distance races like the Cannon Ball run or the Gum Ball run here in CT so making it last is what I'm trying to do.

Oh and it my daily so I can't go over board with it now.
These are four diametrically opposed goals. I suggest very seriously that you buy an additional three cars.
 

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And how many HP you got if you don't mind me asking cuz if your over 300 then the casing ain't going to hold for that much longer seeing how they can hold up to 300.

Depends on how you calculate it.. using the standard 27% drivetrain loss most people assume for the WRX, that would put my car right around 550hp (although my car is dynoed on what is quite possibly the lowest reading dyno in the US, so many people would argue that number should be +30whp give or take - so that puts it somewhere between 550 and 600hp I guess?).. and no problems with the transmission yet. My car had 306whp for years(~20,000 miles), which would equate to ~390hp. That was on the stock [early]02 5mt, the weakest transmission the WRX ever came with in the United States. When I pulled the gears out to upgrade them they looked virtually brand new.



I don't anticipate any problems with the casing on my transmission in the near future. Eventually I'm going to have a new one built with helical PPG gears, new forks, and a mechanical front LSD (I already have the JDM heavy duty center diff). Even then, I'm still going to be using the 5mt casing with around 440ft/lbs of torque. I'll let you know if it doesn't hold up.. but don't expect to be hearing from me any time soon. ;)
 

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You may have a point but I'm going to make it an all round car so I'm going to see if I can make it between it all
There's little to discover. You can't build against two different rule books, and your goals involve at least two different rule books. If you pass tech at one place, you should not pass tech at the other -- and if you do, you should consider not participating because I'd have reduced faith in tech at that point.
 

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Discussion Starter #10
Wow man I didn't think those trans can hold that much for that long on stock gears. Is your 2.0 fully built? And do you use it as your daily?
 

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There's little to discover. You can't build against two different rule books, and your goals involve at least two different rule books. If you pass tech at one place, you should not pass tech at the other -- and if you do, you should consider not participating because I'd have reduced faith in tech at that point.
Well again you have a point but the way I see it as long as I know I can do those type of things even though it don't follow whatever guidlines they may have I beleave I should still be ok with others
 

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Wow man I didn't think those trans can hold that much for that long on stock gears. Is your 2.0 fully built? And do you use it as your daily?


It's not a 2.0 anymore, it's a 2.5.. and yes, it's fully built, and my daily driver. What the transmission can and cannot handle is 95% about the way it's driven and 5% how much torque the engine makes. Some people will break their transmission at stock power levels, and some people will have no problem with it at double stock power levels. Granted the more power you have the easier it will be to break the transmission, but if you drive like a sane person it should be fine. When I had 306whp and stock transmission I did beat on it a little bit.. I even launched the crap out of it one time in the parking lot when I was mad. I dumped the clutch at 6500rpm and spun the tires fully expecting my transmission to explode, but all it did was weld my clutch together a mile later down the road.
 
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