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When you say 2015 6spd, do you mean from the WRX or from the STI?
 

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Isn't the diff a different ratio?
Yes.

@REPOMAN555, there are a lot of unknowns here, so I don't know what you'll need as a total parts list. You'll definitely need the transmission and rear diff from a 2015. Since the rear diff is an R160, I can imagine it will bolt up with the OEM 2004 driveshaft, but you'll want to check the length and mating splines for compatibility. The 2015 diff would also need to bolt into the rear subframe, so mounting holes would have to be identical as well.

Then there's the driveshaft and hubs -- need to confirm compatibility. The 2015 WRX uses a completely different knuckle and suspension setup and 5x114.3 hubs, so the suspension will not bolt up. And icing on the cake, the WRX 6MT uses a cable-actuated shifter assembly and a different clutch mechanism so you would need to fabricate a shifter box and new clutch pedal box.

All this is to say... there's no way it would be worth it. The amount of time and effort to make the swap seems to be astronomical in price and for what? The WRX 6MT isn't particularly strong. For the price, it seems you could have an STI 6MT AND DCCD controller plus some money in your pocket to replace all the other parts that are bound to fail in the near future.
 

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Discussion Starter · #6 ·
Yes.

@REPOMAN555, there are a lot of unknowns here, so I don't know what you'll need as a total parts list. You'll definitely need the transmission and rear diff from a 2015. Since the rear diff is an R160, I can imagine it will bolt up with the OEM 2004 driveshaft, but you'll want to check the length and mating splines for compatibility. The 2015 diff would also need to bolt into the rear subframe, so mounting holes would have to be identical as well.

Then there's the driveshaft and hubs -- need to confirm compatibility. The 2015 WRX uses a completely different knuckle and suspension setup and 5x114.3 hubs, so the suspension will not bolt up. And icing on the cake, the WRX 6MT uses a cable-actuated shifter assembly and a different clutch mechanism so you would need to fabricate a shifter box and new clutch pedal box.

All this is to say... there's no way it would be worth it. The amount of time and effort to make the swap seems to be astronomical in price and for what? The WRX 6MT isn't particularly strong. For the price, it seems you could have an STI 6MT AND DCCD controller plus some money in your pocket to replace all the other parts that are bound to fail in the near future.
Thank you
 
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