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 Post subject: 6mt differences
PostPosted: Mon Apr 08, 2019 3:37 am 
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Joined: Tue Feb 20, 2018 7:01 pm
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I’ve been looking at my options for a manual swap and I’ve settled on saving for a 6mt. I’m compiling a list of parts and just wanted a little bit of clarification when it comes to transmission codes and differences. Ive seen 2 6mt swaps and both were running a trans code ty856wh3ma, from a US sti. My question is is there a difference between that trans, and a trans with the code TY856WB4KA? I’ve found a chart that gives gear ratios, and the only difference I could see was 5th and 6th, with .971 and .756 vs 1.062 and .842. Is this going to cause a problem for me or is it not a big deal. Are these 2 transmissions interchangeable? Any help would be awesome


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 Post subject: Re: 6mt differences
PostPosted: Mon Apr 08, 2019 1:41 pm 
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Those two transmissions are interchangeable. The Japanese transmissions tend to have shorter gear ratios than the us, as you posted, so their highway cruising RPMs are higher. Personally, having high cruising RPMs drives me nuts.

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 Post subject: 6mt differences
PostPosted: Mon Apr 08, 2019 2:49 pm 
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mike-tracy wrote:
Those two transmissions are interchangeable. The Japanese transmissions tend to have shorter gear ratios than the us, as you posted, so their highway cruising RPMs are higher. Personally, having high cruising RPMs drives me nuts.


Do you know about how much of a difference it makes? Currently with the auto I’m just over 3k at about 70. Is it comparable to that or drastically different? I commute about 20 miles a day, so would a us sti trans make a huge difference? I used an online rpm calculator, and it says it would be at about 3050, which doesn’t sound bad at all


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 Post subject: Re: 6mt differences
PostPosted: Mon Apr 08, 2019 3:09 pm 
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The 04/05 US one will be around 3k at 70 mph, the JDM one will be between 10 and 20% higher. That's not as bad as the JDM WRX/STI 5 speeds I'm used to

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 Post subject: Re: 6mt differences
PostPosted: Mon Apr 08, 2019 5:49 pm 
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Awesome, that actually sounds like it would be a pretty comfortable cruising rpm. My current auto cruises at about 3k give to take a few, and it often feels sluggish. 3300-3500 sounds like a nice aggressive change. Thanks for the good info!


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 Post subject: Re: 6mt differences
PostPosted: Wed Apr 10, 2019 2:54 am 
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Location: Missoula
Aside from gear ratios, there are a few different center diffs.

Some jdm cars and the spec b legacy just have a vlsd and no dccd.

04-05 is a 35:65 native torque split (this only applies with the diff fully open, when there is any dccd lockup it changes).

06+ went to 41:59, but also added an additional lsd mechanism, which uses cams to push the clutch plates together initially with a small speed difference. So it can never be fully "open." Now that I think about it, this could be the difference in the advertised torque splits. It's possible the planetary gear sets and transfer gears use the same tooth counts, and the only reason it's more forward is due to the initial lockup characteristics.

Interestingly, this cam feature was dropped from 2018, with the claim it offered better control, but it was likely for cost purposes, and possibly the inability of the diff to be fully open causes additional wear in conditions with big wheel speed differences between the front and rear (snow/ice, rally, etc).

The other thing is that later transmissions ditched the speed sensor in the transmission, I think for 2008. If you get one newer than that you will need the dccdpro vsspro or something similar. Which could be an issue getting to work on an older car, especially without abs.


But other than those differences yes they all bolt up and fit the same way.

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 Post subject: Re: 6mt differences
PostPosted: Wed Apr 17, 2019 5:06 pm 
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You could always retrofit the speedo gear into an 08+ STI 6mt. Same thing with the later 5mts. Not sure about the current non-stick 6mt's.

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