legacycentral bbs

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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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.

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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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

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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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.

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.

All of the STI 6MTs have the same gear ratios regardless of the market as far as I know. 06 USDM uses a 1.1:1 center diff and I'm pretty sure it requires the use of a 3.54 rear diff. The only 6MTs with different gear ratios was for the JDM Spec B Legs and European market legacies with the H6 I believe. The gear ratios aren't that much different however. With 5th & 6th in the STi 6mt being 1.062 & .842. The Leggy 6mt is .971 & .756. I don't think cruising RPMs would be that much higher. I do like the idea of 5th being an underdrive rather than direct or an overdrive in the STi trans. Another thing to note is the leggy 6mt has an open front diff. I helped my friend swap his 6 speed into his 93 SS. We used an 07 Spec B trans and the only issue we ran into was not having a place to hook up speedo cable. I am doing a 6 speed swap very shorty (transmission is on order!!) and I have elected a 02 Jdm sti 6mt non-DCCD tranny for my swap. I plan on doing a detailed thread on my 6 speed swap as I have done one now and I feel I have a fairly good understanding of the process and everything required.

You can see the ratios of the US and Japanese ratios here:

https://www.rallispec.com/downloads/Tra ... Public.pdf

The ratios were tweaked by Subaru a couple times.

Oof roger, my bad. You are correct. The link you posted is broken, or atleast it's not working for me. I was able to find the information elsewhere though.
Doesn't really seem like you can go wrong with any 6mt. I think I'm going to prefer the tighter ratios of the earlier JDM STi 6mt. Looks like the JDM 04-07 Forester 6mt had an even higher overdrives for 5th and 6th yet, if one was concerned about cruising rpms. No idea if it utilizes a speed sensor though, I'm sure someone else does though.

I fixed the link.