6mt Split Case Swap

Stevebsy · #1 11-05-2018, 06:06 PM

Time to reignite the love affair with the SVX!

I'm looking at doing a 6MT swap that I haven't seen anyone else do yet....

a 6MT but the newer Split case design used on the 2010ish cars and newer.

From what I understand, it's the old 5MT case, but with an extra gear inside, and the shifting is done via cable instead of direct linkage.

Like this one:

https://www.ebay.com/itm/Manual-Tran....c100284.m3505

I see a few positives here:
1. Less expensive than the STi duty 6MT
2. Less weight and bulk than the STi 6MT
3. Cable shifter so the linkages wouldn't have to be modified
4. Good ratios for highway cruising

Am I crazy or what?

irox · #2 11-05-2018, 06:52 PM

Awesome! I was also wondering about those! Being able to easily locate the shift seems like plus.

What RPMs are you expecting compared to stock?
I did the calcs for a bunch of transmissions, this one 4.111 with 0.695 top puts it about 600rpms over stock (for the same speed in top gear). Seems like a lot, but many transmissions are much higher... Swapping the top gear from you automatic would drop the to 400rpms over stock.

(If I've remember correctly....)

Please us know how this works out. Both from the the easy of installation, and the final drive-ability.

Cheers!
Ian.

Stevebsy · #3 11-05-2018, 08:49 PM

Someone can/should check my math:

Stock SVX Tire 225/60/16 =812 revs per mile

80 mph = 64960 revs/hour = 1082.67 rev/minute

1082.67 * 4.11 diff = 4449 rev/minute at diff
4449 * 6th gear @ .695 = 3092 RPM @ 80 MPH (Non-turbo trans)
4449 * 6th gear @ .666 = 2963 RPM @ 80 MPH (Turbo Trans)

Either of those is good with me...

The Best ratio in the HD 6MT is .707 x (3.900 /1.1) which gets 2713 RPM @ 80 MPH
which would also be fine.

I have a daily commute on 80MPH roads, so the final ratio is important for me.

irox · #4 11-06-2018, 01:41 PM

The ".707 top 3.9 diff" is what I've been looking for.
Although I would swap the 0.64 gears from the auto transmission (apparently you can do this without dismantling the entire transmission - and can even do it without removing the transmission if it's already mounted).

This should give 2392rpms at 80mph.

There was a subaru trans for their diesel engines with a 0.56 top, it's on 4.444 diff, but still delivers low RPMs compared to other offerings.

I also wonder about a custom trans, with the 3.545 diffs swapped into a 3.9 diff transmission. But not sure that would be possible without significant fabrication...

Cheers!
Ian.