Info: Gear Ratios, Speed, RPM and Final Drive for trans swap

rmjjensen · #1 01-17-2005, 04:16 PM

I'm still trying to get my transmission stuff together for a swap. Hopefully my auto box and diff can hold up until summer time. But, I decided to calculate what the speeds and RPMs would be with various gear sets and final drive ratios from subaru transmissions. I must say I like the new 5EAT the best but I'm sure that would cost a pretty penny to install and be extremely difficult. Plus - the final drive ratio seems low.

Figured I'd share this with you guys:

#2 01-17-2005, 04:33 PM

Oh - I thought the SVX had a final drive ratio of 3.9? Everywhere I consult states 3.55 - which one is it?

Not that I am an expert or anything but from reading a lot on the boards I know it to be 3.545

Earthworm · #3 01-17-2005, 04:36 PM

Yup, 3.545

I'd still recommend the WRX 5 spd.

Our tire diameter is 24.858"

Circumference is therefore 78.09"

My gear calculations:

http://svx-iw.com/pics/gears.gif

lee · #4 01-17-2005, 05:00 PM

Quote:

Originally posted by Earthworm

Our tire diameter is 24.858"

Circumference is therefore 78.09"

I think he only counted the top (or bottom) of the tire - check by using the full value of 225 (50% on top, 50 on bottom for total height).

rmjjensen · #5 01-17-2005, 06:07 PM

Quote:

Originally posted by lee

I think he only counted the top (or bottom) of the tire - check by using the full value of 225 (50% on top, 50 on bottom for total height).

duh - I made corrections - even better yet I did the calcs for 225/40 18's and it looks a lot more respectable. I definitely like the looks of the legacy 5 speed with 4.11s

Earthworm -> Where'd that magical 0.631 6th gear come from??

3.545 definitely rings a bell .......i knew that. So this may be a stupid question - but why don't you have to swap diff gears for the WRX swap with 3.9s if it's still different from the SVX?

Earthworm · #6 01-17-2005, 06:19 PM

Quote:

Originally posted by rmjjensen
Earthworm -> Where'd that magical 0.631 6th gear come from??

3.545 definitely rings a bell .......i knew that. So this may be a stupid question - but why don't you have to swap diff gears for the WRX swap with 3.9s if it's still different from the SVX?

I made up the 0.631 gear. It's what would be required to match the 4th gear from the 4EAT (w/TC lockup). I'd love to be able to have a 6 spd with those specific gear ratios.

The WRX 5spd has a unique (to Subaru) 1.1:1 ratio AWD system. This gives you a 3.90 front diff and requiring a 3.545 rear diff.

3.545*1.1 = 3.9

mbtoloczko · #7 01-17-2005, 06:45 PM

One more correction:

SVX 4th gear: 0.694

Its listed incorrectly as 0.64 on subarusvx.com.

rmjjensen · #8 01-17-2005, 06:48 PM

Well that explains it! I love just soaking in all the information from this site. You know - I might just be able to make a custom sixth gear for the SVX. We do have a CNC machine that I can use. I'd just have to do the CAD drawing, place the material into the machine and let it rip. But - I'd need solid dimensions and to know the exact material that should be used. I might just look into it.