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Mythbusters: EA82 gearing...and a possible solution


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10 replies to this topic

#1 Numbchux

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Posted 15 December 2006 - 02:45 AM

So, ever since my EJ22/Rx trans swap, I've been very unhappy with the gear ratios. so over the last few days, I've done a bunch of research on gearing, and what all came with what, and what I found was rather suprising.

this is all from an '89 FSM

first off, an N/A EA82 D/R 5MT
1st: 3.545
2nd: 1.947
3rd: 1.366
4th: 0.972
5th: 0.780
Final Drive: 3.90
Lo Range reduction: 1.592

EA82 turbo FT4WD 5MT (RX or GL/-10)
1st: 3.545
2nd: 2.111
3rd: 1.448
4th: 1.088
5th: 0.871
Final Drive: 3.70
Lo Range reduction: 1.196

Myth: Because of the final drive, the turbo trans would yield lower rpms at cruise...right?

well, punch those numbers into a gear calc (like the one on Subarubrat's Website). using the stock tire height of 23", cruising at 75 mph with a turbo trans means 3500 rpms, while using an N/A trans, means 3300 rpms.

BUSTED

#2 GeneralDisorder

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Posted 15 December 2006 - 02:52 AM

Makes perfect sense - the EA82T makes more efficient power at higher RPM. And it needs all the help it can get :rolleyes:

I guess you could swap the gearset with a regular D/R.

GD

#3 Numbchux

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Posted 15 December 2006 - 03:00 AM

Makes perfect sense - the EA82T makes more efficient power at higher RPM. And it needs all the help it can get :rolleyes:

I guess you could swap the gearset with a regular D/R.

GD


haha, you beat me to it....here's my idea for a solution...


listing of common EJ gear ratios:
http://www.nasioc.co...threadid=181343

also, gen 1 legacy gearing from my '92 FSM
FWD 5MT
1: 3.545
2: 1.947
3: 1.366
4: 0.972
5: 0.738
FD: 3.70

AWD 5MT
1: 3.545
2: 1.947
3: 1.366
4: 0.972
5: 0.783
FD: 4.111


So, inspired by Beefaru's el sweeto hybrid transmission, and the fact that I had a couple RX transmissions, and a legacy 4.111 AWD trans fall into my lap (and assuming, since he's got a forester 5-speed...that other EJ gears can be used). plus the EA82 N/A D/R trans I already have (although I did promise to sell it to a buddy....). Here's what I'm going for:

EA82 N/A or AWD Legacy 1-4 (same ratios, I'm leaning towards the Legacy ones...assuming they're stronger)
FWD Legacy 5th
EA82 N/A lo range
RX center diff and final drive (the guy who's giving me the RX trannies seems to think a Mazda 323 GTX viscous locking center coupler could be used....he's got one...so I plan on finding out...).

This would give me:
1: 3.545
2: 1.947
3: 1.366
4: 0.972
5: 0.738
Final Drive: 3.70
Lo range: 1.592

which would mean, on stock tires (ignoring the fact that I'll probably be on bigger ones), this means that in 5th Hi, at 75, the engine would be turning a relaxed 2900 rpms.

And, when lo range is engaged, it would be like having a final drive of 5.9:1. Which means, in 5th Lo, 5k rpms would be 78 mph. Which would work out perfect for even the fastest of courses.

AND, still keep the locking center diff. While I have it all apart, I would really like to put in a front LSD. but that'll depend on the cashflow at the time

#4 baccaruda

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Posted 15 December 2006 - 03:08 AM

uh, do that to mine too plz :headbang:

#5 mellow65

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Posted 15 December 2006 - 03:40 AM

i figured that out a long time ago. crazy huh, better low end and better high end and better low range, what was the point of the turbo tranny. oh well

#6 bgd73

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Posted 15 December 2006 - 10:11 AM

lower compression at lower rpms is no doubt a reson for the shorter gears in the turbo. A n/a motor has thump and go from the jumpy 1st all the way through...
I have had the 3.7 to 3.9 and noticed nothing , even after paying attention to difference. Here is another calcc site for gears that can include transfer reduction:

http://www.4lo.com/calc/gearratio.htm

The 3300 at 75 is quite accurate on n/a d/r trans. I have closer to 24 inch and it rides around 3000 at 75 (very "tall" for a little engine!) at 25 inch, my particular setup is in "gear heaven" for my highway cruising. The oem engine needs a bit more air, but thats about it. :)

The swap is worth it, if you do. The turbos are so easy to get outrageous power over oem numbers.

#7 VaporTrail

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Posted 15 December 2006 - 02:05 PM

after talking with Shawn while he was digging through the trannies, I believe the biggest obstacle is the pinion gear/shaft. they are different lengths and possible milled a bit differently on the shaft as well...

#8 mikeshoup

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Posted 15 December 2006 - 02:14 PM

FYI, the Turbo pushbutton 4WD tranny has the same gearing as the N/A 5spd D/R just with a 3.7 final drive ratio.

Same goes for the Turbo pt4wd 5spd D/R, except it has a 3.7 final drive and the 1.2 low range.

Meaning the PT4WD Turbo trannies have the highest 5th gear.

#9 Numbchux

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Posted 15 December 2006 - 05:44 PM

after talking with Shawn while he was digging through the trannies, I believe the biggest obstacle is the pinion gear/shaft. they are different lengths and possible milled a bit differently on the shaft as well...


yea, I suspected that. but with this setup. I'd be using the 3.7 pinion and ring gears. along with the RX center diff....so that shouldn't be a problem....if I can get the 1.6:1 lo range gears to work, I don't see any reason to lower the final drive.


according to my FSM, all turbo 5MT models had the same gearing. whether part or full time, single or dual range. all had 3.7 final drive and 0.871 5th gear. it may have been different in other years....but it appears not in '89.

#10 mikeshoup

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Posted 16 December 2006 - 12:03 AM

according to my FSM, all turbo 5MT models had the same gearing. whether part or full time, single or dual range. all had 3.7 final drive and 0.871 5th gear. it may have been different in other years....but it appears not in '89.

It must be a year basis then. My 86 FSM says all turbo trans have the same gearing as the N/A 5s D/R. However, in 88 that's not the case as I just checked out. The S/R PT4WD trans has the same gearing as the FT4WD trans. So yeah, its a yearly thing.

#11 Numbchux

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Posted 16 December 2006 - 01:01 AM

It must be a year basis then. My 86 FSM says all turbo trans have the same gearing as the N/A 5s D/R. However, in 88 that's not the case as I just checked out. The S/R PT4WD trans has the same gearing as the FT4WD trans. So yeah, its a yearly thing.


yep, they didn't start the FT4WD 5MT until '87...so maybe that's when they adopted the different gears...




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