MT gear ratio / rpm - SWAP MT Qs??

[bearzbear]

Ok. I just put a 98 Legacy OBW on the road - after putting in a new used engine - I got it with a siezed engine. Runs nice now. But, ummmm... it turns 3400 rpm @ 75mph - a bit high.

 

After reading I see this is correct and stock! (wtf were they thinking??)

 

Anyhow, I have read that you can swap it for a 3.9:1 set up - BUT you have to also change the rear diff as well??

 

This confuses me. That means that the change in ratio is actually in the front and rear DIFFERENTiALS not in the transmission gears at all?? If the change was to the size of the 5th gears (there are two) then you could just swap the box with the gears, keep the rest.

 

So, is the change in ratio actually IN the diffs, and not the 5th gear itself??

 

Also, can I put in a newer MT with the 6th gear (I have only read about them, done no research yet)?

 

How about identifying the ratios on a REAR or the MT box itself?? How to know?

What about the rear diff off a 4EAT car???

Do I care if the parts come from the same car chassis??

 

WHICH model is most likely to have the 3.9:1 ratio parts?

What is the newest year I can use??

 

(I didn't check, but did they stop offering the MT after 2000 for a while??)

 

And, is the lower gearing mostly responsible for the better apparent gas mileage of the newer cars??

 

Any experts out there??

 

Thanks in advance!!

[johnceggleston]

Ok. I just put a 98 Legacy OBW on the road - after putting in a new used engine - I got it with a siezed engine. Runs nice now. But, ummmm... it turns 3400 rpm @ 75mph - a bit high.

 

After reading I see this is correct and stock! (wtf were they thinking??)

 

Anyhow, I have read that you can swap it for a 3.9:1 set up - BUT you have to also change the rear diff as well??

 

This confuses me. That means that the change in ratio is actually in the front and rear DIFFERENTiALS not in the transmission gears at all?? If the change was to the size of the 5th gears (there are two) then you could just swap the box with the gears, keep the rest.

 

So, is the change in ratio actually IN the diffs, and not the 5th gear itself??

 

Also, can I put in a newer MT with the 6th gear (I have only read about them, done no research yet)?

 

How about identifying the ratios on a REAR or the MT box itself?? How to know?

What about the rear diff off a 4EAT car???

Do I care if the parts come from the same car chassis??

 

WHICH model is most likely to have the 3.9:1 ratio parts?

What is the newest year I can use??

 

(I didn't check, but did they stop offering the MT after 2000 for a while??)

 

And, is the lower gearing mostly responsible for the better apparent gas mileage of the newer cars??

 

Any experts out there??

 

Thanks in advance!!

 

 

it sounds like this is your first subaru and you want some answers. well i can give you some answers but you may not like them.

 

in the late 90s, 2.2L engines came with a 3.9/5spd final drive or a 4.11/auto and they all had 14" wheels . when they introduced the 2.5L engine they changed the final drive ratios to 4.11/5spd and 4.44/auto, AND they increased the wheel size to 15" w/ a larger tire, ~2.5 inches in diameter.

 

the increase in tire size offset the change in the final drive ratio so that the difference between the 2.2L car and the 2.5 L cars was limited to the power difference in the engines. in the 90s you will not find a 2.5L car with the 3.9 final drive EXCEPT for the 96 outback manual trans. and you will not find a 2,2L car with the 4.44L final drive.

 

so you can swap the trans and the rear difff, and yes, the trans are identical, just the differential / ring and pinion are different, so you can swap the trans and the diff, but you will end up using a different part of the power curve and i do not know any one who has done it. some one certainly has, but i'm not familiar with it or how it drives.

 

the one exception to all of the above, is the 97 legacy GT, it has the 2.5L engine and the "outback" finalk drive, but it came stock with smaller, legacy size tires. this makes it "quicker" and a little more powerful and generally more fun to drive, but a little less economical.

 

it would probably be cheaper to buy some top hat "lifts" ($245) for the struts on your car and bigger tires. this would put you in a more economical setup, but i do not know how it would drive.

 

over the years, as the emmissions demands on the engines increases, the power output on these engines decreases unless they tweak the internals, which they have done over the years. so i would trust the engineers to know a little about what they are doing and delivering a car that the american public will enjoy. if you search for 'gutless' (maybe, or something similar) in posts by "grossgary" you will find some posts about his 1.8L engine in a legacy.

 

i hope this helps.

Edited August 3, 2010 by johnceggleston

[Gloyale]

you are too used to american engines.

 

3500 RPMS at 75 is perfect for that engine.

 

You wont save gas by going to a taller ratio because you wil have to open the throttle more to keep the speed.....see what I mean?

 

It's kinduv a misconception that higher RPMs = worse mileage. It all about the throttle angle.

 

Steady foot at 3500 rpms will beat stabbing the gas over and over to keep the same speed at 2500 rpms

 

Subies, like all boxer motors, like to run over and make their best power and economy between 3K and 5k rpms

[bearzbear]

Thanks for the input.

 

Ummm, no this is not my first Subaru by any measure. More like my 7th or 8th?? Going back into the 80s.

 

I do not buy the idea that the effective ratios stayed the same - I think that is true for the Automatic Transmission cars. We own a venerable '93 Legacy wagon AT, and it turns about 2700 at 75mph. More like it.

 

I know for sure that the 98 Forester (the "red pig") that just had the bolt on the timing belt tensioner come out ran under 3000rpm at 75mph, automatic transmission. Can't recall exactly what rpm it was, because it did not call attention to itself by revving out of its mind...

 

As far as a "steady foot" - I run cruise control on the high speed interstates, so it's hard to be more steady. 3500 at 75mph is too high, power at that speed isn't required much unless you have to climb very tall grades a lot. While the terrain here in upstate NY isn't dead flat like the midwest, this ain't the Rockies either...

 

This leaves running at 80mph an impractical speed for any length of time... so the car is fine for short hops, not long runs. Bums my space.

 

Swapping in older running gear seems like not a good thing. I read somewhere yesterday that the Impreza uses the same tranny but geared taller... this is the sort of thing I am looking to find.

 

Thinking about doing this swap AFTER I put in the engine, sucks quite frankly. If I had known about this loony gear ratio thing, I'd have looked for another AT car - :-\

 

[johnceggleston]

I do not buy the idea that the effective ratios stayed the same - I think that is true for the Automatic Transmission cars. We own a venerable '93 Legacy wagon AT, and it turns about 2700 at 75mph. More like it.

 

 

well, i can't say for sure but the math seems to hold up. the difference between 4.11 and 4.44 vs. the difference between 185-70-14 and 205-70-15, but again, i'm no expert. i do know they never used a tire as large as the outback's until they started using the 2.5L engine and the 4.44 final drive. if there was a huge difference, the fuel mileage wouldn't be as close as it is between the 97 lego and the 97 outback.

 

the early 90s legos had the differnt final drive ratios. the turbos were similar to the late 90s but the non-turbos were swapped. the 5 speed had the 4.11 and the auto had the 3.9, or so i'v read here.

 

I read somewhere yesterday that the Impreza uses the same tranny but geared taller... this is the sort of thing I am looking to find.

 

Thinking about doing this swap AFTER I put in the engine, sucks quite frankly. If I had known about this loony gear ratio thing, I'd have looked for another AT car - :-\

 

this is true, the auto trans in the impreza is exactly the same as the trans in the legacy and the outback and the GT and the LSi, in the late 90s. the only difference is the final drive ratios, and maybe the TCU's shift points.

 

in late 90s subarus you only have 2 choices in a/t final drives, 4.11 or 4.44.

 

why is your engine out, head gaskets?

 

EDIT: what size tires are you running?

Edited August 4, 2010 by johnceggleston

[bearzbear]

we're talkin' MT only...

 

stock recommended tires... 15" rims, I think they are 215 x 70? iirc... would have to look.

 

Imo the MT and the auto ought to be at the same RPM at highway speeds...

 

I'm talking about the Impreza MT & diffs fitting the OBW...

 

Seems to me that this MT wants desperately to have the 3.9 ratio, not the 4.11.

 

Edited August 4, 2010 by bearzbear

[johnceggleston]

we're talkin' MT only...

 

stock recommended tires... 15" rims, I think they are 215 x 65? iirc... would have to look.

 

Imo the MT and the auto ought to be at the same RPM at highway speeds...

 

I'm talking about the Impreza MT & diffs fitting the OBW...

 

Seems to me that this MT wants desperately to have the 3.9 ratio, not the 4.11.

 

 

for the most part the info above is also true for the manual trans, the two final drive ratios being 3.9 - lego or 4.11 - outback. the difference in between these (~5.4%) is less than the auto (~8.0%) but still close and the final drive ratio may not make as much as a difference as in the manual since you can hold it in a lower gear longer before you shift.

 

the 215 tires would be about an inch larger (~1%) in circumference than the stock 205s, making you travel farther / faster than the speedo says.

 

 

have you seen this "trannychart" ??

Edited August 4, 2010 by johnceggleston

[bearzbear]

as I said, "iirc" - they are stock 205-70s...

 

I don't need to hold it in gear longer, I want to run at lower RPM at high speed.

 

Right now I can easily start off in 2nd, or shift 1-3-5 for normal driving... I suppose with a full load the other gears would help.

 

To me it doesn't matter how it is arrived at, just that it is, a lower RPM for high speed travel. 3500 at 75mph is too high, period. Taller gears for me, please!

 

I don't think it is reasonable to expect to drive this car at 85mph - which is easy to have to do if passing on an interstate... or just boogying...

 

 

 

Yes I have found the "trannychart" which is why I am asking if anyone has experience getting bits or whole drive trains from other models/years.

 

How about the newer "6 speed"?? any hope there??

 

_

[wtdash]

Hi,

This Gear Ratio Calculator may be useful, too.

 

Since I may be looking for a replacement 5-speed for my '98 Forester in the future I've also noticed the 5th gear ratios for other '96-99 Subarus w/the 4.11 FD ratio.

 

On that tranny chart, the OB has the taller 5th gear - 0.871. The GT, Forester, and Impreza RS both have the lower RPM 5th gear - 0.780, if I'm reading it right.

 

I'm surprised since the Forester uses the same height of tires - ~26" - as the Outback (Forester L: 205/70R-15 and Forester S: 215/60R-16).

 

Regarding the 6-speed, I'd look thru NASIOC's threads, as it's a common upgrade for the WRX guys. Plus I think there are some 'gotchas' to watch out for w/the speed sensor changes, etc, on the newer trans.

 

Td

Edited August 4, 2010 by wtdash

[Gloyale]

Thanks for the input.

 

As far as a "steady foot" - I run cruise control on the high speed interstates, so it's hard to be more steady.

 

Cruise control actually varies the throttle quite a bit. Sure, on flat ground it's fairly steady.

 

But on rolling hills, it ussually either stabs the gas or lets off entirely to try to keep an exact speed.

 

it would actually be more effiecint to hold a dead steady throttle, and let the speed vary as you go up and down hills.

 

That said........perhaps larger tires would help you after all. Of course your speedo wouldn't say you where going faster.....so you'd have to just learn that 67 on the dash means 75 in real speed.

 

 

oh.......almost forgot.......why are you driving long distances at 80 MPH in New York? J/K

[Gloyale]

Hi,

 

On that tranny chart, the OB has the taller 5th gear - 0.871. The GT, Forester, and Impreza RS both have the lower RPM 5th gear - 0.780, if I'm reading it right.

 

 

BAckwards.

 

.780 is taller than .871

 

so it appears that the outbacks do have a lower 5th gear.

[bearzbear]

Ummm... well the traffic moves at 75mph on the NYS Thruway and the Mass Pike... you figure it out??

 

I'm not driving in NYC at that speed, ALTHOUGH back in around 1972 in my father's 64 Pontiac with the small block 8, can't recall the model, a two door - the one with the flat tops on the fenders... I had the speedo at 100mph on the Van Wyck Expressway at around 2:30AM in the morning for a short stretch...

 

As far as the cruise control dorking the gas pedal, it's more steady than your average driver, and I don't use it when going up grades - I call down to the engine room and tell them to take it out of WARP DRIVE and drop it to impulse control... but on long drives, like most of the way out to Boston it is reasonably flat and the cruise is great - just press down to pass, and then relax... try it sometime??

 

So, I am still looking for solid info on swapping in the 3.9 ratio gear... I am guessing that if I use the tranny chart I should be able to look for gear from the appropriate year/model(s) and find the codes?? to confirm the ratio. It would be tough to measure the ratio accurately enough to do an empirical determination if the rear and the tranny/diff assembly were correct.

 

And, did we decide that it is ok to use the tranny/rear from the Impreza series?? That seems like the most likely source to me... they didn't make a lot of the "premium" series OBs.

 

_-_-bear

[johnceggleston]

in auto trans in the late 90s the 7th character is the final drive ratio indicator, if it is a 2 then it is a 4.44 final drive.

 

but the manual trans are not that consistent, and i can not find any pattern to them. so you are going to have to go off of which car the trans / diff came from. a 2,5L car will have the 4.44 final drive and the 2,2L cars will have the 3.9 final drive.

 

you can check this against the chart for confirmation.

[bearzbear]

in auto trans in the late 90s the 7th character is the final drive ratio indicator, if it is a 2 then it is a 4.44 final drive.

 

but the manual trans are not that consistent, and i can not find any pattern to them. so you are going to have to go off of which car the trans / diff came from. a 2,5L car will have the 4.44 final drive and the 2,2L cars will have the 3.9 final drive.

 

you can check this against the chart for confirmation.

 

 

Yah... this is not good... because factories are notorious for stuffing in whatever parts they happen to have in stock to meet production numbers!!

 

The chart says that there are some OB and OBW that used the 3.9 ratio... but I think that sticking to the 2.2L cars as a source is more likely to yield the right part.

 

So, the numbers in the tranny chart for the MTs will not help when looking at the actual transmissions??

 

_-_-bearzbear

[Gloyale]

95-99 Impreza with either engine 2.2 or 1.8 should be 3.9 final drive.

 

though the 1.8 cars have a slightly lower 5th gear so you probably want one from a 2.2 liter for tallest possible gearing.

Edited August 5, 2010 by Gloyale

[johnceggleston]

Yah... this is not good... because factories are notorious for stuffing in whatever parts they happen to have in stock to meet production numbers!!

 

The chart says that there are some OB and OBW that used the 3.9 ratio... but I think that sticking to the 2.2L cars as a source is more likely to yield the right part.

 

So, the numbers in the tranny chart for the MTs will not help when looking at the actual transmissions??

 

_-_-bearzbear

 

the trans code numbers in the chart are / should be accurate, but when you are searching online for a trans everyone is going to identify it by year and model, not trans number.

 

http://www.car-part,com may help.

 

the only outbacks in the 90s that had a 3.9 were the 95s which still had the 2.2L engine. i do not know what happened in '00 , that's not my decade. but the rule of thumb for 5 speed swaps is "any 5 speed will fit and work as long as it has the right final drive". since you are looking to change your FD i would not limit your search to 95 - 99. review the chart and find the gears you want and then go looking for the car and year you need. i wouldn't go newer than 04 without more research just to be sure it will work.

 

there are some push and some pull clutches, but the housings have the ability to be either with very little effort, so find what you are looking for.