Final Gear Change?

[Pilgrim 54]

Pilgrim 54 here. My '05 Outback wagon with a 5-speed manual is geared too low!!!! 70MPH is 3300RPM! That's simply too damn fast! Still I get 26-29 MPG But I know that I could do so much better if I could get the cruising engine speed down to about 2600. Already I'm using about a quart of oil every 1500miles and I'm not surprised at this consumption because of the Rs it's running. Has anyone out there got a fix? Are there trans gear choices? Rear ends would be cost prohibitive. For example what about using a 6-speed out of a STI? Is the 6th gear an overdrive? Seems hard to believe Subaru would use this low a gear in

Germany. There must be choices....

[Legacy777]

I'm not sure what the final drive ratio is on the newer legacies, but the highest that the legacies have had is 3.90. I'm at about 3000 rpm at 80 mph....give or take.

 

You won't really find a final drive less then that on most subarus (excluding the SVX).

 

My recommendation would be to see if you can get a higher ratio for just 5th gear. I'm pretty sure there are some options out there.

 

You may want to search http://forums.nasioc.com/forums or www.legacygt.com

[Pilgrim 54]

I'm not sure what the final drive ratio is on the newer legacies, but the highest that the legacies have had is 3.90. I'm at about 3000 rpm at 80 mph....give or take.

 

You won't really find a final drive less then that on most subarus (excluding the SVX).

 

My recommendation would be to see if you can get a higher ratio for just 5th gear. I'm pretty sure there are some options out there.

 

You may want to search http://forums.nasioc.com/forums or www.legacygt.com

80MPH @ 3000!!! Holy cow I'd leave that alone. Would love numbers like that. But as I say I'm turning 3300 RPM to get 70!!! That's simply too fast to expect decent mileage not to mention longevity. Certainly it seems that there must be someone out there who's addressed this problem.

[Steves72]

3300 rpm at 70 mph seems a little high for a factory delivered car. Are you certain that the tachometer is accurate?

 

Steve

[cookie]

Sometimes I think nobody test drives cars anymore.

[Steves72]

I was out on the highway in my auto trans 2000 obw. It turns 2750rpm at 70 mph according to the speedometer / tachometer.

 

Steve

[idosubaru]

those revolutions will not cause oil loss you're describing. i've got 150,000 mile motors that are "geared too low" in my oppinion as well. the old manual trans motors are similar in the XT6. you won't see oil loss on these motors at 50,000, 100,000, 150,000...etc. you should have that kind of oil loss inspected and corrected. i've heard others have similiar oil loss issues on some newer soobs.

[Top]

I had a 2000 OB w/manual that hit 3000 rpm a little over 60. Traded it a few months ago for a 2006 OB LL Bean. What a difference, 2000 rpm = 60 mph. I know what you mean about the high rpm on the manual OB.

[forester2002s]

My 2002 Forester spins at 3000 RPM at 70 mph.

I'm quite happy with that. It sounds and feels OK.

I wouldn't want the RPMs to be any lower, considering that Max. Torque on this engine is at about 4000 rpm.

[cookie]

My Forester is really spinning up at 70 mph but that is the nature of the beast. With no low range the car is right on the border of running out of power in the mud, a six speed would help. I have had rental cars in the last couple of years that turned 1500 rpm at the same speed.

The rental would not be much use in the mud however.

[SuperSubaru]

I feel your pain. My 97 OB M/T is the same. I have been looking for a way to solve this for a while... this car is capable of over 30MPG if it was just geared better.

 

If I can find a spare car for a while, or a mechanic that knows Subaru, I would like to do a diff swap with a SVX (3.54 gears) into my OB M/T (4.11 gears). I could care less about off the line acceleration... I drive 100 miles a day and need something that will cruise at 80 without screamin'. The A/T have taller gears than the M/T.

[otis]

I wouldn't want the RPMs to be any lower, considering that Max. Torque on this engine is at about 4000 rpm.

Isn't that why you downshift?

 

I also have a forester and I was thinking about getting tires with a higher aspect ratio to "gear up." I know the current tires has a smaller rolling circumference since my actual speed is a few mph off compared to the speedo.

[Juan]

My 2005 OBW ATranny spins 3100 at 70mph.

 

My problem is that the AT shifts into fourth at 30mph and dogs the engine at 1500rpm. It kills me to hear the engine lugging and have to drop it into "manual" and drag it down to third.

 

You've actually gotten 29MPG in yours? Must have been a long down-hill run.

 

Juan

[Snowman]

I have to disagree with a lot of people here, and say that I don't think that's too many RPMs for a Subaru engine to be spinning. Since the 1970's, Subaru has built its engines to be happy running in what is considered the "high" rev range by most standards. That's where they make power, and the fuel economy in at those revs doesn't suffer nearly as much as you might expect.

 

The old EA82s with the 3AT transmission were spinning 4000 rpm at 60 mph, and didn't burn oil or experience a big loss in MPG. Most of the loss in efficiency was due to the slipping of the non-lockup torque converter, not because of the gearing.

 

I've made trips of up to 500 miles in a 97 Outback with the EJ25 while running at 80-90 mph, which brings the revs up close to 4300. Even at those speeds, virtually no oil was burned, and at 90 mph, I was still getting over 20 MPG.

 

In my car, a lifted 86 wagon with an EJ22 engine from a Legacy, I've experimented with running in different gears at highway speed, since my oversize tires have increased the effective final drive ratio a great deal. If I stay in 5th gear, the car requires a lot more throttle to maintain speed up hills than if I shift down to 4th. Despite the higher RPMs, my fuel economy improves when I keep the engine in its "happy" range, which is usually between 3000 and 4000 rpm.

 

As to the oil consumption, I've seen lots of EJ-series Subarus that unexplainedly burned oil. In almost all of those cases, a new OEM PCV valve eliminated the oil usage.

[otis]

Subaru has built its engines to be happy running in what is considered the "high" rev range by most standards. That's where they make power, and the fuel economy in at those revs doesn't suffer nearly as much as you might expect.

I don't know if this as a fact- so this is just speculation on my part. but I would think that if you're driving 65 mph in 5th gear at 2000 rpm vs 65 in 4th going 4000 rpm (I'm just making up numbers here), i'd think you'd be burning TWICE the gas in 4th gear for going the same speed.

 

so take OP's original thought-- if he was driving at 70 mph at 3300 rpm then he's buring 27% more gas than if he were at 2600 rpm which could translate to an increase of 5-10 mpg (assuming linear relation to rpm and fuel consumption). I have no idea if this is right or wrong, but it makes sense intuitively to me.

[forester2002s]

...i'd think you'd be burning TWICE the gas in 4th gear for going the same speed.

 

Gas consumption includes many variables, engine speed being one of them.

 

But 'throttle position' (read 'fuel flow') is also a major one.

 

So at twice the engine speed, the 'throttle position' would be much lower. Who's to say what the resultant gas consumption would be. It's not that simple.

[idosubaru]

if he was driving at 70 mph at 3300 rpm then he's buring 27% more gas than if he were at 2600 rpm which could translate to an increase of 5-10 mpg (assuming linear relation to rpm and fuel consumption).

that's part of the equation, but there is far more involved than that.

 

i've done a lot of number crunching on these mileage figures over the years of owning various XT6's. proof is right here, all highway miles, road trip numbers, i've owned about a dozen of these i'm fairly familiar with them:

 

Subaru XT6 automatic AWD - 28.5 mpg roughly 3,000 rpms at 75

Subaru XT6 manual AWD - 27 mpg roughly 3,500-3,700 rpms at 75

 

unless you want to take the side that automatics are more efficient than manuals (which noone would do), the optimum running range for highway gas mileage for the kind of driving i do is in the 3,000 RPM range. my automatics have given me better gas mileage and that's cruising 75 - 80 mph....i may get better if i drove 65 but i'm not about to do that on a long road trip.

 

that being said - an old FWD manual EA82 non-turbo subaru can get 40 mpg. but i don't recall the RPM's those transmissions run, it's been a long time since i've owned the only FWD subaru i had. but i got 40 mpg on highway trips.

 

i'm not a fan of the higher gearing of manual trans either, but it shouldn't affect the motor at all, but it does seem better gas mileage could be had with different gearing on the manual trans.

[Snowman]

I don't know if this as a fact- so this is just speculation on my part. but I would think that if you're driving 65 mph in 5th gear at 2000 rpm vs 65 in 4th going 4000 rpm (I'm just making up numbers here), i'd think you'd be burning TWICE the gas in 4th gear for going the same speed.

 

so take OP's original thought-- if he was driving at 70 mph at 3300 rpm then he's buring 27% more gas than if he were at 2600 rpm which could translate to an increase of 5-10 mpg (assuming linear relation to rpm and fuel consumption). I have no idea if this is right or wrong, but it makes sense intuitively to me.

 

It depends on where the engine makes power. Generally, you want to run at the lowest RPM at which the engine is still making peak torque. Below that RPM, it's struggling to keep up, you have to use more throttle, and more fuel is burned. For example, an EA82 engine makes peak torque at 2800 rpm. Running at 2000-2500 RPM on the highway will probably burn MORE gas in that engine that running around 3000-3500. (That's an extreme but in my experience true example...the EA82 makes NO power below 3000, so you'd probably have it pretty close to the floor to keep it in 5th gear at 2000 RPM).

[cookie]

In the 30s cars were geared low and an overdrive came to be offered. On early Jeeps a very popular accessory was the Warn overdrive. I think they had to be in two wheel drive though. Probably the best answer is to have a six speed tranny for a Subaru.

[SuperSubaru]

First let me start off: I am a mechanical engineer, I emphasized my career in engine design, and still work in the field.

 

Peak torque and HP are for marketing and advertising. The number of times the general public ever uses these numbers is less then 1%. Gas mileage has less to do with RPM and much more to do with throttle position. Peak torque and HP numbers are attained at WOT (wide-open throttle).

 

I agree torque is more important to fuel mileage. If I build a brute of an engine with gobbs of torque, I could cruise @ 80mph @ idle. But mind you that would be a pretty big engine, and probably diesel.

 

Car makers don't design for gas mileage at real world expressway speeds (70-80MPH). They design to do the best on the EPA testing (if I remember correctly is like 50-55MPH), again for advertising purposes.

 

So look at your RPM at 55MPH, top gear. That is the engine speed your engine is tuned for (it may be your peak torque RPM, it may not... ). This is the RPM I am going to try to put my sube at, but rather at 75MPH.

[Tiny Clark]

If I geared the the rear in our 2.2 '96 so the rpm's would be lower, I'd have to shift the auto tranny into 2nd to get up a hill! Hell, it's bad enough the way it is...

[northgeorgiaroo]

I think cookie had the point, but it got overwhelmed by the engineering and number-crunching going on.

If you want a higway runner, don't buy an outback. It's not only evidently geared low, it's way too high off the ground to run at 80 comfortably.

When you design a vehicle with off-highway performace in mind, you lose higway performance. It's that simple.

I'd rather run at a little higher rpm on the interstate than stall out the first time I try a nasty hill on the way to camp.

 

A dual-range 4wd would be the ideal solution, but Subaru seems to have given up on that.

[Legacy777]

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