Tech question concerning the CVT trans and lower RPM

[Petersubaru]

I recently drove the 2010 OB and @ 60mph the RPM is 1700..while on my '01 OB the same speed reg. 2500rpm..how is it that the rpm can be dropped by 800 and not have the motor "lug"..also I have heard that the fuel consumption has improved ..and if so...is it because of the transmission or the lowering of the rpm..

[Fairtax4me]

Possibly because 1700 rpm is not low enough to make the motor lug. All of the new Legacies have the new 3.0 V6 from what I understand, which is a larger motor than the 2.5 which you probably have in your 01. Bigger motor is less likely to lug at lower RPM. It can also be accomplished with engine tuning, changes in cam height and duration, piston stroke length, bore size, lots of things.

 

Also because it's an automatic, the torque converter is able to lock or unlock, depending on conditions, to help keep the engine speed within its useful power band. When you're cruising along at a steady speed, you won't notice as much if the motor IS lugging because you're not trying to accelerate. If you want to go faster, the PCM reads the change in throttle position and determines based on engine speed, wheel speed, and throttle change if it needs to unlock the torque converter, or even downshift to allow the vehicle to accelerate easier, without lugging.

[Quidam]

Hi,

 

The CVT transmission may have a lower numeracially drive gear. I.E. 3.70 compared to 4.44, something like that. I don't know about the new CVT Subie trans tho.

 

Doug

[Petersubaru]

Possibly because 1700 rpm is not low enough to make the motor lug. All of the new Legacies have the new 3.0 V6 from what I understand, which is a larger motor than the 2.5 which you probably have in your 01. Bigger motor is less likely to lug at lower RPM. It can also be accomplished with engine tuning, changes in cam height and duration, piston stroke length, bore size, lots of things.

 

Also because it's an automatic, the torque converter is able to lock or unlock, depending on conditions, to help keep the engine speed within its useful power band. When you're cruising along at a steady speed, you won't notice as much if the motor IS lugging because you're not trying to accelerate. If you want to go faster, the PCM reads the change in throttle position and determines based on engine speed, wheel speed, and throttle change if it needs to unlock the torque converter, or even downshift to allow the vehicle to accelerate easier, without lugging.

Sorry, that I did not clarify, both cars for comparison are the 2.5L and automatic...also leads me to wonder if subaru could have dropped the rpm some years ago for better fuel comsumption and simply chose not too ??

[hankosolder2]

The thing to consider is that with a CVT, the engine can be set up to be on the verge of lugging at cruising speeds and it can "downshift" (slightly and imperceptibly) at the slightest request for acceleration. If a conventional 4-5 speed auto paired to a 4 cyl engine in a heavy car was setup to run at 1700rpm at that speed, a noticeable downshift would be required for even the gentlest acceleration or to hold speed on a gentle upgrade- with a big jump in RPM which would be annoying to the driver. Most autos are setup so they can cruise in top gear and do moderate acceleration without a downshift to avoid this annoyance.

[Petersubaru]

The thing to consider is that with a CVT, the engine can be set up to be on the verge of lugging at cruising speeds and it can "downshift" (slightly and imperceptibly) at the slightest request for acceleration. If a conventional 4-5 speed auto paired to a 4 cyl engine in a heavy car was setup to run at 1700rpm at that speed, a noticeable downshift would be required for even the gentlest acceleration or to hold speed on a gentle upgrade- with a big jump in RPM which would be annoying to the driver. Most autos are setup so they can cruise in top gear and do moderate acceleration without a downshift to avoid this annoyance.

I understand better now and why the CVT would be better choice if more mpg was important to you...the last 9 days I had an opportunity to drive a 2.4L camry..it too had a reduced rpm (2000rpm @60mph) with a regular auto tranny..the fuel consumption was better then my OB, (but not by much), but highway driving was a constant shift between low and high rpm's every time you hit the slightest hill..annoying to say the least..yes, a little better fuel consumption, but I think it is also taking a step backwards

[Quidam]

Hey Peter,

 

Here's some numbers from an AU Liberty.

 

TransmissionManual Automatic

Gear ratio - 1st 3.454 3.525

 

Gear ratio - 2nd 1.947 CV

 

Gear ratio - 3rd 1.296 CV

 

Gear ratio - 4th 0.972 CV

 

Gear ratio - 5th 0.825 CV

 

Gear ratio - 6th 0.695 0.558

 

 

Gear ratio - reverse 3.636 2.358

 

 

Final reduction gear ratio 4.111 3.7

 

LineartronicTM CVT -

 

I've driven a Subaru ECVT many miles and found I really like them. Linear, no shifting gears, it's instant. So I can see how it could rev that rpm on the highway. Linear.

 

Doug

[bheinen74]

75mph in a 92 SVX (4100 pounds) is about 2000rpm

 

80 is about 2100 rpm

i gets 26mpg in it.

 

I would hope a 4 cyl with CVT does get 32mpg like people are saying.

[Durania]

Possibly because 1700 rpm is not low enough to make the motor lug. All of the new Legacies have the new 3.0 V6 from what I understand, which is a larger motor than the 2.5 which you probably have in your 01. Bigger motor is less likely to lug at lower RPM. It can also be accomplished with engine tuning, changes in cam height and duration, piston stroke length, bore size, lots of things.

 

 

The 2.5 is still available in the Legacy and its not a V6, its a horizontal 6.

 

http://www.subaru.com/vehicles/legacy/index.html

Edited September 28, 2009 by Durania

[Quidam]

This from Subaru today:

 

Increased Durability

 

"Subaru vehicles are known for being rough and tumble, and being able to withstand years of tough conditions."

 

I'm thinking the old GL DL type stuff is what got them that reputation, certainly not the 2.5.

 

"We earned that reputation beginning with the way we build our engines."

 

They are earning their reputation by the way they build the 2.5.

 

"The flat design of the SUBARU BOXER® engine is inherently rigid, and we build each with great attention to strength and toughness. Also, power is produced with less vibration than other designs. An engine that is subjected to less vibration lasts longer."

 

I'd like someone to explain to me how a 2.5 with open deck could be stronger than a 2.5 with closed deck. Any "vibrations" would be better handled with a closed deck.

 

"It's no wonder 94% of Subaru vehicles we've built in the last 10 years are still on the road today1."

 

Yea, try counting the ones that have had "work". I doubt if Subaru would be so proud of "That" figure.

 

I know. Ouch.

 

But Sincerely,

 

Doug

 

Edit: This needs moved to:"what up with these engines?" thread. Thanks

Edited September 28, 2009 by Quidam
Post to wrong thread.

[Fairtax4me]

The 2.5 is still available in the Legacy and its not a V6, its a horizontal 6.

 

http://www.subaru.com/vehicles/legacy/index.html

 

I didn't even notice that I typed V6. I thought I read somewhere all the new ones had the 6 banger. Must have been a typo or something.

[gbianchi]

75mph in a 92 SVX (4100 pounds) is about 2000rpm

 

80 is about 2100 rpm

i gets 26mpg in it.

 

I would hope a 4 cyl with CVT does get 32mpg like people are saying.

 

???? as a new owner of an SVX 92 I am puzzeled by those numbers, reading up on it it seems they are 3600lbs and mine turns 2100rpm at 62mph, yes my TC is locking correctly, no offense intended, happy driving!!.................G

[EVOthis]

The 2.5 is still available in the Legacy and its not a V6, its a horizontal 6.

 

http://www.subaru.com/vehicles/legacy/index.html

 

+ its a 3.6 not a 3.0 ...I'm glad someone else caught part of what he said.. EZ30 has been discontinued..

[Quidam]

I recently drove the 2010 OB and @ 60mph the RPM is 1700..while on my '01 OB the same speed reg. 2500rpm..how is it that the rpm can be dropped by 800 and not have the motor "lug"..also I have heard that the fuel consumption has improved ..and if so...is it because of the transmission or the lowering of the rpm..

 

Some thoughts from experience. It doesn't lug because it's programmed to go around peak torque nearly instant, so it's able to pull the lower drive gears.

 

Ds, that's DriveSport mode with the ECVT in the Justy is programmed to rev at 3000 rpm nearly instant with a press of the gas. That puts it in peak power/torque range. It's the next best thing to a dual range tranny if you haven't got one of those, IMHO.

 

Oh, Subaru doesn't recommend changing the fluid in the new CVT "unless" under severe driving conditions, something like that:eek:

 

Not sure if I made any sense at all:)

 

Doug