how to shift for lowest fuel consumption?

[guyc]

Hello

 

We are driving a Legacy Wagon 2.0 GL from 2002 (JF1BH5LJ4, engine # EJ201MJDAA), manual 5 speed. We are living in Belgium (Europe).

 

I was wondering what the best possible ratios are to shift gears as economical as possible. When I looked in the manual that came with the car, I found the following:

 

Gear...........Minimum.....................Maximum

..1........0 km/h........................24 km/h...2600 rpm

..2.......24 km/h...1500 rpm........40 km/h...2800 rpm

..3.......40 km/h...1900 rpm........65 km/h...3200 rpm

..4.......65 km/h...2400 rpm........73 km/h...2700 rpm

..5.......73 km/h...2000 rpm......188 km/h.........? rpm

 

Let's say: I found the speeds in the manual, and I found out the corresponding rpm (approximately) while driving!

 

But this doesn't make any sense to me, knowing that the maximum torque is reached at 3600 rpm. And I thought that the maximum torque is the point where the engine gives the most power for relatively the least fuel consumption. So I would say: shifting when the engine reaches 3600 rpm?!

 

Who can help me: when do I have to shift to drive as economical as possible? Can anyone provide torque curves including rpm and the corresponding gears that could clarify this?

 

For those who find this not interesting or ridiculous: please do not answer. Here in Europe (and I hope also in the rest of the world) driving is not only fun. Ecology becomes more and more important, certainly when you know that 95% of the cars here are manually shifted. (Our previous Legacy was an A/T, though.)

 

I look forward for your response.

 

Thanks

 

Guy, Belgium

Edited April 17, 2011 by guyc
wrong year (MY)

[MilesFox]

I find the subaru is happiest at mid-rpm. It almost makes more sense to accelerate mre quickly to your desired cruise speed, and then from there, feather the pedal to maintain.

 

I do notice, however, that i get better fuel economy cruising at 70 mph than at 60 mph, since the rpms are in the sweet spot.

 

one thing to consider is a vacuum gauge, so you can watch the laod on your pedal as you are driving.

 

I try to practice hypermile techniques such as minimal braking, and carrying momentum as much as possible, as if driving a large truck with no brakes.

[guyc]

Hello Miles Fox

 

Thx for your reply. But I'm wondering how I can compare your situation to mine.

 

- Are you driving an A/T (4- or 5-speed) or a M/T?

- Which Subaru do you drive? Which year?

- Do you often drive in a remote area? (Here in Belgium "cruising" is almost impossible, unless you drive on highways, because it is so densily inhabited)

- What do you mean by mid-rpm?

 

Another thing is comparing fuel consumption figures: in Belgium it is expressed in liter/100 km, in other countries in km/liter, miles/liter or miles/gallon! So comparing this will mean to do research in Google. And then our car runs on LPG (consuming approximately 12,5 liter/100 km), so I don't have any idea how much gasoline our car consumes (maybe some 10 liter/100 km?).

 

I would like to get more specific answers (the only thing we really can compare, are the rpm's).

 

Greetings

 

Guy

[zyewdall]

I am not sure about the newer subarus, but I've noticed that in my older ones (EA82's) I actually get just as good of mileage when shifting at 4,000 compared to shifting at 2,500 ish. Lugging an engine is bad too, and with that small an engine, a higher rpm is probably understandable (the Justy is even higher... power band really doesn't start till at least 3,000). I think alot of people who use the 2,500rpm "rule of thumb" for best gas mileage are used to old V8 engines with carburetors that have power below 2,500, and open the secondary on the carb at higher rpms and really guzzle gas there. That being said, the newer subaru engines are alot bigger than the old 1.8's, and I'm not sure if they should be run at lower rpm's or not... my truck has a 4 liter V6 engine, all new and computerized -- should have a diesel really... but those were never sold in the US -- and it definitely drops in mlieage when you keep it at higher than 2,400rpm or so.

 

Feathering the gas vs flooring it is definitely a big differentiator though, regardless of rpms.

 

Getting one of the instantaneous mileage gauges is a good way to try out different methods though. You can shift into different gears (rpm ranges) on the same grade and immediately see whether it's better to have a higher rpm in a lower gear, or downshift and slow the engine down, but have it producing more torque.

[hankosolder2]

Guy,

 

I'm not sure that answers from a primarily North American Subaru board will be relevant to you- the 2.0 engine was never sold here and likely has a different torque curve and gearing than the 2.5 liter engine sold in our '04 model year cars.

 

In general, supposedly upshifting "early" but not so early as to require the engine to lug in the next gear is the best. Why not keep close track of your fuel economy and experiment with different shift points and see what works best with your particular car and driving conditions?

 

Nathan

[Fairtax4me]

But this doesn't make any sense to me, knowing that the maximum torque is reached at 3600 rpm. And I thought that the maximum torque is the point where the engine gives the most power for relatively the least fuel consumption. So I would say: shifting when the engine reaches 3600 rpm?!

Not so. It may be the most powerful point in the engine rpm range, but it is almost never the most fuel efficient. With light throttle driving I get the best fuel economy shifting around 2,000 - 2500 rpm. Sometimes going up the hills here I don't have any choice and have to shift at a higher rpm, or the engine will not make enough power to get up the hill in the next higher gear.

[Turbone]

I learned long ago that short shifting in any car saves fuel. As long as you dont bog the engine with to low a rpm you should see a increase in mpg.

If race car drivers can do it, so can we

[rverdoold]

I get 35 mpg with my 1.6 MT impreza (AWD) on gasoline and 30 mpg for propane.

The trick is not to pass 2750 rpm when not needed. I usually shift at 2100 when not in a hurry, it then comes back at 1600 after changing. The biggest saver is leaving in gear when possible. When getting off the highway just let go of the gas and only change it back to 1st when at stand still.

Second thing I have my tires inflated to 2.8 bar (40 psi) for 185/65/14 winter tires. I just mounted my summer tires and will see if it remains the same. Same pressure but at size 205/55/15 but will change them to low resistance continental or michelin tires with size 195/65/15.

I monitor using Mycar-monitor to register all expenses and to see how much it actually cost to drive. At the moment I am at 0.16 euro cents per km all including maintenance, insurance, tax, fuel and 1000 euro depreciation per year.

 

edit:

I found the SEA paper of subaru for the new boxer engine in 1989 there is a graph (32) which shows the fuel vs rpm consumption

http://www.surrealmirage.com/subaru/files/SAE_boxer.pdf

 

(thanks to http://bbs.legacycentral.org/viewtopic.php?f=5&t=1338)

Edited March 28, 2011 by rverdoold

[Setright]

Accelerate using roughly 50% throttle, and get to the intended speed quickly. Miss a gear shift too. And then run at a constant speed as far as possible, in the highest gear that keeps you over 1500-2000rpm.

 

From standstill...1st gear until 2500-3000rpm, then 2nd all the way up to 60km/h...and straight into 4th.

 

 

Yes, it really does work.

 

 

Slow acceleration, and too much throttle feathering is old-style, for carburator engines, with acceleration pumps. Multi-point electronic injection requires new thinking and driving styles.

 

 

Also, coupled with the shorter stroke, compared to older engines, there just isn't the torque needed to pull high gear/low rpm. That's why it is wrong to only use first gear to the get the car moving, and then shift into 2nd as soon as you can. You need to accelerate enough to make 2nd pull cleanly from no less than 1500-2000rpm.

 

High rpm's, during acceleration aren't the killer of good economy. Steady speed cruising with high rpms will often be less economic. But look also the amount of throttle opening...sometimes, higher rpm, with the engine breathing optimally, with give the best economy.

 

I am NOT saying you should drive around in 2nd gear, with 5500rpms Just consider if maybe 3rd gear is the best for city traffic, where I expect your speed swings from 40-60km/h. Don't worry about 4th gear, stick with 3rd, this will also keep the rpms high enough to allow fuel cut-off when you release the throttle. And 3rd should still pull well at 40km/h.

 

 

( I am European too, and have owned and driven many manual Subarus)