Go Back   EcoModder Forum > EcoModding > Hypermiling / EcoDriver's Ed
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 11-05-2013, 04:16 AM   #1 (permalink)
EcoModding Lurker
 
Join Date: Oct 2013
Location: Sweden
Posts: 19

Felicia - '99 Skoda Felicia LXi, MPI Hatchback
90 day: 38.69 mpg (US)
Thanks: 0
Thanked 1 Time in 1 Post
How to slow down?

I often find myself in the situation where my engine does 3000rpm, and I want to shift up to reach the sweet spot at around 2300-2700rpms.

But I also want to drive slower, to decrease aerodynamic drag!

How to drive slower, in a efficient way?
Should I just drive at 2300-2700 in third gear, and stick to the speed that gets me?

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 11-05-2013, 04:46 AM   #2 (permalink)
In the fasting lane
 
RedDevil's Avatar
 
Join Date: Dec 2012
Location: Nieuwegein, the Netherlands
Posts: 3,710

Red Devil - '11 Honda Insight Elegance
Team Honda
90 day: 51.36 mpg (US)

It - '09 Hyundai I10 Active Cool
Team Hyundai
90 day: 27.9 mpg (US)
Thanks: 1,487
Thanked 2,034 Times in 1,307 Posts
In a manual?
Never mind the sweet spot, select the highest gear you can and drive as slow as you dare.
The sweet spot is important under high load. Under light load more RPM just means more engine drag.

My 1.3 liter Insight has a CVT, but it runs at just 1800 RPM at 90 km/h and 60-70% engine load.
Would it rev to 3000 RPM to do the same then it would have about 40% engine load and lose al lot of power to pumping losses and friction. No doubt the same is true for manuals.

Buy an UltraGauge or ScanGauge so you can see the instant fuel consumption while maintaining a steady speed. No doubt you will see it improve with the higher gears.
__________________
2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.16 Gmeter or 0.1 Mmile.



Most people are in the longest queue.
  Reply With Quote
The Following 2 Users Say Thank You to RedDevil For This Useful Post:
MetroMPG (11-05-2013), PaleMelanesian (11-05-2013)
Old 11-05-2013, 10:55 AM   #3 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 21,474

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.8 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)
Thanks: 3,240
Thanked 6,090 Times in 3,156 Posts
Highest gear, lowest reasonable road speed.

People often mistake the "sweet spot" on the BSFC (Brake Specific Fuel Consumption) map as meaning that's where they should always try to operate the engine.

Not so. As RedDevil explains, that's where you want to operate the engine when moderate/heavy load is required (ie. when accelerating or climbing a steep grade).

But not when cruising at light load. Go for the highest gear/lowest RPM.
__________________
Latest mods: 3-cylinder Mitsubishi Mirage. EcoMods now in progress...
Ecodriving test:
Manual vs. automatic transmission MPG showdown



EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
  Reply With Quote
Old 11-05-2013, 02:33 PM   #4 (permalink)
EcoModding Lurker
 
Join Date: Oct 2013
Location: Sweden
Posts: 19

Felicia - '99 Skoda Felicia LXi, MPI Hatchback
90 day: 38.69 mpg (US)
Thanks: 0
Thanked 1 Time in 1 Post
Thanks guys for clarifying this for me.
Indeed I have mistaken the "sweet spot" on the BSFC.
I'll adjust my driving accordingly.

But it's better to accelerate to say.. 70km/h, and then do a EOC down to 40km/h and repeat.
Rather than cruising with low RPM on a high gear constantly on 50-60km/h?

I have some places in my regular commute where EOC is bothersome though, I'll let the engine hum along nicely at those parts then.
  Reply With Quote
Old 11-05-2013, 04:17 PM   #5 (permalink)
Master EcoModder
 
euromodder's Avatar
 
Join Date: Jul 2010
Location: Belgium
Posts: 4,666

GasDwarf - '13 Volkswagen up! EcoFuel CNG
Thanks: 176
Thanked 639 Times in 506 Posts
Quote:
Originally Posted by krrcan View Post
But it's better to accelerate to say.. 70km/h, and then do a EOC down to 40km/h and repeat.
Rather than cruising with low RPM on a high gear constantly on 50-60km/h?
You're describing the Pulse (accelerate) and glide (EOC) technique.
Surprisingly, P&G burns less fuel than running at a constant speed.

The benefit is reduced when the car is already quite efficient @ constant cruising speeds though - think direct injection diesels.

Quote:
I have some places in my regular commute where EOC is bothersome though, I'll let the engine hum along nicely at those parts then.
P&G is a hassle ...
Not all cars take it easily - some don't like being bump started, steering can get very heavy, the ignition key system might be weak ... my Volvo had all 3 issues.

Keeping the engine running reduces the effectiveness of the technique - but you might still see a positive effect.
__________________
GasDwarf's fuel consumption :
  Reply With Quote
Old 11-05-2013, 04:27 PM   #6 (permalink)
Master EcoModder
 
euromodder's Avatar
 
Join Date: Jul 2010
Location: Belgium
Posts: 4,666

GasDwarf - '13 Volkswagen up! EcoFuel CNG
Thanks: 176
Thanked 639 Times in 506 Posts
Quote:
Originally Posted by krrcan View Post
How to drive slower, in a efficient way?
Should I just drive at 2300-2700 in third gear, and stick to the speed that gets me?
The idea is that you use the sweet rpm range while accelerating, and in top gear, if possible (that is : if it doesn't mean you'd be going too fast).


You may have noticed that it's possible to get more or less the same fuel consumption at different speeds, despite being in the same gear ?

You might get a nice fuel consumption at a lower speed, and lower rpm than the sweet spot - then get the same fuel consumption at a higher speed but with rpm in the sweet spot.

That's when the better BSFC offsets the extra drag due to higher speed.


With the up! , I need to be around 2500 rpm on the motorway - that's around 85 - 90 kph.
Going slower doesn't mean the fuel consumption drops along with the speed.
FC might actually go up.

If I can follow a truck, I can go slower and have better fuel consumption as there is less drag to overcome, even at the distance that I follow.

As it's colder now, strangely enough I can't go as slow as I used to be able to in summer (warmer = lower density air = less drag).
__________________
GasDwarf's fuel consumption :

Last edited by euromodder; 11-05-2013 at 04:37 PM..
  Reply With Quote
Old 11-05-2013, 05:06 PM   #7 (permalink)
Master EcoModder
 
Join Date: Jan 2011
Location: Iowa
Posts: 1,124

Impala FFV - '10 Chevy Impala LT
90 day: 29.41 mpg (US)

XFE Coupe - '09 Chevy Cobalt XFE
Team Chevy
90 day: 38.35 mpg (US)

Penny's Rogue - '15 Nissan Rogue SL AWD
90 day: 26.9 mpg (US)

Cam's Rogue - '11 Nissan Rogue SV AWD
90 day: 26 mpg (US)

Elantra - '17 Hyundia Elantra SE
Team Hyundai
90 day: 44.68 mpg (US)

Cruze Limited - '16 Chevy Cruze Limited LT
90 day: 30 mpg (US)
Thanks: 264
Thanked 215 Times in 182 Posts
SentraSE-R experimented with different loads with engine off P&G, and if you don't do it right, almost no savings, at 70% load during accelerating, vs just leaving it in 5th gear at the same average speed his MPG was practically the same at 55mpg(32.5 mph). At 82% load 66 mpg, and 90% load 72 mpg.

Depends a lot on the car, only way to find out is to try yourself using others experience to save some time.

http://ecomodder.com/forum/showthrea...d-19594-2.html

  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com