Recent Topics
STP mulit purpose motor treatment + fuel stabalizer
by Chris142 - 11/14/19 08:08 AM
"Universal" electric coolant circulation pump
by Superflan - 11/14/19 07:32 AM
Thermostat question
by nicholas - 11/14/19 07:13 AM
why michelin changed their tire lineup?
by edwardh1 - 11/14/19 07:12 AM
how do you mark your name on key fob?
by edwardh1 - 11/14/19 07:08 AM
"New EV Battery Can Charge in 10 Minutes..."
by wemay - 11/14/19 05:52 AM
TDS review
by Espada - 11/14/19 03:30 AM
SD40 Guide Rod ?'s
by GumbyJarvis - 11/14/19 01:08 AM
How many steps a day are you getting?
by P10crew - 11/14/19 12:45 AM
Pics - Top Piston Cleaning - Lexus CT200h
by KerryB - 11/14/19 12:14 AM
Valvoline Full Synthetic Maxlife 10w30
by KerryB - 11/13/19 11:38 PM
Toyota 1MZ-FE burning lots of oil
by Speedinsweede - 11/13/19 11:27 PM
Castrol Magnatec
by dosmom - 11/13/19 10:51 PM
How do you feel about buying tires with different DOT's?
by Speedinsweede - 11/13/19 10:23 PM
Toys for the Caprice
by ls1mike - 11/13/19 09:08 PM
7.62x39 AR anyone?
by sw99 - 11/13/19 09:07 PM
Chrysler EcoDiesel Class Action Suit
by JeffKeryk - 11/13/19 07:45 PM
2015 Mazda 6 Auto-RX rinse Castrol EDGE 0W20
by bulwnkl - 11/13/19 07:45 PM
Where's Trav 2.0?
by user52165 - 11/13/19 07:20 PM
Newest Members
PaulDouglas, DanF350man, Jasonoff, Speedinsweede, JeffS
69856 Registered Users
Who's Online Now
84 registered members (alarmguy, 2015_PSD, Andrei, 64bawagon, 1978elcamino, 4WD, 9 invisible), 2,011 guests, and 20 spiders.
Key: Admin, Global Mod, Mod
Forum Statistics
Forums67
Topics297,391
Posts5,114,530
Members69,856
Most Online3,589
Nov 2nd, 2019
Donate to BITOG
Print Thread
Hop To
Page 1 of 2 1 2
Fuel Mileage - Quick vs. Steady Acceleration #5243421 10/18/19 01:16 PM
Joined: Sep 2019
Posts: 45
O
onespiritbrain Offline OP
OP Offline
O
Joined: Sep 2019
Posts: 45
My wife and I have very different driving styles; I drive slow and steady, often taking 20-30 seconds to reach cruising speeds, and Tiffany takes off like a rocket until cruising speeds. There was a time we were sharing a vehicle (because mine was a bucket full of buttholes) and I found that the vehicle would achieve 2-3 mpg better when I didn't drive it at all. I was perplexed and taking sharp notice of anything that could've attributed to her somehow being a better driver than me. I am biased, but I found nothing. I later decided it must be because of my slow driving style.

So, I have set out to recreate the scenario and perform a test to confirm the above but I cannot for the life of me be consistent enough to get any useful results. I used to have an incredibly easy drive where I never had to romp the skinny pedal but now I simply must, pretty much daily, unless I want to wait until traffic hour is over to pull out...

Now that I have given this more thought I realize no one is going to have a scientific answer, if anyone has an answer at all.. but I've already typed it up so here it goes.

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243442 10/18/19 01:45 PM
Joined: Aug 2019
Posts: 46
B
benjayman227 Offline
Offline
B
Joined: Aug 2019
Posts: 46
Not the first person I've heard with this experience. If that's any consolation.

When I first started learning about my cars, one of the most interesting graphs in the technical report for the 1ZZ-FE was the BSFC graph. This graph essentially shows the amount of fuel consumed per HP produced. Interestingly, it falls off moderately from idle to around 3k, then stays pretty flat to about 4k, then spikes sharply up through the redline. So that means, the engine is most efficient from 3-4k assuming a fully-loaded engine.

Now lets go through the physics. It takes some fixed quantity of energy to accelerate a car to X speed. Energy is power times time. Reducing the power increases the time (as you have demonstrated) and vice-versa. The slope of that graph is linear. So now combine the power-energy graph with the BSFC graph, and you can integrate the BSFC data at a specific HP value over the corresponding time interval to give a total fuel consumption for the acceleration. I haven't run the numbers, but my guess is THAT graph will bottom out somewhere near where the BSFC graph inflects upward (around 4k).

If I get a chance to run some actual numbers, I'll be sure to post the results. But this is the rough idea.

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243458 10/18/19 01:58 PM
Joined: Dec 2017
Posts: 2,919
J
JLTD Offline
Offline
J
Joined: Dec 2017
Posts: 2,919
Benjayman227, I must condense your scientific post down a bit:

There's a point on the curve where "more gas for less time" uses less than "less gas for more time"


I use the overseas manual to choose my viscosity.

Using AMSOIL

Hers: 2008 Jeep Liberty 154k, SS 5w30/Amsoil

His: 2015 4Runner 60k, SS 5w20/Amsoil

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243460 10/18/19 01:58 PM
Joined: Mar 2016
Posts: 1,335
C
CharlieBauer Offline
Offline
C
Joined: Mar 2016
Posts: 1,335
Looking at the difference simplistically, you're spending more time in lower gears which are way less efficient than higher gears.


It ain't what you don't know that gets you into trouble. It's what you know for sure that ain't so.

- mistakenly attributed to Mark Twain
Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: CharlieBauer] #5243510 10/18/19 02:57 PM
Joined: Feb 2003
Posts: 8,962
C
Cujet Offline
Offline
C
Joined: Feb 2003
Posts: 8,962
Originally Posted by CharlieBauer
Looking at the difference simplistically, you're spending more time in lower gears which are way less efficient than higher gears.

That's a great answer and is actually true!

Remember that the amount of energy required to accelerate a mass to a given velocity is independent of the rate of acceleration. Moderate acceleration to achieve cruise speed is good when the drive segment is longer.

Gas engines will enrich under heavy loads and hard acceleration. Something less than full throttle is probably best. Maximizing time spent at efficient speeds is generally good, unless it's city traffic. That requires a gentle technique to achieve good MPG in a gas vehicle, a technique that is infuriating to other city drivers.

In a Tesla, the rate of acceleration does not appreciatively affect range. Yes, there are some technical losses due to higher conductor resistance and slight changes in motor efficiency. But the effect is so small, a full "throttle" model S, P100D run to 60 is known to "waste" only 100 watts for the 3 seconds of acceleration, vs reaching 60mph in 20 seconds. Technically insignificant with a 100,000 watt hour battery.


People who count on their fingers should maintain a discreet silence.
Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: CharlieBauer] #5243518 10/18/19 03:06 PM
Joined: Sep 2019
Posts: 45
O
onespiritbrain Offline OP
OP Offline
O
Joined: Sep 2019
Posts: 45
Originally Posted by CharlieBauer
Looking at the difference simplistically, you're spending more time in lower gears which are way less efficient than higher gears.

Aha, yes of course. It'd be similar to the mpg loss from having gigantic tires(in addition to increased rolling resistance) or installing a higher ratio differential gear set.

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243538 10/18/19 03:31 PM
Joined: Nov 2012
Posts: 866
P
Pelican Offline
Offline
P
Joined: Nov 2012
Posts: 866
What's the other traffic doing while you "Take your time" to reach the posted speed?

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243587 10/18/19 05:02 PM
Joined: Aug 2018
Posts: 227
B
bobdoo Offline
Offline
B
Joined: Aug 2018
Posts: 227
Driving the same 40 miles one-way, for 15 years, I tested this in three cars. 2000 Outback 5-speed, 2006 audi a4 turbo automatic, 2012 Subaru Impreza w/CVT.

In every car, every season, the *slowest* acceleration made significantly better MPG. By slowest, I mean a throttle opening barely above steady-state. (I drove on two-lane country roads, so could drive as slow or fast as I wanted).

People confuse *efficiency* with MPG. They are NOT the same thing. ICE engines are most *efficient* at full-throttle, at mid-RPMs. That means they make the MOST HP for a given amount of fuel. But at that setting (peak torque) you are burning a LOT of fuel.

Your car will burn less fuel PER MILE at the lowest throttle opening that is above idle. My cars peaked at 35-45 MPH. My Imp and CX-5 both got 45 MPG at 40-45 MPH, summer temps, no wind.

It should be obvious that high-G accel burns more fuel per unit distance. You get to speed quicker, which then means you are burning more fuel due to higher air resistance, too.

For entering a busy highway, gas it! Safety overrides saving money. Park in the right lane, drive the speed limit, or slower if traffic allows. In heavy traffic, draft the car in front of you (leaving enough space to avoid rear-ending in a brake-check type emergency) while driving with the pack.

In the city, pull your head out of your ..., learn how to coast up to the next stop light, so you don't have to use your brakes. Don't worry about the idiots behind you, who want to drag race to the next red light.

Aggressive driving in the Impreza got 25 MPG. Driving per above, 36-38 MPG.

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: bobdoo] #5243596 10/18/19 05:16 PM
Joined: Feb 2019
Posts: 516
R
Railrust Offline
Offline
R
Joined: Feb 2019
Posts: 516
Agree 100%. My wife drives with a heavier foot than I do and let's just say this...we're averaging the SAME gas mileage in two different vehicles....but her's is a Honda CRV and mine is a full sized Chevy Silverado 4x4 V8 (both averaging almost identical MPG at 25). If she drove my truck she'd be averaging 18 at best.

Nothing gets me better fuel economy than slow takeoffs, coasting as much as possible and light throttle control when up to speed.

I easily get 30 mpg in my wife's vehicle by practicing light takeoffs and light throttle throughout the entire speed band.

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243597 10/18/19 05:16 PM
Joined: May 2012
Posts: 1,457
A
AVB Offline
Offline
A
Joined: May 2012
Posts: 1,457
There are also pumping losses, the engine actually has to work harder to draw in air the smaller the throttle opening is. One old hyper miler trick was to use large throttle opening, but limit the rpm by short and skip shifting when accelerating.

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243600 10/18/19 05:22 PM
Joined: Mar 2017
Posts: 11,313
PimTac Offline
Offline
Joined: Mar 2017
Posts: 11,313
The fuel economy on modern vehicles today is largely dictated by the transmission. While driver input with the right foot does have some effect, itโ€™s the computer programming of the transmission that optimizes the fuel efficiency regardless of throttle position. The transmissions shift up quickly to keep the engine in a narrow but fuel efficient range.

So it may not matter unless you are flooring the throttle.


2017 Mazda CX5
Havoline Pro DS 0w20
Roki OEM filter.
Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243605 10/18/19 05:26 PM
Joined: May 2012
Posts: 1,457
A
AVB Offline
Offline
A
Joined: May 2012
Posts: 1,457
Your foot also isn't directly opening the throttle, then throw in things like vvt and variable lift, variable intake runners and eco mode.

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243622 10/18/19 05:47 PM
Joined: Mar 2012
Posts: 816
T
tiger862 Offline
Offline
T
Joined: Mar 2012
Posts: 816
I keep mine in Eco mode. Transmission shifts faster depending on throttle input from gas pedal. You lightly push gas it is in high gear sooner and getting on interstate the difference between medium and hard acceleration changes lots of things from timing to transmission. It has taken me a while to get used to what Dodge calls intelligent transmission and it does help with fuel mileage at the cost of some driveability issues especially if you never drove one. It's all in the manual that most don't read which makes unnecessary trips to the dealership.

Last edited by tiger862; 10/18/19 05:47 PM.

Tiger862
2018 Grand Caravan
Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: onespiritbrain] #5243623 10/18/19 05:47 PM
Joined: Sep 2008
Posts: 4,397
G
gfh77665 Offline
Offline
G
Joined: Sep 2008
Posts: 4,397
Want MPG? Keep all your tires fully aired up, all the time.

Re: Fuel Mileage - Quick vs. Steady Acceleration [Re: Pelican] #5243637 10/18/19 06:16 PM
Joined: May 2019
Posts: 2,543
M
Mad_Hatter Offline
Offline
M
Joined: May 2019
Posts: 2,543
Originally Posted by Pelican
What's the other traffic doing while you "Take your time" to reach the posted speed?

Flipping him the bird!๐Ÿ˜‚

Page 1 of 2 1 2
Previous Thread
Index
Next Thread

BOB IS THE OIL GUY® Powered by UBB.threads™