The accelerator pedal and fuel consumption

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vw100
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The accelerator pedal and fuel consumption

Postby vw100 » Mon Sep 26, 2016 12:47 pm

Been watching the mpg numbers displayed on the trip computer while driving around town and i found that my right foot is f**k" heavy", AND no i am not heavy accelerating or anything, just driving relaxed in 2nd and stopping/slowing down constantly when the traffic requires it.
i never really cared about mpg numbers before, i just wanted to be smooth.
Any tips or tricks on using the accelerator pedal more efficently ?
I think the problem is accelerating from a stop to "cruising" speed (steady)
When building up momentum in 1st, do you guys roll on it continuously, or do you quickly press it and "wait" there until you gain enough speed to shift into 2nd ?
Again after shifting into 2nd and the rpm are at or just over idle but you want to accelerate to 2000rpm and keep it steady there, should i give it the amount required for 2000rpm and hold it there immediately after the shift, or should i roll on it :oops:

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Re: The accelerator pedal and fuel consumption

Postby IMBoring25 » Mon Sep 26, 2016 1:26 pm

Mileage while accelerating to cruising speed is going to stink. That's just the way it is, and I've found going too crazy with gentle acceleration can be as bad as the proverbial jackrabbit starts, at least in my vehicles. Moderate seems to be the way to go, though something below what seems moderate may be appropriate in turbocharged applications.

Actually, most of the potential for improving MPG is in how you slow and stop. Increase following distance and look far ahead and get off the gas as soon as you anticipate a need to slow. If a light has been green for a long time be prepared for signs it might turn red before you get there and consider coasting immediately (but don't induce road rage in those behind you). If you get in the mindset that having to use the brakes is a mild failing, it can be a rather fun game and will save you money on gas, tires, and brakes. Provided you use enough brake to light the brake lights or use emergency flashers, spreading out your speed differentials may even help prevent getting rear-ended.

I generally try to have the throttle at the"neutral" position for the gear and speed any time the clutch is moving so there is no load through the transmission for the smoothest shift. Any changes are rolled in and out. I do usually reach a level of acceleration I'm happy to keep using in time for a steady-throttle time before it's time to roll out throttle for the next shift. All this, though, pretty much amounts to personal preference.

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Re: The accelerator pedal and fuel consumption

Postby theholycow » Mon Sep 26, 2016 2:17 pm

IMBoring25 wrote:If you get in the mindset that having to use the brakes is a mild failing, it can be a rather fun game and will save you money on gas, tires, and brakes.

^This. Brakes are devices for discarding energy...energy that you spent fuel to make. If you can plan better to avoid discarding energy then you will reduce your fuel consumption because you won't need to burn that fuel in the first place. Besides waltzing slowly through a fresh green light instead of rushing up to come to a dead stop and wait, a favorite of mine is not slowing for curves or turns any more than necessary...that one is fun, and successfully shakes off most tailgaters. Of course in any kind of stop-and-go traffic, idle along in 1st with lots of lead space instead of riding the bumper in front of you and exercising your legs excessively.

As far as what you can do with the accelerator pedal to improve fuel economy, that varies by vehicle. In my experience, most normally aspirated (non-turbo) vehicles respond well to heavy throttle and low RPM, shifting early enough to prevent excessive acceleration rate (and I understand that most turbo vehicles respond better to a light foot). The travel rate of your foot on the pedal while pressing it deeply, in a carbureted vehicle or primitive fuel-injected vehicle, should be gentle to prevent the accelerator pump (or computer-simulated software facsimile) from squirting a bunch of liquid fuel; but modern vehicles should all be smart enough to avoid that.

Anyway, an open throttle successfully accomplishes what so many intake upgrades promise but fail to deliver: Reduced restriction. Sucking air through a tiny opening uses more energy than sucking the same amount of air through a larger opening (this is part of what is called "pumping losses"). There are other ways that it helps the engine convert fuel into energy more efficiently, and as a whole the effect is measured in a metric called Brake Specific Fuel Consumption. For popular engines you can sometimes hit up Google Image Search for a BSFC map to show you the very most efficient RPM and throttle opening, usually 75-100% open throttle and RPM somewhere below that engine's torque peak.

Of course, a turbo throws a wrench in that whole works.
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Re: The accelerator pedal and fuel consumption

Postby tankinbeans » Mon Sep 26, 2016 5:23 pm

I end up accelerating moderately quickly, am usuallybfirst off the line, and pull decent numbers. I've found that the less I think about it the better. When I hear the "shift at 2000 rpm for best mileage" I get hives. That's too much mugging the tach for my comfort.
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Re: The accelerator pedal and fuel consumption

Postby Rope-Pusher » Mon Sep 26, 2016 9:06 pm

I try to plan my driving to avoid applying the brakes until I've coasted 10 mph under the speed limit and I typically drive just less than 10 mph over the speed limit, so there is a potential of coasting down ~20 mph for unavoidable stops. Does this sound like the "pulsing" that hyper-milers do?

I tend to shift early and apply a lot of throttle at low rpms to accelerate.

Pump a few more slices (anyone know where I got this phrase from?) into your tires than the recommended pressure - it usually makes for sharper turn-in and better handling overall in addition to reducing the rolling resistance.

Leave the ac off AND the windows rolled up nearly all the way.
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Re: The accelerator pedal and fuel consumption

Postby theholycow » Mon Sep 26, 2016 9:48 pm

Rope-Pusher wrote:I try to plan my driving to avoid applying the brakes until I've coasted 10 mph under the speed limit and I typically drive just less than 10 mph over the speed limit, so there is a potential of coasting down ~20 mph for unavoidable stops. Does this sound like the "pulsing" that hyper-milers do?

Nope. Hypermiling pulse&glide is more insistently cyclical; produce energy at best BSFC until speed is too great, then coast (neutral; not engine braking) until speed is insufficient, rinse and repeat. Works best if you can match it up to short, mild, rolling hills, where you can keep an almost perfectly steady speed so as not to have to worry about fitting the whole thing in with speed limits and other drivers.

Pump a few more slices (anyone know where I got this phrase from?) into your tires than the recommended pressure - it usually makes for sharper turn-in and better handling overall in addition to reducing the rolling resistance.

"Slices" almost rings a bell...something to do with looking at a gauge dial as if it was a pie chart?

Anyway, a little extra air (probably not to exceed the tire's maximum as molded into the sidewall) improves all those things and more...notably, longer treadwear and better road hazard existence in my experience.

Leave the ac off AND the windows rolled up nearly all the way.

An uncomfortable driver is an inefficient, inattentive, stressed, and hurried driver. Gotta manage the wetware.
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Re: The accelerator pedal and fuel consumption

Postby Rope-Pusher » Tue Sep 27, 2016 8:12 pm

Cow, I'm not a crazy rolling roadblock like true hyper-milers, but I am pulsing nonetheless.



Being comfortable is a state of mind. I can ignore being hot or cold to a great degree. It's like a runner who ignores when his lungs and legs are aching.

The amount of energy consumed by the AC compressor, the HVAC blower and the cooling module fan, all of which operate when I run my AC, is significant.
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Re: The accelerator pedal and fuel consumption

Postby vw100 » Thu Sep 29, 2016 2:45 pm

Rope-Pusher wrote:I tend to shift early and apply a lot of throttle at low rpms to accelerate.

isn't that the recipe for lugging :?: i feel guilty every time i do that :oops:

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Re: The accelerator pedal and fuel consumption

Postby IMBoring25 » Thu Sep 29, 2016 3:06 pm

It should make noises that indicate it doesn't like what you're doing before it gets to the point of hurting anything.

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Re: The accelerator pedal and fuel consumption

Postby theholycow » Thu Sep 29, 2016 4:24 pm

vw100 wrote:isn't that the recipe for lugging :?: i feel guilty every time i do that :oops:

This combination of guilt, fear, uncertainty, and doubt is why I used to always go on about the lugging thing...until one particular user took umbrage.

So, give it whatever name you want but if the car isn't obviously complaining and is functioning as intended then don't worry or feel guilty, just do what you want...try to save fuel if you want, or don't if you don't want. You're not going to hurt anything without being clearly told so by your engine before it's too late.
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Re: The accelerator pedal and fuel consumption

Postby vw100 » Fri Sep 30, 2016 1:05 pm

theholycow wrote:This combination of guilt, fear, uncertainty, and doubt is why I used to always go on about the lugging thing...until one particular user took umbrage.

So, give it whatever name you want but if the car isn't obviously complaining and is functioning as intended then don't worry or feel guilty, just do what you want...try to save fuel if you want, or don't if you don't want. You're not going to hurt anything without being clearly told so by your engine before it's too late.

well sure if it judders violently and makes obvious noises, it is letting you know you are doing things wrong.But in low gears (2nd), it will feel just a bit sluggish for a second until it builds revs. That's when i get nervous :?

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Re: The accelerator pedal and fuel consumption

Postby theholycow » Fri Sep 30, 2016 3:14 pm

vw100 wrote:well sure if it judders violently and makes obvious noises, it is letting you know you are doing things wrong.But in low gears (2nd), it will feel just a bit sluggish for a second until it builds revs. That's when i get nervous :?

Don't get nervous (unless you are being pursued by a convoy of Mack truck driving zombies, quickly catching up; then you should downshift and stand on it).

If it's not obvious that something is bad about your low RPM acceleration then nothing is bad. If it's just growling then that's a warning that you are mildly pushing the envelope and should choose slightly higher RPM next time, but unless you're growling down the road for a long time then you don't need to panic out of the current gear, you can just wait out a little growl if you want (or you can use it an excuse to practice downshifting).
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Re: The accelerator pedal and fuel consumption

Postby tankinbeans » Fri Sep 30, 2016 9:41 pm

Cow, would the added variable of electronic throttle throw an added wrench into the gears? I can't remember the last time I've driven a vehicle with a cable throttle, much less owned one. Driving with moderate acceleration usually nets me mixed mileage estimate, if not slightly better.
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Re: The accelerator pedal and fuel consumption

Postby theholycow » Fri Sep 30, 2016 10:10 pm

That depends on how obedient it is.

Actually, the one thing I liked about the know-it-all smartass busybody throttle in my VW was that it did the wide throttle thing whether I did or not. I'd watch the TPS reading as I lightfooted it, keeping RPM low, and it would open the throttle most or all of the way while I merely feathered the accelerator pedal.
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Re: The accelerator pedal and fuel consumption

Postby Rope-Pusher » Sat Oct 01, 2016 2:55 pm

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