Save fuel, but what about the wear?

[LucasDK]

Hi,

Here in Europe there is a lot of public/governmental information on how to save fuel. Somehow politicians have realized that too much fuel is used because people do not drive their cars properly. One of the major points is:

Accelerate quickly and reach your final cruising speed as quickly as possible. This requires rapid gear shifts pushing the throttle pedal to approx 75% (but never 100% - it really should be between 50 and 100%) of full depression.

They made tests and have shown that indeed you will save fuel if you compare this driving style to the old fashioned driving style where you slowly increase speed.

However, and this is my question: I don't like accelerating too fast, especially when the engine oil is cold. Maybe I'm wrong, but I believe that fast accelerations increase wear because of the tremendous stress on the engine parts.

What is your opinion on that topic?

Lucas

 

[heyu]

Interesting odd survey but all vehicles are different ,,I'm sure you have nothing to worry about as long as they are not recommending to break the tires loose and spin your tires every time,,But the jackrabbit takeoffs all the time i would think would strain the transmission if anything

 

[tommygunn]

If the engine is cold I wouldn't either. Whats important to realize though is they don't mean high RPM acceleration, they do however mean a high amount of throttle.

"What the [censored] are you on about?"

Easy. With the accelerator to the floor your engine experiences no loss trying to suck air past the throttle plate and develops maximum efficiency. At high RPM its using tons of fuel, but, for the power you get, its most efficient. But you don't want RPMs.

The best way to use this is to shift as early as possible and accelerate in higher gears, slowly, with 75% of full throttle. The RPMs stay low, acceleration isn't a race, the engine saves on pumping losses (no throttle restriction) and develops maximum efficiency per stroke.

As soon as you can upshift into a new gear without stalling (and some extra margin of course), do it, and deal with having to push your foot further down to accelerate. Its easily proven to increase efficiency, and thus, mileage.

And of course, the sooner you get into a higher gear, the better, always, but there's no need to "race" up to speed to get there. If you can upshift, do it, always. The problem is people loaf around in low gears slowly accelerating it causes losses, and some people don't even hit fourth or fifth in city driving...or at least not around here...because they're lazy and would rather avoid extra shifting.

 

[dnewton3]

Way too general a statement to make than I would accept.

My personal experience does not bear this out; I get better economy by being frugal on the throttle.

There is a "sweet spot" for almost any engine, be design and manufacture, where peak efficiency comes into play, and technically that is often where the BSFC is maximized. We cannot just make and accept a blanket statement that all vehicles are going to be more efficient when accelerating at 75% throttle. Much of it has to do with how that power is not only generated, but transfered to the ground. Efficiency losses such as transmission slipping (auto vs manual shift vs CVT), thermal effiency of the cycle (cold vs warm engine), etc, etc all play into account.

Same bovine-poo exists with the whole "use a/c and not drive with windows down" topic. Some vehicles are going to be more efficient with the a/c on, while others are more efficient with the windows down. Because there are thousdans of different combinations of cars, trucks, vans, roads, drivers, seasons, tires, headwinds, etc, etc, we cannot accept a blanket statement as true for all.

Typical government approach to most things; make a "one size fits all" statement after months (if not years) of committee meetings so that the real truth is whitewashed down into nearly unusable information.

 

[heyu]

Originally Posted By: tommygunn
If the engine is cold I wouldn't either. Whats important to realize though is they don't mean high RPM acceleration, they do however mean a high amount of throttle.

"What the [censored] are you on about?"

Easy. With the accelerator to the floor your engine experiences no loss trying to suck air past the throttle plate and develops maximum efficiency. At high RPM its using tons of fuel, but, for the power you get, its most efficient. But you don't want RPMs.

The best way to use this is to shift as early as possible and accelerate in higher gears, slowly, with 75% of full throttle. The RPMs stay low, acceleration isn't a race, the engine saves on pumping losses (no throttle restriction) and develops maximum efficiency per stroke.

As soon as you can upshift into a new gear without stalling (and some extra margin of course), do it, and deal with having to push your foot further down to accelerate. Its easily proven to increase efficiency, and thus, mileage.

And of course, the sooner you get into a higher gear, the better, always, but there's no need to "race" up to speed to get there. If you can upshift, do it, always. The problem is people loaf around in low gears slowly accelerating it causes losses, and some people don't even hit fourth or fifth in city driving...or at least not around here...because they're lazy and would rather avoid extra shifting.


I am on about THE MAIN QUESTION Quote----->>>I don't like accelerating too fast, especially when the engine oil is cold. Maybe I'm wrong, but I believe that fast accelerations increase wear because of the tremendous stress on the engine parts...

Unless there is tire burning starts (exaggerated) there will be no tremendous stress on the engine parts ,,,,,any tremendous stress would be the clutch (if anything)The engine reaches oper temps in at least 5 min therefore all should be good----

There was no question about shifting it is already confiqured before the main question

 

[UNC151]

Thoughts about wear aside, based upon my experience while driving a 2011 F-150 Ecoboost I had as a loaner, this does not pan out. I approached 26MPG by feathering the throttle on take-off and gradually increasing speed.

This model has an "instant mpg" LCD indicator that I reset when I picked up the truck so that I could experiment with it. Light throttle and gradual increases were the only way that MPG would remain on the uptick until it peaked at 25MPG. I wish that I would have had it another week so that I could have seen what the maximum MPG would have been, but also to "teach" myself the habits so that I could transfer that into driving my FX4.

Fast acceleration guarantees the MPG will suffer in almost every situation (IMHO).

 

[supton]

I don't think many people understand the operation of the scientific method. Formulate a hypothesis, test, test it some more to see if it breaks. IOW, try 3 tanks of fuel with high throttle/low shift points, then three tanks of fuel with frugal throttle: and run with what gets the desired results.

IMO, cars today, unless if junk to begin with, can take a flogging dead-cold. Unless if it's below 0F I'm not sure if the rest of the car will care. Afterall, they are designed to do cold starts at -40C/-40F routinely.

My diesel seems to care not one whit about what I do at low speeds; I think it'll idle for hours. It looses mpg's instead on the highway, and a/c doesn't help. But I'd go nuts with a window open, so I'll gladly take that mpg hit. Since I don't have a throttle plate the notion of short-shifting at high throttle openings doesn't apply (no pumping losses) but I suspect high(er) rpm is more lossy. And in hot weather, with the a/c on, the turbo lag is almost dangerous (get on it hard and once the rpm's take climb it can suddenly take off).

Too bad most cars aren't built for mpg--you know, a transmission that would allow you to pick the right gear. I was saddened to see in a rental Camry that the automatic would not hold a gear in sport mode: step on the throttle and it'd still downshift, even for a light throttle application.

 

[Samilcar]

Originally Posted By: LucasDK

Accelerate quickly and reach your final cruising speed as quickly as possible. This requires rapid gear shifts pushing the throttle pedal to approx 75% (but never 100% - it really should be between 50 and 100%) of full depression.

They made tests and have shown that indeed you will save fuel if you compare this driving style to the old fashioned driving style where you slowly increase speed.


I have found this to be definitely true only on one of our vehicles (the heaviest vehicle with the most powerful engine). Accelerating slowly up to target speed using ~10% throttle returns poor overall fuel mileage. Using ~50% throttle to get up to the same target speed returns overall better mileage. Either this isn't true with our other vehicles, or the mileage difference is so small that it isn't noticeable.

I think this is somewhat similar to hypermilers that use the "pulse and glide" technique.

 

[HerrStig]

I wonder what's cheaper, the purchase, care and feeding of a 9 speed auto, or a litle more gas to run a 5 speed.

 

[JHZR2]

I have always found that a light foot provides the best economy. However, being too light of a foot means that youre spending a lot of time accelerating versus cruising at steady state.

Remember back to calculus... Speed is first derivative of position, and acceleration is second derivative. It is the change in time of the change in time of position - the change in speed wrt time. In order to affect that change, more power is needeed than if that rate of change in speed was zero. Thus it takes more fuel to accelerate through a speed level than to sit there.

So what happens practically when accelerating too slow is that you are using excess fuel as compared to sitting at any given rate of speed, but not getting to any new rate of speed fast enough to hit a steady state cruising speed, which is more efficient as there is no "overpotential" of power use.

Accelerate too fast on the other hand, and the "overpotential" required to get such a high rate of change is less efficient on a momentary basis, and creates thermal, compressive, torsional and other stresses on the engine. So youre burning more fuel, doing more work, just to get to the same end goal, meanwhile not taking advantage of the mechanical advantage provided by changing ratios in the gearset.

Ive read that the optimal condition is wide throttle at low engine speed (just barely lugging) with smooth acceleration.

At least in the USA, the proliferation of television and automatic transmissions have made people so dumb in terms of driving skill that they all mash the go pedal and rocket from a stop. Its amazing how much faster a Toyota Sienna is off the line than my 135i... It just blows me away. Maybe someday Ill have a vehicle as fast and powerful as a sienna.

 

[JHZR2]

Originally Posted By: HerrStig
I wonder what's cheaper, the purchase, care and feeding of a 9 speed auto, or a litle more gas to run a 5 speed.


How about the selection of a good set of gear ratios.

So the dolts driving 4 cyl engines dont have to be fooled into thinking that their econobox has "good pickup", like the ridiculous 1st gear ratio in many, and so the driver may need to do an extra shift here or there but can get a real good OD or two in the 5-6 speed MTs that most every car should have???

 

[Artem]

Just like accelerating slowly while in the "sweet spot", accelerating quickly also has a sweet spot.

You simply can't just hammer the throttle right off the line and hope for the best. You still have to take off gently and increase the throttle as the speed picks up. Its hard to explain.

I drive VERY aggressively and have proven this in two completely different cars, my 2007 Civic Si 6speed and a 2006 Scion tC 5speed. Both cars achieve a few points away from their rated highway MPGs while doing mostly city driving with Very quick take offs, high RPMs, full throttle and lots of downshifts to pass slow moving turtles.

My tC is rated for 19 city/27 hwy mpg and i average 25-26mpg with each and every fill up while flying through the city 90% of the time. The car is also modified and has wider wheels and tires compared to stock and still get awesome MPGs on a daily basis. I've yet to try to go a week without flooring it to see if i can get better MPGs because quite frankly... why? I'm satisfied with the MPGs i get based on the driving style / conditions so i just continue living in the fast lane.

Keep in mind that i use ALLOT of hypermilling techniques after i've already got up to speed, so i feel that also plays a big role in the good gas mileage i get.

 

[Cujet]

If you drive a diesel, moderate acceleration will get you up to cruising speed (the most efficient speed) without wasted fuel.

However, in modern gas cars, the air/fuel ratio is enriched from 14.7/1 (many cars run 14.2/1) to 12/1 (or richer) when acceleration levels of power are called for. This directly translates into wasted fuel and poor economy.

If you have a scan-gauge or other A/F display, keeping the engine at stoic during accel will result in better fuel economy. This requires keeping your foot out of it.

Having done significant tuning, the best fuel economy is achieved at between 16.2 and 17.5 to 1. Generally requiring a larger throttle opening for the same output.

 

[Jim Allen]

I'm in the moderate acceleration to cruise camp.

I have an instant MPG readout. I have experimented alot.

Say I want to accelerate to 55.

I accelerate sedately, keeping the readout as high as possible... e.g 9.25 mpg. It takes me 35 seconds to reach 55. At 55, my mpg levels to 19.5 mpg.

I accelerate more aggressively (but not excessively aggressively) and my readout says 6.5 mpg. It takes me 18 seconds to reach 55 and I attain the same 19.5 @ 55 mpg.

Did I use more or less fuel accelerating for 35 seconds at 9.25 mpg than I did accelerating for 18 seconds at 6.5 mpg?

These are pretty accurate figures for my F150 and strictly going by the average mpg readout, I do better by accelerating more briskly, getting the truck shifted up into the higher gears sooner, locking the convert and using that BSFC to my advantage. Actually, I accelerate briskly until it shifts into OD, then I back off a little and let the converter lock, then a accelerate as hard as I can without the converter unlocking.

I actually have the BSFC graph for my 5.4L engine and know it's at it's lowest level at 2000 rpm but it's low and level from 1500-3000 rpm, so I operate in that range. I have adjusted my shift points lower (and downshift points higher) as well to take advantage of that, as well as changing the pedal slope so that danged electronic throttle is less sensitive..

 

[Vikas]

Few snarky comments

- 5-speed tC rated 19city? Did it come with a V10 from factory??

- 35 seconds to reach 55mph and you are still alive to tell us about it! There are some guys who consider anything slower than 6 seconds from 0-60 means they will get run over when merging on the highway.

Seriously, Jim has given real life explanation with data to support how brisk acceleration can indeed save the fuel.

 

[tommygunn]

I like how I post a long technical breakdown of how more throttle can be more efficient and someone other then the OP manages to [censored] me out saying what I'm talking about was never in question.

Hijack a thread much?

 

[CATERHAM]

Originally Posted By: LucasDK
Hi,

Here in Europe there is a lot of public/governmental information on how to save fuel. Somehow politicians have realized that too much fuel is used because people do not drive their cars properly. One of the major points is:

Accelerate quickly and reach your final cruising speed as quickly as possible. This requires rapid gear shifts pushing the throttle pedal to approx 75% (but never 100% - it really should be between 50 and 100%) of full depression.

They made tests and have shown that indeed you will save fuel if you compare this driving style to the old fashioned driving style where you slowly increase speed.

However, and this is my question: I don't like accelerating too fast, especially when the engine oil is cold. Maybe I'm wrong, but I believe that fast accelerations increase wear because of the tremendous stress on the engine parts.

What is your opinion on that topic?

Lucas

Yes it is counter-intuitive but I've read the same thing in hypermilling techniques. Keep in mind you are still short shifting at very low rev's (shifting at 2,000-2,500 rpm )so you're not accelerating all that fast. The key to maximizing fuel economy seems to be keeping the rev's down but not low throttle openings when accelerating.
Because of the low rev's the technique won't have any adverse affect on cold engine wear.

 

[mechtech2]

A car will accelerate pretty fast with minimal throttle openings.
Because WOT is not needed at low/medium RPM. I can hardly tell the difference from full throttle and 1/4 at low engine speeds.

Of course, driving in too low a gear is not good for anything - upshift as soon as you can.

 

[SteveSRT8]

This technique is only effective in micro ssized engines that you can open the throttle on.

Does nothing for a large displacement motor in a hi po auto.

FWIW I had a 99 vette that easily got 21 mpg in town. Not bad for a 185 mph car.

 

[JamesBond]

BMW's eta engine of the 80's was designed around the idea of using high throttle openings and low rpm shifting to create sufficient power while returning high mpg. I read an article many years ago about that engine returning the best mpg with high (3/4) throttle openings and low rpm shifting. (Sorry no source on that)

I have an e30 with the eta engine and have found that driving in that manner is not always practical in this, or any other car, due to the limitations of traffic, stop lights/signs, speed limits etc. In most cases I just try to go with the flow of traffic in order to not confuse the other idiots on the road.