Better Fuel Economy When Driven Hard?

[Brodes]

I've been calculating my fuel consumption by using the odometer/full-fill method for the past year or so now and I'm finding the trend that when I drive grandma mode in an attempt to save fuel I get lower economy (~15-16L/100kms) than when I drive aggressive (~13-14L/100kms). This is in my stock auto EL XR8. Quite interesting and I know there are a few variables at play.

Does anyone else find the same? What's your theory?

[pottery beige]

its telling you stop driving like a nanna

old banger XE is much the same

drive harder, makes more noise, doesnt go much faster, drinks the same

aliens

[Bushbasher]

The engine doesn't run efficiently till you get above 60kph. Until then your usage is crap as far as fuel burned for distance covered so you want to get up to speed in a reasonable amount of time so your engine can be in lean burn cruise mode for longer. The trick is to find the point where acceleration isn't so hard that is negates the overall economy.

25-30L/100 for 5 seconds acceleration will use less fuel than 18-23L/100 for 10 seconds but giving it the welly and getting 50+L/100 for 4 seconds is going to be worse than 18-23L/100 for 10 seconds so you need to find the happy medium if that makes sense .

[Jack960]

When you put your foot down and go wide open throttle there are much less pumping losses, if you drive like a grandma and accelerate slowly with a slightly open throttle the pumping losses increase. Technically Engine's are more efficient when running wide open throttle, unless it doesn't use a throttle of course.

[EA2BA]

I have generally always found, driving for economy, or drive it hard, pretty much no difference in fuel economy, if the car is reasonably tuned and looked after it, drive it how you want and don't worry about it.

[Silver Ghia]

Originally Posted by Bushbasher

The engine doesn't run efficiently till you get above 60kph. Until then your usage is crap as far as fuel burned for distance covered so you want to get up to speed in a reasonable amount of time so your engine can be in lean burn cruise mode for longer. The trick is to find the point where acceleration isn't so hard that is negates the overall economy.

25-30L/100 for 5 seconds acceleration will use less fuel than 18-23L/100 for 10 seconds but giving it the welly and getting 50+L/100 for 4 seconds is going to be worse than 18-23L/100 for 10 seconds so you need to find the happy medium if that makes sense .

That's what I found with my AU Fairmont and BA Ghia.

[Bushbasher]

Originally Posted by EA2BA

I have generally always found, driving for economy, or drive it hard, pretty much no difference in fuel economy, if the car is reasonably tuned and looked after it, drive it how you want and don't worry about it.

I disagree, whenever my missus gets into my car and drives it my economy average goes up, or is it down...., anyway, she uses more fuel, and whenever I drive her wagon I can manage to get 20-30km a tank more out of it than she does. She ALWAYS uses more fuel than me no matter what car she's driving because of her driving style. She accelerates too hard and drives into corners, or "stab and steer" as I call it. I on the other hand roll out of the throttle and coast up to corners and keep my mid corner speed up then squeeze the throttle on exit rather than stab it open. Driving style makes a difference for sure but jambing open the throttle and hard acceleration wastes more fuel as the engine RPM then needs to catch up with how much fuel it's being fed .
As an example, early cruise control didn't have the 40kph lock out and it was found that if you set the CC once you were doing warp speed then disengaged it then stopped, you could get the CC to take off from stand still and do a standing quarter faster than if you did a regular foot to the floor take off. This was because the CC didn't floor it, it progressively squeezed the throttle open using the ECU to keep the mixtures right thus getting a clean burn right through the rev range instead of running rich off of idle till the revs got high enough to pass enough air to burn all the fuel it was being given. The CC went quicker and used less fuel doing it.
This, combined with the engines natural Torquay nature allows you to get up to speed on less than 1/4 throttle quickly enough where using 1/2 throttle will use more fuel and not save much time and conversely, using granny mode on the throttle forces the engine to run less efficiently, because it can't use its' torque, for longer which ultimately uses more fuel.
Squeeze and run rather than stab and steer, and find the happy medium to take advantage of the engines torque and you'll get your best economy. drive like you're racing for first place or always running late and it'll cost you at the bowser.

Works for me...........

[Brodes]

I guess there's also the fact that when I'm in agro mode I miss more red lights.

[danzvtil]

Any Falcon or Magna 6 cyl ive ever driven hard has come with a large fuel increase, Im sure small cars today are the opposite. Case in point, my 1.6 GDI Rio and 1.4 Turbo Cruze work car both fail to use more fuel or decrease tank range when going for an extended burn thru the twisties.
These same 2 cars seem to be tuned for suburban running at 60-90kph, a run on the highway at 100-110 sees them get the same per tank as city driving.

[MattSAU2XR8]

I'm not too sure about the 'pumping losses' theory. When you think about it cars spend about 95 % of their time traveling at cruise speed, be it 60, 80, 100 or 110 k/h with the throttle nearly closed. So whether it is 1/4 or 1/2 open the other 5 % of the time shouldn't make all that much difference. Accordingly, if I'm driving my FG Ecoboost up a moderately steep hill at constant speed the 'instant economy' is about 13 l/100 km, increases to 20 with a little more throttle, then 30, 40, and 50 as I push progressively harder.

What probably does save money is a slightly lower cruising speed. Wind drag is proportional to velocity squared, so at 110 km/h you could expect to burn 21 % more fuel per time. Although you would be travelling 10 % faster so the end result is about 11 % more fuel per distance.

The other thing which I'm pretty sure makes a difference is hills. Its pretty hilly on my way to work and so my average fuel economy is pretty poor at 10 l/100 km with the aircon on. I'm pretty sure this would drop close to the advertised 8.5 if I were to sit under the speed limit, not have any hills, and not use the aircon.

[yearby]

When I drive my nephews 5 speed BF xr6 ute, I get about 6.9 L/100 at 80km/h, when I drive it at 100km it gets 12 L/100.

But when I drive my BF GT 6 speed auto at 80Km/h it gets 12L/100 and at 100km it gets 6.9 L/100 Huh????

That's watching the instantaneous fuel usage level.
Maybe I need to put in a lower diff ratio (higher numbered ratio) to increase my fuel economy ????

Peter.

[damo76]

well my 351 clevo doesn't have better fuel economy when driven hard lol.

[EA2BA]

Originally Posted by Bushbasher

I disagree, whenever my missus gets into my car and drives it my economy average goes up, or is it down...., anyway, she uses more fuel, and whenever I drive her wagon I can manage to get 20-30km a tank more out of it than she does. She ALWAYS uses more fuel than me no matter what car she's driving because of her driving style...........

Perhaps my style doesn't change much, just the amount of pedal to get to speed is more swift, hit speed quicker then jump off the loud pedal.

Maybe it evens out then and so no noticeable change is to be had.

[castellan]

Well some will say that the slower you drive the better it will be on fuel, well that is true to a point but not always.

The harder the engine has to work the more it will use.

If you have enough brain power to work out that riding a pushy is something alike so you ride at a speed you feel comfortable with and if you come to a big hill you would go faster down a hill before it starts going up hill, so you don't work yourself so hard, don't you.

Same with a car on the highway doing 100 km/h, I like to let it go a bit faster down hill then just keep my foot still at a point I think it need be and let it drop speed to the top maybe even to 80km/h, if no one is being held up behind me that is.

I have a 6sp manual and on some roads that are hilly I will use 5th gear as the engine is not working as hard out of it's torque range especial with the bike in the back of the ute or a lot of weight.

Putting the boot into it will only chew the fuel and if that's not true there is something wrong with the tune, or lacking power down low.

I once had a 308 that I think it some times was like it swallowed fuel by the hour, it did not matter driving at 100 km/h or 180km/h that much and use a bit more up to 215km/h flat. sitting at the red lights I could see the fuel gauge dropping I am sure. and it could get 22 mpg at 100 to 140 km/h highway driving for fuel economy.

Some cars if you pussy foot them around will not be good on fuel mainly because they are gutless or the driver is just a fool.

[baboon]

I find locking the converter gives better economy.

[CoupeKing]

Well I just cruise along, especially in between lights. But I found that keeping the correct tyre pressure saves some fuel. Only noticed it on the highway though, easier to measure.

[blackf6]

Under 60km/hr tire pressures play a large part in fuel economy. Over 80km/hr aerodynamics plays the largest part in saving fuel. Keep your tire pressures right. Check pressures when cold so as to not over inflate. Keep the vehicle rolling along with the least gear changes and stopping as possible.