What is more fuel efficient...
06-26-2008, 03:56 PM
#1
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What is more fuel efficient...
First Case:
1. Driving 60 km/h in fifth gear with revs around 1500 RPM and maintaining moderate to heavy throttle to keep the speed.
2. Driving 60 km/h in third gear with revs around 3000 RPM and maintaining light throttle to keep the speed.
Second Case:
1. Coasting down a hill in gear, my TDS-1 indicating high vacuum.
2. Coasting down a hill in neutral, the engine idling. The TDS-1 indicates small vacuum.
I've gotten into the habbit of accelerating full throttle (because I like to) and then once I hit the speed limit I change gear into neutral and let the car coast down the road while idling (because I'm poor and want to save gas).
So what is most fuel efficient in these two cases?
1. Driving 60 km/h in fifth gear with revs around 1500 RPM and maintaining moderate to heavy throttle to keep the speed.
2. Driving 60 km/h in third gear with revs around 3000 RPM and maintaining light throttle to keep the speed.
Second Case:
1. Coasting down a hill in gear, my TDS-1 indicating high vacuum.
2. Coasting down a hill in neutral, the engine idling. The TDS-1 indicates small vacuum.
I've gotten into the habbit of accelerating full throttle (because I like to) and then once I hit the speed limit I change gear into neutral and let the car coast down the road while idling (because I'm poor and want to save gas).
So what is most fuel efficient in these two cases?
06-26-2008, 04:36 PM
#4
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Re: What is more fuel efficient...
First case: Option #2.
Second case: Option #1.
First case caveats: If possible, I would accelerate before the uphill grade to say 110kph so you use less throttle and also remain in a higher gear as you climb the hill.
Second case caveats: Rolling in gear means your injectors are shut off until the RPMs drop low enough that the engine begins to add fuel again to maintain idle. So you'd want to clutch in at about 1000 RPM.
However, rolling in gear will decrease your coasting distance due to the extra rotating masses involved. If it is practical to shut off your engine for atleast 20 seconds, and you are prepared to not have power steering and brakes, you can shut off your engine for even more economy. The problem with this is that the starter likes to operate while cool, if you repeatedly start your engine while hot, it might decrease the life of the starter.
Second case: Option #1.
First case caveats: If possible, I would accelerate before the uphill grade to say 110kph so you use less throttle and also remain in a higher gear as you climb the hill.
Second case caveats: Rolling in gear means your injectors are shut off until the RPMs drop low enough that the engine begins to add fuel again to maintain idle. So you'd want to clutch in at about 1000 RPM.
However, rolling in gear will decrease your coasting distance due to the extra rotating masses involved. If it is practical to shut off your engine for atleast 20 seconds, and you are prepared to not have power steering and brakes, you can shut off your engine for even more economy. The problem with this is that the starter likes to operate while cool, if you repeatedly start your engine while hot, it might decrease the life of the starter.
06-26-2008, 06:48 PM
#6
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Coasting as much as possible
I get an extra MPG on my commute with liberal coasting. Not the right way to drive or the safest way but I been averaging a 1-1.5 per tank more when doing it..
06-26-2008, 07:10 PM
#7
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In gear coasting is more efficient. In neutral the engine is injecting to maintain RPM
While coasting the engine is injecting barely any fuel since it the interia is maintatining engine revs.
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06-26-2008, 09:40 PM
#8
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More questions. How do revs and throttle amount effect fuel use? Are there any basic rules?
1. Should I always keep the revs in a certain range?
2. If the engine is having no trouble maintaining the speed, should I always select the highest gear possible (like 5th), or is it better to always keep the revs around 3000 or so, etc. Do I always select the highest gear possible that doesn't cause the engine to struggle?
3. Is it better to accelerate in second gear to my desired speed with ease, or to accelerate in third a little slower?
4. Can I assume that cruising at 50 km/h in second gear (tach needle pointing straight up) consumes more fuel than cruising in third? What if I need to accelerate, would a fast effortless 2nd gear burst be better than a slower third gear pull?
5. If coasting in gear gives better mileage, then should I allow engine braking to take place, or supply a little gas to prevent it? It seems strange to have the car slowing itself down when I want to coast as far as possible. I'm not about to turn anything off. :-)
6. Assuming I'm coasting in gear, is it better to be in a higher gear with lower revs, or a lower gear with higher revs? For instance, if I'm approaching a stop sign and my current speed is great enough that I'll reach the sign in any gear regardless of engine braking, should I switch to a higher gear during the coast, or maintain a lower gear?
Thanks.
2. If the engine is having no trouble maintaining the speed, should I always select the highest gear possible (like 5th), or is it better to always keep the revs around 3000 or so, etc. Do I always select the highest gear possible that doesn't cause the engine to struggle?
3. Is it better to accelerate in second gear to my desired speed with ease, or to accelerate in third a little slower?
4. Can I assume that cruising at 50 km/h in second gear (tach needle pointing straight up) consumes more fuel than cruising in third? What if I need to accelerate, would a fast effortless 2nd gear burst be better than a slower third gear pull?
5. If coasting in gear gives better mileage, then should I allow engine braking to take place, or supply a little gas to prevent it? It seems strange to have the car slowing itself down when I want to coast as far as possible. I'm not about to turn anything off. :-)
6. Assuming I'm coasting in gear, is it better to be in a higher gear with lower revs, or a lower gear with higher revs? For instance, if I'm approaching a stop sign and my current speed is great enough that I'll reach the sign in any gear regardless of engine braking, should I switch to a higher gear during the coast, or maintain a lower gear?
Thanks.
06-27-2008, 06:04 AM
#9
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Wow, you're just full of questions. They're all good ones too.
When accelerating keep the revs between 2-4k. This is the peak of the torque curve and the engine's most efficient range for accelerating. Accelerate with as close to WOT as traffic and conditions will allow. This will allow the engine to opperate near it's most efficient state (WOT @ the torque peak RPM.) I usually shift out of first quickly and get on the gas hard in 2nd and maybe 3rd too if I'm going to be cruising at a higher speed than the normal 50mph.
Once you reach you cruising speed let off the gas and shift into 5th from what ever gear you were in. No need to go through the rest of the gears if you're not going to use them to accelerate. Now just use as little throttle as possible to maintain speed. You should keep the RPM as low as possible for cruising. 1-2k is ideal, but not lower than that. Try to leave a large enough gap to the car ahead so that you can just lift off the gas and coast a bit when other cars ahead brake because they are too close to each other. If you need to accelerate again, shift into a lower gear that will put the revs around 2-3k and accelerate quickly, then get back off the gas and into 5th.
Coast whenever possible. If you are approaching a stop sign or red light coast up to the stop in what ever gear you were in. leave your foot completely off the throttle. This allows engine braking. When engine braking the fuel supply is shut off and you are using no fuel at all. If you apply even a tiny amount of throttle the injectors start supplying fuel agin. Shift into neutral as the RPM drops to 1000. This can usually be done w/o the clutch.
If you are a long way from the stop and don't have enough momentum to get there with engine braking shift into neutral and coast. You will be surprised how far your car will roll w/o any throttle. Be aware of cars around you and don't coast at excessivly slow speeds. I like to keep my speed no more than 5mph below the limit unless I'm rolling up to a stop and there is not a car behind me wanting to turn right at the light into a RH lane that I would block him if I'm crawling along.
I consistenly get 23mpg in mixed driving. 25 mpg if I really pay attention and take every opportunity to save fuel.
Once you reach you cruising speed let off the gas and shift into 5th from what ever gear you were in. No need to go through the rest of the gears if you're not going to use them to accelerate. Now just use as little throttle as possible to maintain speed. You should keep the RPM as low as possible for cruising. 1-2k is ideal, but not lower than that. Try to leave a large enough gap to the car ahead so that you can just lift off the gas and coast a bit when other cars ahead brake because they are too close to each other. If you need to accelerate again, shift into a lower gear that will put the revs around 2-3k and accelerate quickly, then get back off the gas and into 5th.
Coast whenever possible. If you are approaching a stop sign or red light coast up to the stop in what ever gear you were in. leave your foot completely off the throttle. This allows engine braking. When engine braking the fuel supply is shut off and you are using no fuel at all. If you apply even a tiny amount of throttle the injectors start supplying fuel agin. Shift into neutral as the RPM drops to 1000. This can usually be done w/o the clutch.
If you are a long way from the stop and don't have enough momentum to get there with engine braking shift into neutral and coast. You will be surprised how far your car will roll w/o any throttle. Be aware of cars around you and don't coast at excessivly slow speeds. I like to keep my speed no more than 5mph below the limit unless I'm rolling up to a stop and there is not a car behind me wanting to turn right at the light into a RH lane that I would block him if I'm crawling along.
I consistenly get 23mpg in mixed driving. 25 mpg if I really pay attention and take every opportunity to save fuel.
06-27-2008, 06:08 AM
#10
Back in the day when the U. of Saskatchewan high mileage team got over 6000 mpg they...
used that techique, i.e. accelerate hard and then coast. Of course the body of their three (bicycle) wheeled 5 hp Briggs and Stratton-engined vehicle was air foil-shaped (in plan view, looking down). This allowed them to actually be propelled by any cross winds while coasting. Something our cars won't do.
Nevertheless, the acceleration-coast technique works. Pain in the ash to be a passenger in or follow a car being driven in that manner but I think it works.
The one thing about neutral and coasting that you could change is going down hill: In neutral, the engine is still being fueled. If you coast down hill, foot off the pedal, IN GEAR (edit), the ECU shuts down the injectors - no fuel is being used.
Just in case you wanted to know.
Nevertheless, the acceleration-coast technique works. Pain in the ash to be a passenger in or follow a car being driven in that manner but I think it works.
The one thing about neutral and coasting that you could change is going down hill: In neutral, the engine is still being fueled. If you coast down hill, foot off the pedal, IN GEAR (edit), the ECU shuts down the injectors - no fuel is being used.
Just in case you wanted to know.