economy_guy
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Fuel Economy Questions

Sat 06 Jun 2009 11:45:32 PM
Hi, I just joined up because I'm thinking about buying a K11 Micra (basically from the point of an ultimate low cost commuter vehicle - I need a new car). To give a bit of background, fuel economy has been an obsession of mine over the last few years.

With the new purchase I'm basically trying to optimize lowest total costs per year.

I'm leaning towards a Micra. I'd consider maybe a Daihatsu Charade Centro as an alternative (or at most a Starlet, the 1998 Prius is a bit too expensive for now for the amount I'd save even in a worst case scenario of more driving and $4/l petrol), but there are several factors that sway me in the direction of the Nissan, notably the timing chain not having to be replaced every few years (as the timing belt would need to be), the engine being bigger would probably last longer. The K11 is reputed to have good build quality and not many issues with regards to maintenance. Also the enthusiast community is far larger, there is a Haynes manual, etc.

I've done my searching the forums to find the answers, but I can't find them so I'm asking here.

1. Does anyone know the drag coefficient of the Micra? I can't find this anywhere. I suspect it would be somewhere between 0.33 and 0.37, but would like to get a more accurate figure.

2. Has anyone here beat the specification highway figure of 4.4l/100km? By what? Any hypermilers here? From browsing the forum few people seem to do better than 6l/100km.

3. What is the lowest rpm @ 100km/hr figure someone here has achieved through changed gearing or larger tyres, and how did they do it? How much did it cost, and were there any downsides? How much did the fuel economy change?

That's basically it. If anyone has any questions on fuel economy or how to improve it (driving or modifications), I'll do my best to answer. It has been my hobby for several years now and my background is engineering.
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Re: Fuel Economy Questions

Sun 07 Jun 2009 12:42:01 AM
For some reason whenever I think about using 'economy driving' in a car with an engine as frugal as the CG13, it just doesn't seem to compute. It just goes against my nature to try and be efficient in a car that is already as efficient as you're going to get for the amount you pay for a car (given how cheap they're going these days).

I can't imagine what would compel someone to consider a '98 Prius, simply because you'd be looking at a grey import, expensive battery replacements, SFA support and the fact that you have to put up with having a Prius.

Personally I'd ignore all of the hype surrounding the issues of having to replace the timing chains in the CG13. You have the right idea in that they're meant to last the life of the engine and if it does break, just spend the $400-500 for a low KM motor and chuck it in. If it's noisy, just keep it going with fresh oil, check the tensioners from time to time and if it breaks, just replace the motor. A bit of noise on startup when warming is nothing to worry about, however.

I don't believe you'll find any 'hypermilers' here, simply because the vast majority of members want to improve performance and honestly don't care about the bit of extra fuel they'll be using, simply because it's negligible anyway (just ask a few of the turbo guys what kinda fuel consumption they're getting..).

You /could/ switch to a different gearbox with taller ratios for 5th (can't remember which would suit, but see here for some info).

If you really want, get a Micra, chuck it on direct gas injection if you can/want and go from there. I don't believe I'll ever understand how you might get enjoyment out of driving economically, but I suspect it's probably the same as how people look at people like us, who do modify their cars to a similar extent.

---dens
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Re: Fuel Economy Questions

Sun 07 Jun 2009 12:55:12 AM
1. No, that's something I haven't found yet.....woulkd be interesting to know though.

2. 4.4l/100km is quite a bit above the factory specification, (the equivelent of 64.2mpg). Perhaps you converted the mpg figure using a US gallon, (~3.78l), instead of a EU gallon, (4.54l)? Factory specs would be closer to 5.4l/100km, which I have managed to achieve from my 1.3 GX, all be it driving at 56mph for most of the trip.

3. You can calculate these by using the gearbox ratios listed on this site;

http://www.micra.com.au/technical-articles/nissan-micra-specifications.php

And by using a calculator such as the one below to plug in wheel and tyre sizes;

http://www.catherineandken.co.uk/sti/tyres.html

Over here in the UK the only way of making a car ultra efficient in terms of cost per mile is to go for an LPG conversion, should one consider it to be worth it in the long run. I have had my 1.3 GX converted with a BRC sequential LPG injection system and it's very cost effective. Slightly less mpg than on petrol but at only 50% of the cost of petrol per litre it's already saving me a lot on fuel costs. Not a car many would convert due to it's street value but it works for me.

Hope this helps :)
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Re: Fuel Economy Questions

Sun 07 Jun 2009 11:41:38 AM

economy_guy WROTE:

"
I'm leaning towards a Micra. I'd consider maybe a Daihatsu Charade Centro as an alternative."


i own a centro and micra atm. i can tell you centro is better on fuel by experience
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Re: Fuel Economy Questions

Sun 07 Jun 2009 12:45:09 PM
Hi Economy Guy,

The k11 micra is officially rated a 6/100km combined... but as everyone knows these offical figures are just a basic guide and rarely reflect real life..
http://www.environment.gov.au/cgi-bin/settlements/transport/fuelguide/fuelguide.pl?querytype=vehicle&vehicleid=3753

I always average somewhere between 6 and 6.5/100Km in "real world" conditions during my daily 80km commute. This generally includes about 85% highway driving (at a steady 100Km/hr) and 15% urban stop-start conditions. I am not a diehard "hypermiler" but i don't push the car hard, i am always light on the throttle etc. My car is at 250,000kms but is regularly serviced, tyre pressures checked etc. so it's in pretty good mechanical shape for it's age.

As economy is also a higher priority for me than performance when commuting these days I am currently planning to buy a new Suzuki Alto when they are released in August... Not fast or sporty (and probably not considered "cool" by most people) but they should be durable, reliable and will be the most fuel effecient petrol car on sale in OZ.
http://www.suzuki.com.au/cars/limitededition.php
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Re: Fuel Economy Questions

Sun 07 Jun 2009 02:48:52 PM
deNs WROTE:

"For some reason whenever I think about using 'economy driving' in a car with an engine as frugal as the CG13, it just doesn't seem to compute. It just goes against my nature to try and be efficient in a car that is already as efficient as you're going to get for the amount you pay for a car (given how cheap they're going these days).

I can't imagine what would compel someone to consider a '98 Prius, simply because you'd be looking at a grey import, expensive battery replacements, SFA support and the fact that you have to put up with having a Prius.

Personally I'd ignore all of the hype surrounding the issues of having to replace the timing chains in the CG13. You have the right idea in that they're meant to last the life of the engine and if it does break, just spend the $400-500 for a low KM motor and chuck it in. If it's noisy, just keep it going with fresh oil, check the tensioners from time to time and if it breaks, just replace the motor. A bit of noise on startup when warming is nothing to worry about, however.

I don't believe you'll find any 'hypermilers' here, simply because the vast majority of members want to improve performance and honestly don't care about the bit of extra fuel they'll be using, simply because it's negligible anyway (just ask a few of the turbo guys what kinda fuel consumption they're getting..).

You /could/ switch to a different gearbox with taller ratios for 5th (can't remember which would suit, but see here for some info).

If you really want, get a Micra, chuck it on direct gas injection if you can/want and go from there. I don't believe I'll ever understand how you might get enjoyment out of driving economically, but I suspect it's probably the same as how people look at people like us, who do modify their cars to a similar extent.

---dens"


So the standard k11 gearbox has .75 5th gear so it will be great for fuel economy, especially on highway driving, i need to get one of those viscous boxes, those ratios are alot better for performance.
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Re: Fuel Economy Questions

Sun 07 Jun 2009 09:14:01 PM
Hi deNs, thanks for the reply.
deNs WROTE:

"For some reason whenever I think about using 'economy driving' in a car with an engine as frugal as the CG13, it just doesn't seem to compute. It just goes against my nature to try and be efficient in a car that is already as efficient as you're going to get for the amount you pay for a car (given how cheap they're going these days).



"

I guess it's just perspective. I used to drive without much care for fuel economy. But now I do it just because I can, and I now get more joy out of saving money and the actual challenge of driving to save fuel. It's as interesting as anything else you can do on a commute, and won't get you a ticket.

I can't imagine what would compel someone to consider a '98 Prius, simply because you'd be looking at a grey import, expensive battery replacements, SFA support and the fact that you have to put up with having a Prius.


"

Several reasons, the ability to "glide" with the engine off, without wearing out either a clutch or a starter motor when you start the engine back up (indeed, the car does it for you). I guess that and the pretty low drag coefficient.

If you really know what you are doing, you can get close to 3l/100km with no modifications to the aerodynamics, and probably a bit better with some grille blocking and a partial undertray. That's motorbike territory. The other plus of hypermiling is lower maintenance costs. Get good enough, you'd never replace your brakes. Your tyres last a lot longer, since they are used less in pushing hard to stop your vehicle (and to maintain a constant torque by pushing the car into excess air resistance). And your engine works less hard per km, because the key is basically:
1) Cutting out the acceleration (and hence fuel used and engine wear and tear) used in avoidable stops, by carefully watching the road ahead, knowing your route and planning accordingly to not accelerate when you know you'll have to brake.
2) Cutting out the excess revolutions the engine is doing by being in too high a gear for the workload.
3) Cutting out the extra revolutions and strain involved in the engine working overly hard pushing against the wind, by not going excessively fast (e.g. sticking to 80kph or below or following a larger vehicle at a safe enough distance behind.)

Note that accelerating more gently than say, 1/3 to 1/2 throttle isn't going to help things, since it's in the above points where the fuel is wasted.

So why do all that? Because of the challenge, and the money saved in fuel and maintenance. How much? Well, if the prius should get 4.5l/100km and you can get 3l/100km, that's 1.5l/100km you are saving. If your commute is 15,000km per year, that's 225l/year. If the fuel prices were $1.80 like they were last year, or if they go higher, that's $400/year. Add in maintenance and you are saving some more. So maybe $500-$600/year. And then depreciation - you should get a few more years out of the same car, so maybe it's more like $800-$900. And the more fuel prices rise, the better off you are compared to other people (and during which times, your money will probably be buying more).

As you rightly suggest, this is just icing on the cake of the thousands you are saving by not owning a large passenger vehicle or an SUV.

Back to the prius - the prius community is also huge. There are plenty of people who have gotten to know (and write about) the "Prius Classic". So I suspect I'd be able to get the car fixed. It's also Toyota, they don't usually make junk. However, if the price doesn't justify it I won't be buying one.

Personally I'd ignore all of the hype surrounding the issues of having to replace the timing chains in the CG13. You have the right idea in that they're meant to last the life of the engine and if it does break, just spend the $400-500 for a low KM motor and chuck it in. If it's noisy, just keep it going with fresh oil, check the tensioners from time to time and if it breaks, just replace the motor. A bit of noise on startup when warming is nothing to worry about, however.


"

Thanks very much for that info!

You /could/ switch to a different gearbox with taller ratios for 5th (can't remember which would suit, but see here for some info).


"

I had a look there, thanks.

If you really want, get a Micra, chuck it on direct gas injection if you can/want and go from there. I don't believe I'll ever understand how you might get enjoyment out of driving economically, but I suspect it's probably the same as how people look at people like us, who do modify their cars to a similar extent.



---dens"

I've modified cars for performance before, so I understand their motivation. Having a family changes a person's priorities though. I'm a bit dubious about putting it on gas because I'm not sure about maintenance issues and if it would pay for itself. Also if/when there is another fuel crisis I would expect gas to start costing what it can produce in energy (much like Diesel shot up), when it starts getting shipped around the world.
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Re: Fuel Economy Questions

Sun 07 Jun 2009 09:49:24 PM
best i've done is 4.7... 730km+ with atleast 4-5l left in the tank, and from memory, I kept the revs around 3000+ rpm (which flies in the face of conventional wisdom of low revs... its all about torque for the micra). I have a 120km daily trip 1/2 hiway 1/2 mountain range..... standard rims and tyres, light flywheel, I think thats as close as the best you'll get in a micra, unless you ditch the engine completely and go bev then is 10c a km then that's a different story altogether.
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Re: Fuel Economy Questions

Sun 07 Jun 2009 09:57:25 PM
SSUK WROTE:
2. 4.4l/100km is quite a bit above the factory specification, (the equivelent of 64.2mpg). Perhaps you converted the mpg figure using a US gallon, (~3.78l), instead of a EU gallon, (4.54l)? Factory specs would be closer to 5.4l/100km, which I have managed to achieve from my 1.3 GX, all be it driving at 56mph for most of the trip.





...Over here in the UK the only way of making a car ultra efficient in terms of cost per mile is to go for an LPG conversion, should one consider it to be worth it in the long run. I have had my 1.3 GX converted with a BRC sequential LPG injection system and it's very cost effective. Slightly less mpg than on petrol but at only 50% of the cost of petrol per litre it's already saving me a lot on fuel costs. Not a car many would convert due to it's street value but it works for me.



Hope this helps :)"

Thanks for the help. A fair few sites list the Micra as being able to get 4.4l/100km on the highway. Notably carbuddy and environment.gov.au. Perhaps they made an error?
http://www.carbuddy.com.au/car/values/specification/default.aspx?mk=NISSAN&md=MICRA&y=1995
http://www.environment.gov.au/settlements/transport/fuelguide/search.html

But then again, technology wise, a good comparison is probably the toyota starlet that supposedly gets 4.8l/100km. Similar engines (same number of valves, both not VVT, same approx size). However, the Toyota has slightly more frontal area, a slightly bigger engine, slightly more weight. All this points to a slightly worse fuel economy, which is what the figures indicate.

So unless something is amiss (e.g. maybe Micra has higher Cd), the Micra figures don't look too out of the ordinary.

However, 5.6l/100km is a good start, at roughly 90kph. Thanks for the info.
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Re: Fuel Economy Questions

Sun 07 Jun 2009 10:01:19 PM
eeden WROTE:
i own a centro and micra atm. i can tell you centro is better on fuel by experience

"

Cool. I'll keep that in mind. Any figures?

Edit: I can think of a few factors that could cause the real world difference. For one, the 20% increase in kerb weight for the micra. If someone is driving "normally" (without attempting to eliminate all possible stops), this will result in 20% worse fuel economy. However, this should show up in the city fuel economy figures but they are identical.

The other factor is the much smaller engine in the Centro. If the Centro is like the other 660cc daihatsus, they use about 4000rpm at 100kph in 5th gear. This means they get significantly worse fuel economy at higher speeds than they otherwise should because of the gearing. Since not all driving is done at highway speeds, the Centro should again be better in stop and go I would think.
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Re: Fuel Economy Questions

Sun 07 Jun 2009 10:19:19 PM
fred WROTE:

"best i've done is 4.7... 730km+ with atleast 4-5l left in the tank, and from memory, I kept the revs around 3000+ rpm (which flies in the face of conventional wisdom of low revs... its all about torque for the micra). I have a 120km daily trip 1/2 hiway 1/2 mountain range..... standard rims and tyres, light flywheel, I think thats as close as the best you'll get in a micra, unless you ditch the engine completely and go bev then is 10c a km then that's a different story altogether. "

Did you get the 4.7 on the 1/2 mountain range commute? Without doing anything special, for example, putting the car in neutral going down the hills, or getting to near the crest of a hill and timing the stop of your acceleration so that you are going significantly slower than the speed limit on the crest, to both prevent having to brake to stay within the speed limit or going excessively fast and turning kinetic energy into wind behind the car (and eventually heat)?

Generally, you can achieve better fuel economy on a hilly route than flat if you know what you are doing. This is because going up the hills you can use the engine at a throttle where it is producing more kinetic + gravitational potential energy for the fuel (e.g. lower Brake Specific Fuel Consumption, BSFC). On the downslope you can stick it in neutral (even turning the engine off) without other cars really noticing much. And yeah, I know that you can also feather the engine so that the injectors turn off. However, the pumping losses in converting the car's kinetic energy to heat by having the car in gear are more than the small amount of fuel used in idling the engine.

(In a similar way that there is more scope for doing better with city driving than highway driving in general - if you can turn your engine off at the stops, and drive in such a way that you are anticipating the many obvious stop lights and stopped cars, the engine is in a better rpm range for fuel economy and the speeds are great for lowered air resistance.)
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Re: Fuel Economy Questions

Sun 07 Jun 2009 10:20:27 PM
economy_guy WROTE:
I'm a bit dubious about putting it on gas because I'm not sure about maintenance issues and if it would pay for itself. "


i,ve encountered no maintenance issues from 2yrs (34k miles) of use on this car and 4yrs of use in my old super s, it has saved me thousands, lpg ftw :)

frank
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Re: Fuel Economy Questions

Mon 08 Jun 2009 08:44:05 PM
round trip included mountains.... I was wondering if you've thought of making a billy cart, they're great down hills and depending what you had for lunch and your fitness level are pretty easy on the hills......
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Re: Fuel Economy Questions

Mon 08 Jun 2009 11:56:59 PM
hmmm.. I wouldn't touch a prius with a ten foot pole.. I've complied atleast 20 of em now... They constantly have battery trouble etc.. And I get better fuel economy out of my turbo red car (130kw @ wheels) then my daily blue Micra LOL. Around 600-620 for the turbo, and 550ish for the daily. Don't really drive either with fuel economy in mind... Doesn't seem to effect fuel consumption no matter how I drive LOL .
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Re: Fuel Economy Questions

Tue 09 Jun 2009 01:25:10 AM
economy guy, you could fit some 1.0 pistons to get a 12:1 compression ratio then advance the inlet cam, which would give a similar (atkinson cycle-esque) spec to the prius engine ;)

frank
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Re: Fuel Economy Questions

Wed 10 Jun 2009 02:52:10 PM
I have my CVT automatic micra as a dual fuel setup.

On LPG I get 8.8 +/- 0.5 L/100km most of the time.

On Petrol I was getting about 6.7 +/- 0.5 L/100km most of the time.

With LPG at 45c/L and Petrol at 115c/L

Thats:

LPG -- $4/100km

Petrol -- $7.70/100km

So about petrol works out to be nearly twice the price/km

Based on 20,000km/year that's a saving of $800/year.

Even if the LPG price increases, it is unlikely to increase more quickly than Petrol at such a rate so as to be 80% of the cost of petrol anytime soon (in the capital cities). In the bush its a different story because of increased transport costs.

Do the calcualtions for yourself, if you don't mind having a totally different set of fuel efficiency numbers to most.

P.S. This is cheaper/km than most prius drivers (1.15*4 = $4.60/100km if they are lucky.) would get at the moment, and costs a lot less to set up.

P.P.S. If it was a manual you could assume about a 25% increase in fuel efficiency. Thus a cost of about $3/100km.
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Re: Fuel Economy Questions

Wed 10 Jun 2009 03:05:21 PM
One thing my friend and I tried was to use a copper pipe to allow the collant to bipass the manifold, where the pressure of the collant appears to be used to tell the ECU information.

This appears to have resulted in an increase in fuel efficiency of about 3%. However, otherthings were done at the same time. These include.

1. Removing part of the front grill under the left hand headlight to allow cold air to flow more freely into the intake.

2. Covering up some apparently factory built holes in the intake. Does anybody know their purpose?

This resulted as I said in improved economy figures. However, the engine tended to idle high once warm due to the aforementioned ECU connection. This resulted in large clunking noises from the transmission (I assume) when it appeared to engage or disengage.

This problem appeared worse on colder days, and as winter has arrived it was quite bad leading me to reinstall it as before.

If you lived in a more temperate zone this may be an option for you.

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Re: Fuel Economy Questions

Wed 10 Jun 2009 03:14:07 PM
Does anybody know if painting the air intake and box white instead of black would improve the efficiency? I assume they made them black to absorb heat so that you don't get freezing of water vapour in europe. Not really releavant in Aus most of the time.

I figure that black absorbs better in the infra-red (IR) range as it does throughout the visible range and there would most definitely be a lot of IR going around in the engine bay.
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Re: Fuel Economy Questions

Wed 10 Jun 2009 05:19:54 PM
david WROTE:

"Does anybody know if painting the air intake and box white instead of black would improve the efficiency? I assume they made them black to absorb heat so that you don't get freezing of water vapour in europe. Not really releavant in Aus most of the time."


If not in direct sunlight, I would have thought that the materials used would have more of an effect on the insulation properties of the airbox (i.e. an metal airbox as compared to a plastic one) rather than if it were painted or not, since the plastic isn't painted. Don't ask me whether metal or plastic airboxes are better though :P

---dens
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Re: Fuel Economy Questions

Fri 12 Jun 2009 10:55:15 PM
david WROTE:
1. Removing part of the front grill under the left hand headlight to allow cold air to flow more freely into the intake.
"

In my experience (and that of others) typically the done thing to improve fuel economy with intake air is to make it warmer (blocking the grille, routing it from the engine bay rather than the outside).

The reason why that works is that with petrol cars (as opposed to diesel) you have a throttle plate that gets closer to closed at idle. This is not efficient - it is like trying to breathe through a straw.

When you warm the air (using the engine's waste heat), the air gets less dense, meaning less air molecules will fit in the combustion chamber for a given throttle opening. That means that to get the same power you need to open the throttle more, making it more efficient. Of course if you are after higher peak power this will not help.

If you cool the air you get higher peak power but worse fuel economy.
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Re: Fuel Economy Questions

Fri 12 Jun 2009 11:23:16 PM
frank2 WROTE:

"economy guy, you could fit some 1.0 pistons to get a 12:1 compression ratio then retard the inlet cam, which would give a similar (atkinson cycle-esque) spec to the prius engine ;)



frank"

That's interesting. I haven't really got into hacking into engine internals yet. Do you think it would work, and how hard and expensive do you think it would be?
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Re: Fuel Economy Questions

Fri 12 Jun 2009 11:23:52 PM
if you get higher power, you increase efficiency.... better fuel econ.... your logic is fading
economy_guy
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Re: Fuel Economy Questions

Fri 12 Jun 2009 11:59:38 PM
fred WROTE:

"if you get higher power, you increase efficiency.... better fuel econ.... your logic is fading"

It's not that simple. Power is the output. Litres of petrol per unit time is the input. All else being equal, in any engine the amount of fuel used to produce a given amount of energy (per unit time) depends on throttle and rpm. This is mapped on a BSFC curve. BFSC is Brake Specific Fuel Consumption, or how much fuel required to produce a given amount of energy (per unit time).



The above BSFC graph is that of a typical petrol engine. It is a topographical map, where the bottom of the valley (the bubble in the upper left) represents the most fuel efficient range the engine can operate. Note that it occurs at about 2500 rpm, at 3/4 of the total power that the engine could produce at that rpm.

Unfortunately, to design a commercially acceptable car means that you need an engine big enough to accelerate capably. However, most driving is not accelerating, it is steady cruising. This needs way less power. On the BSFC map, steady cruising would be low rpm and low power (lower left on the graph), and note how far away we are from the lowest BSFC.

If you don't mind accelerating more slowly, you can sacrifice peak power for fuel economy, by getting an engine that is sized closer to the power required to cruise. (This is the postie bike approach - 1l/100km). A warm air intake is a way to do the same thing. Note that since most driving is steady cruising, a slower acceleration does not appreciably change the commute time.

You could also familiarize yourself with the following:

http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

Another thing that will become obvious with study of the BSFC map - accelerating moderately hard (not at WOT, although that is not particularly inefficient) is actually efficient. The problem is not the acceleration, it is the lack of planning for obvious stops (e.g. impending red lights, stopped traffic, exit ramps, beginning the descent on a big hill, etc.).
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Re: Fuel Economy Questions

Sat 13 Jun 2009 12:07:03 AM
david WROTE:

"Does anybody know if painting the air intake and box white instead of black would improve the efficiency? I assume they made them black to absorb heat so that you don't get freezing of water vapour in europe. Not really releavant in Aus most of the time."

I don't think it matters. My belief is that they are black like most of the other plastic engine parts because they don't show oil stains. If you want to be ultra, ultra pedantic, black will help because it will absorb IR and help heat up the intake air (assuming it is colder than the engine bay).
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Re: Fuel Economy Questions

Sat 13 Jun 2009 01:04:02 AM
bmw has showed that slow acceleration is bad for fuel economy...


only 10 min of my driving is steady state, and yes i mind if i slowly accel...adds 10mins to a journey over 65km and in the end we're talking about $1.50 over a tank of fuel... I get my coffee for free so my bank balance doesn't care, why are you preaching so hard? and of course its simple, raise your efficiency and you raise economy...wonder why all oem are going turbo? they can use smaller motors for the same power but with higher economy.......
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Re: Fuel Economy Questions

Sat 13 Jun 2009 01:41:33 AM
economy_guy WROTE:

"
david WROTE:
1. Removing part of the front grill under the left hand headlight to allow cold air to flow more freely into the intake.
"

In my experience (and that of others) typically the done thing to improve fuel economy with intake air is to make it warmer (blocking the grille, routing it from the engine bay rather than the outside).

The reason why that works is that with petrol cars (as opposed to diesel) you have a throttle plate that gets closer to closed at idle. This is not efficient - it is like trying to breathe through a straw.

When you warm the air (using the engine's waste heat), the air gets less dense, meaning less air molecules will fit in the combustion chamber for a given throttle opening. That means that to get the same power you need to open the throttle more, making it more efficient. Of course if you are after higher peak power this will not help.

If you cool the air you get higher peak power but worse fuel economy."


Forgive my ignorance, but I thought if the throttle is more open it sends more fuel in to get the same rpm with the hot/warm air. Do you have more information to support the warm air intake to increase fuel economy stance.

Everything else I have read has said cold air intake increases both power and efficiency.
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Re: Fuel Economy Questions

Sat 13 Jun 2009 07:27:35 AM
economy_guy WROTE:


That's interesting. I haven't really got into hacking into engine internals yet. Do you think it would work, and how hard and expensive do you think it would be?"


yeh, sure, i,ve got some (leftover) 1.0 (flatop) pistons fitted to some 1.3 rods, ready to install, the (80) 275deg inlet cam is already fitted and is easily retarded, so little in the way of cost, but you would have a serious lack of low down grunt tho :o

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Re: Fuel Economy Questions

Sun 14 Jun 2009 03:40:28 PM
sounds boring.

much more fun thrashing.

micras use stull all fuel thrashing too. win!

I tell ya though this Golf GTI 2.0L TFSI uses a fair bit of fuel when you kick it in the guts. :( Not uncommon to see it reading up around 30L/100km when having a little bit of legal fun on a twisty road. Flat out the computer reckons its using upwards of 40L/100km and I would believe it as I can see all the expensive PULP on the tailgate. Yes it can be driven very economically but the computer pipes up and tells you that you're a poofter so to teach it a lesson you dent the firewall with the go pedal and then fun happens. I am able to keep it down around 8L/100km in normal driving though by letting the computer do all the thinking for me and being gentle.
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Re: Fuel Economy Questions

Sun 14 Jun 2009 10:57:33 PM
david WROTE:
Forgive my ignorance, but I thought if the throttle is more open it sends more fuel in to get the same rpm with the hot/warm air. Do you have more information to support the warm air intake to increase fuel economy stance.



Everything else I have read has said cold air intake increases both power and efficiency."

Cold air certainly increases power. Efficiency, only at Wide Open Throttle (WOT).

Here is a quote I pulled from gassavers.org that explains it pretty well, except they have it around the wrong way - for any given mass of oxygen, a corresponding amount of fuel is injected:
2) With oxygen sensors, engines run at stoichiometric air/fuel ratios. For any given amount of fuel, a corresponding mass of oxygen is admitted. WAI lowers the density of air, meaning that a higher volume of air must be let into the engine for a given fuel input. So with WAI, the throttle must be opened further for a given output, and this lowers the "pumping" work of pulling air past the throttle."


So what happens is that in order to cruise at a given speed (all else being equal), you need a certain amount of power. To generate this power with warm intake air as opposed to cold, you need the throttle open wider because the air is less dense, to get approximately the same number of air molecules for the amount of fuel to generate that power.

But, because the throttle is cracked open more, there are less pumping losses, meaning you generate a little more power (and hence why I said "approximately", because to generate the same power you will need slightly less air molecules and slightly less fuel, but the throttle is still cracked open more than the cold air intake. Whew!

Some links:
http://www.techno-fandom.org/~hobbit/cars/heatgames/pagethree.html
http://www.gassavers.org/archive/index.php/How-to-build-your-own-Warm-Air-Intake-WAI/t-244.html
http://ecomodder.com/forum/showthread.php/warm-air-intake-how-warm-can-you-go-8140.html
http://www.metrompg.com/posts/wai-test.htm
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Re: Fuel Economy Questions

Mon 15 Jun 2009 11:17:29 AM
I have a 1L K11 5spd, never managed better than 43mpg (6.57 L/100km), mostly about 39mpg (7.24L/100km), I've another friend who gets similar. I run with over inflated tyres and when fuel prices were high I'd shut off the engine & coast in neutral down hill or when approaching traffic lights.
Friends 1L & 1.3L K11 regularly get 48mpg (5.89 L/100km) without going to any of the above extremes. I've checked everything I can think off (O2 sensor, MAF, wheel alignment...), I don't know why I can't get better mileage.

EVLGTI now owns a 1998 Caldina 5spd weighing 1200kg with the 1.8L 7A-FE leanburn motor. He's getting 48mpg (5.89 L/100km) just driving normally, through traffic to work and around hilly auckland.

Personally I think the fuel economy from lean burn engines made in the 90's will be hard to improve upon. Around 2000 emmissions regulations changed and these motors were no longer produced.
Early 90's Honda Civic SOHC VTEC-E version with leanburn D15.
Later 90's Honda Civic VTI with leanburn 3 stage VTEC D15.
1994 on Toyota Carina with leanburn versions of the 1.6L 4A-FE or 1.8L 7A-FE
1996 on Toyota Corona, Premio, Caldina with either of the above motors.
1998 on Nissan leanburn 1.8L QG18DE in various vehicles.

Depreciation is usually one of the larger costs in operating a vehicle, 90's vehicles have already depreciated significantly.

I don't think as much effort is put into reducing fuel consumption in small cars, just cost. 660cc cars are just small, lightweight & built cheap. If you've got your mind set on small, perhaps Toyota Iq might be a better long term prospect?

I don't think much of prius, too heavy, & batteries are too expensive
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Re: Fuel Economy Questions

Mon 15 Jun 2009 02:33:40 PM
nz_aj WROTE:

"I have a 1L K11 5spd, never managed better than 43mpg (6.57 L/100km), mostly about 39mpg (7.24L/100km), I've another friend who gets similar. I run with over inflated tyres and when fuel prices were high I'd shut off the engine & coast in neutral down hill or when approaching traffic lights.

...
Depreciation is usually one of the larger costs in operating a vehicle, 90's vehicles have already depreciated significantly.



I don't think as much effort is put into reducing fuel consumption in small cars, just cost. 660cc cars are just small, lightweight & built cheap. If you've got your mind set on small, perhaps Toyota Iq might be a better long term prospect?



I don't think much of prius, too heavy, & batteries are too expensive"

Well, it looks like I'll be getting a Micra, put the deposit on it today. I'll see what I can do with it over a full tank. I've got a good amount of experience hypermiling, so it will be interesting to see what I can do. I suspect I'll be able to beat the 4.4l/100km figure, and do better if I modify the car a bit. I only hope I don't get called a liar. :)

I do all the stuff you mentioned too, the engine off coasting etc. Do you also do your best to time it so that by the time you hit the lights you don't have to brake at all? It has to be either driving technique or something wrong with the car if an identical car is doing better. Another possibility - is your car modified at all? The original Micra wheel covers are about as good as you can get for fuel economy (unless you were to replace them with pizza trays). If you have mags (or fatter tyres), that could be part of the problem.

The car necessary for fuel economy depends a lot on how you drive it. If you can avoid all unnecessary stopping (and most of it is avoidable), weight is a small to moderately important variable. Weight will matter somewhat, but more important is low drag coefficient * frontal area (CdA). Engine size is also important. It would be interesting to experiment with a Calibra, but I favour the lower purchase price of the Micra. As far as lean burn engines go, they are nice, but if the only time you have the engine in gear it is accelerating near best BSFC, otherwise it is in neutral, you don't need lean burn since lean burn only increases efficiency when the engine is doing little work.

If a person can't be bothered to avoid unnecessary stops or finds it too difficult, weight will be a very important factor and outweigh most other considerations.

If a person is addicted to driving fast and doesn't draft behind large vehicles, then Cd*A and high gearing are important things to look for.

As far as depreciation, that's an important cost to consider. I made up a spreadsheet to calculate the yearly cost of different cars, with a best case and a worse case (e.g. of fuel economy). If anyone can let me know how people normally upload files here, I can upload it and let other people play with it if they want. Suffice to say, based on my calculations I think the Micra is the best deal I can find at the moment, as far as covered (i.e. non-motorcycle) transport, in terms of cost per year combined with low purchase price.

I think you'll find with something newish, the depreciation will tend to blow out the cost. It's hard to compete with ~$4k, ~5l/100km, when the cost is $10,000+. The other thing is that if you find a well maintained car that is known for reliability and change the oil and coolant regularly, drive it sedately etc., it will probably run a long, long time. This reduces depreciation cost as you can run the car more years.

Another thing to consider is the interest cost. If you are buying a more expensive car, you have to consider what it is costing to do so, either the cost of the interest or the opportunity cost of the money you could have used to invest with.

Put simply, I don't think the Micra's combination of reliability, fuel economy and low purchase price can really be beaten at the moment. The only downside is safety, which is something common to all cars and means that you need to learn to drive very defensively. But that can be learned.
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Re: Fuel Economy Questions

Mon 15 Jun 2009 05:02:08 PM
oh wow this topic hurts my brain, i get the hypermiling thing, (hyperkilometreing?) but at what expense?

if saving money/the planet really bothers you get a bike, or even a small capacity motorbike

enthusiasts buy micras because they are fun, and cheap (not in turbos case)


so forget all this theory and buy one, you won't be dissapointed (for a while)

put some good suspension bits in it so you can take your engine off downhill corners properly, put some decent brakes on it then revel in the glory that you can enjoy the twilight years of the cheap oil age guilt free in your frugal little 1.3l car


PS: engine off coasting is dangerous, unless you have some fancy way of making your brakes work properly

PPS: yom you are a funny bastard "Yes it can be driven very economically but the computer pipes up and tells you that you're a poofter so to teach it a lesson you dent the firewall with the go pedal and then fun happens" HAHAHA!

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Re: Fuel Economy Questions

Mon 15 Jun 2009 07:49:05 PM
smidge WROTE:

"oh wow this topic hurts my brain, i get the hypermiling thing, (hyperkilometreing?) but at what expense?



if saving money/the planet really bothers you get a bike, or even a small capacity motorbike

"

I guess I just enjoy it (and not getting wet in the rain with a postie bike)? My commute is a bit large for me to not want to use the freeway. Ultimately there is probably no more point than building a dyno queen, or a quarter mile drag car, or a rally car. Horses for courses.
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Re: Fuel Economy Questions

Tue 16 Jun 2009 07:11:32 AM
There's enough vacuum stored to assist with a couple of applications of the brakes. The whole point is to avoid using the brakes. It's not really a problem.

Yes I'm running the original biscuit steel wheels & standard biscuit width tyres. They're inflated to maximum rated pressure during summer & 110% during winter.

Yes I think there is something wrong with my car. I can't work out what it is & randomly replacing potential parts is too expensive.
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Re: Fuel Economy Questions

Wed 17 Jun 2009 04:36:19 PM
nz_aj WROTE:
Yes I think there is something wrong with my car. I can't work out what it is & randomly replacing potential parts is too expensive."

Hmmm... I wonder... I've driven a Nissan Pulsar before. I know that when you turn off the engine, neither the speed or the odometer register anything. Maybe you are getting the increase in fuel economy but not getting the engine off km?
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Re: Fuel Economy Questions

Thu 18 Jun 2009 02:02:03 AM
I don't believe any of those sites which quote the CG13DE powered cars as being able to do 4.4L/100km at 100kph. None of those figures match the Nissan brochure figures, or come close to realistic driving conditions. For example a SuperS will not do the same fuel economy as an LX model. The SuperS has slightly more frontal area and runs on 175 tyres instead of 155 tyres, so will have more rolling resistance. Having owned a 1.0LX, 1.3GX and 1.3SuperS, this is something which is noticeable.

As for hypermiling, I would actually bring down fuel savings to defensive driving. Anyone who drives to the extremes with severely over inflated tyres, tailgates/drafts large vehicles and drives with the engine off is not driving safely. My life is worth a lot more than the 30/month saving it 'could bring', besides I already save much more by running on LPG without any change in my driving style.

I would like to see someone beat 4.4l/100km, personally without being dangerous I don't see it happening......but one can always try.

A small note though, us peeps from the UK will probably have lower figures anyway due to our congested roads, which don't stretch for miles on end, and as for driving in London......forget it, traffic lights are seen like every 1/2mile hah!
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Re: Fuel Economy Questions

Sat 20 Jun 2009 01:50:02 AM
I would be interested to see what you can get 'economy guy'.
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Re: Fuel Economy Questions

Sat 20 Jun 2009 07:48:44 PM
centro is good with stop and go, you really wonldnt want to take it on the freeway for a long period anyway.

best i am able to get is 4.2/L on highway with the MICRA
thats with no rear seats
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Re: Fuel Economy Questions

Mon 22 Jun 2009 11:10:48 PM
eeden, thanks for the info.

Well, I am now the proud owner of a Micra, so I'll let people know what I get in a week. I hope I filled it up properly, I think I did. It was on empty and I put 33 litres into it.

Some comments: it drives like a sports car! The thing just sits. And when you plant the foot it goes. It's a lot like an original mini I had a drive of once. Very fun. It's hard to be staid with this car, it kind of begs to take the corners a bit too fast etc.

I want it to last a long time, learn to do all my own maintenance etc. So I'll drive it gently. But it does yearn to go fast!

Every woman who looks at the car says that "it's cute!". Ah well. Little do they understand that it is probably the most inexpensive car to own in Australia (considering fuel, interest cost, depreciation, maintenance), and that's why I bought it. It's also fun to drive, which is cool. I can understand why there is a good sized user community around them.
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Re: Fuel Economy Questions

Wed 24 Jun 2009 12:11:04 AM
economy_guy WROTE:

"it drives like a sports car! The thing just sits. And when you plant the foot it goes. It's a lot like an original mini I had a drive of once. Very fun. It's hard to be staid with this car, it kind of begs to take the corners a bit too fast etc.


[snip]

it does yearn to go fast!

"


I chuckled when I read that ;) Enjoy your K11 mate.. they're great fun and I hope you do get decent fuel economy in the end.. especially after all this!

Max I think i've ever filled up with was 35 litres from memory. I've never run it completely dry, but as you've probably already found out from needing ~33L on that fillup, you've still got a fair bit of distance left in it when the fuel light comes on. It's meant to indicate when there's roughly 5L of fuel left in the tank.

---dens
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Re: Fuel Economy Questions

Sun 28 Jun 2009 08:22:55 PM
My K11 has a speedo cable, so the odometer keeps turning over when ignition is off.
Most N14 & newer Pulsars have electronic speedo & odometer, rather than the traditional speedo cable, hence your experience.
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Re: Fuel Economy Questions

Mon 29 Jun 2009 11:17:46 PM
Well, I have my first fuel economy figure. 5.2l/100km over 515km. That's about 80% highway (mostly around 100km/h, some 80km/h), although it seems like it's more in the city because that part can take a long time. I'm a bit bummed I can't get the 4.4 (or better), so it looks like the website I'm basing this off has the wrong info (or Nissan told a porky).

My next tank may be better, because I have just had my wheels balanced and a wheel alignment because the front end was vibrating a bit around 100km/h. I didn't go to empty this time because I wanted to see the difference a wheel alignment/balance can make and compare.

Thanks for everyone who has contributed!
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Re: Fuel Economy Questions

Mon 29 Jun 2009 11:57:05 PM
that sounds about right economy_guy, now fit a 275deg inlet cam like mine, then advance it (to assimilate an atkinson cycle)
and my lpg a/f/r,s go into leanburn at low throttle openings too now :)

frank
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Re: Fuel Economy Questions

Sun 02 Aug 2009 06:12:56 PM
Ok, I have some more numbers.

Tank 2: 4.83l/100km
Tank 3: For some reason when I clicked the odometer it caught and I didn't realize it hadn't advanced from zero until too late into the tank.
Tank 4: 4.98 l/100km

I'm now driving 80-90km/h on the highway, depending on my mood. Sometimes 100km/h, but not too often. The improvement would be that and the wheel alignment/balance.
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Re: Fuel Economy Questions

Fri 25 Sep 2009 04:26:13 AM
My first tank in my super S returnd 6.6L/100ks, a good mix of all round driving, first 300ks of the tank it had a dodgy thermostat making it run cold so I should see an improvement.


it's getting some 14x5.5" rims with 185/60 tyres on the weekend though so that may bite into my economy.
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Re: Fuel Economy Questions

Fri 25 Sep 2009 05:21:56 AM
I get between 6.1 and 6.3L/100kms from my 1275 K11 driving in the hilly pennines of England, that includes brisk driving over some of the best roads in the UK. No chance of me beating any records.
This evening I got a friendly wave from a 5-series BMW driver that had struggled to stay in touch over the Snake Pass, he passed me near the summit due to me not wanting to dent my economy too much on the steepening incline.
I run some hefty 7kg 14x6" alloys with 185/55 tyres too. CD of the K11 is 0.35.