TeamSwift

bi-directional averaged runs (to cancel effects of grade/wind) on my nearly level "test course" that runs sw/ne.

Conditions as of (3:00 pm EDT) on 05/03/2006:

Wind Direction (WDIR): NNE ( 30 deg true )
Wind Speed (WSPD): 3 kts
Wind Gust (GST): 4 kts
Atmospheric Pressure (PRES): 29.94 in
Air Temperature (ATMP): 58.8 °F (this temp. avg'd with another land-based station)

raw data fyi:

km/h - W mpg - E mpg
55 ... 83.1 ... 82.4
60 ... 77.8 ... 76.3
65 ... 74.1 ... 71.7
70 ... 71.2 ... 70.8
75 ... 67.2 ... 62.7
80 ... 63.3 ... 59.3
85 ... 59.4 ... 56.4
90 ... 55.4 ... 53.9
95 ... 51.5 ... 50.3
100 ... 46.6 ... 46.9
105 ... 44.9 ... 44.0

fyi, this is with the following "mods":
- grille block, wheel skirts, smooth wheel covers, tires @ 48 psi

thats interesting date... but i wonder how did you get 82 mpg @ 60 kph

i think 49 mpg on highway is pretty good ( distance vs time vs mpg)

didn't do anything special. level road, cruise control set at 60.

though i have to say i don't like cruising the car below 65 in 5th. i just did 55 & 60 km/h out of curiousity.

I'm surprised more people haven't commented on your data. I'm glad to see someone took the time and had the equipment available to produce this kind of information. I'm pretty sure the scangauge will give you injector pulse width, but will it give you info on air flow? if you could get g/sec of air flow, injector pulse width, a/f ratio at different speeds, combined with the known weight, Cd and frontal area, you'd probably be able to come up with a chart showing exactly how much power the car is producing to maintain certain speeds. It would be great if you could log all of the paramenters, I guess thats where something like Megasquirt would be a big help.

Have you done any comparisons at speed (100+kmh) with windows up vs. down? I'd like to know how big of a difference it makes at 60mph on our cars.

hey mosier -



yeah, maybe people think it's the old thread about rpm vs mpg.



unfortunately, scangauge doesn't give either of those. it doesn't log either. for that level of detail, you need to go to a laptop-based OBD tool.

but couldn't you figure out power output based on the mpg figures?



no i haven't. i wonder too sometimes, especially since the mk 4/5 cars (95+) don't have a windshield gutter on the A-pillar. so i'm thinking the airflow around the pillar would be relatively clean (compared to a car with a gutter), so opening the windows would have a bigger effect since it would be ruining a "cleaner" flow. just a thought.

It looks to me that 46 MPH is where the best efficiency is. I didn't do any math or anything. I just eye-balled it.

That is obtain by getting the largest area under the curve possible. For example..... find any area on the curve, then multiply the x and y coordinates to find the area. The coordinate on the curve that produces the larges area under the curve is also the place that produces the best efficiency.

I don't think that chart is labeled right. I'll write more later.

--------> The dark green line represents gallons/hour because the miles get's canceled out from the top and botton.

Also, the top of your graph should say "MPG vs MPH." That's the way my college displays graphs. The independant variable is usually last. Time is your independant variable which is correctly displayed on the bottom but your title displays it first. I know...I'm being picky, just letting you know.

I think it's cool data though!!! It displays exactly what our beliefs about driving are... if you take your time, you'll save gas. It also shows that this car is more efficient when driving around 50 MPH. Which is expected from most vehicles.

I don't understand why people's driving habit's haven't changed with the higher gas prices. I don't understand why people accelerate hard towards a red light!! They beat me off the line with their big SUV and V8 power, but then I slowly approach them and coast past them at the intersections. My goal is not slow down. So I may drive slow at times, but my average speed is faster. All I have to do is anticipate the traffic and chose the correct lane so I don't have to stop.

I've been trying hard to drive with the most efficiency. I'll shift into 5th gear when I'm at 40MPH. With my Nissan pickup, I get about 26 MPH which is above the EPA estimate, but I'm trying to calculate it again with slower speeds, by shifting into 5th gear sooner, by preventing slowing, and coasting to red lights. Where I live, there are long lines during rush hour just to get through a stop sign. So why rush just to wait?

I guess I'm more patient than other drivers plus I'm a little bored with driving and want to try something new.

Of course we all know the government wouldn't lie.....

Here's some data
http://www.fueleconomy.gov/feg/driveHabits.shtml

The difference between this graph and yours, is the "5th gear." Your graph shows that we should switch into 5th gear faster to save gas. However the highest fuel economy is still maintained when driving around 50 MPH in both graphs.

Hey I saw your website too.
http://www.metrompg.com/posts/60.9-mpg- ... asting.htm
Thanks for the tips!

It does seem hard to believe, but I believe it because the rest of the graph is expected. Plus you have to remember he's driving in 5th gear at a slow constant speed of 60 kph. Just remember the better fuel economy is obtained at 50MPH (75kph). I'll explain....

The big picture is difficult to see in the graph. He is getting 82mpg, but he's driving slow. He has to drive for a longer time to get the same destination or distance. By the time he gets to his desination, he used more gas than if he would have driven at 50 MPH. That's the key. For better fuel economy he's better off driving at 50, not 36MPH.

Ok I'll shut up now.

The graph is right as it is, it isn't showing gallons/hour.

Another thing to remember is that miles per gallon by itself has no relation to time. Driving at 30mph to obtain 80mpg will allow you to drive 80 miles on one gallon. It will take almost three hours to drive those 80 miles, but it can not consume more fuel than driving at 50 with a lower mpg figure and less time. If you want to argue time vs cost or fuel efficiency, then yeah, there will be an optimum speed to drive to balance efficiency and time sitting in the driver's seat.

The nice thing about the graph is how well it shows the cost of increased speed.

It simply takes ALOT more energy to whack those billions of air molecules outta the way at increasing speeds.
Isn't nature wonderful!

It's not just the aerodynamic drag produced by the speeds, but also rolling resistance and engine RPM. At one end of the graph the engine is turning less than 2000, while at the other, its turning over 3000. geometro had talked about changing transmissions at one point, it would be nice to see this same chart with a 4.10 differential, compared to the 4.39.

this is a nice thread. I thought it was the old one. Interesting.

Ah haaa! I knew someone would bite on that.

Ok here's the deal. I really don't want to get into another "flywheel" discussion, but I gotta tell you I've had a lot of Math education. This is a textbook chart that I've learned about in economics and calculus.

Look at the area under the curve (in red). Compare the sizes of the red boxes. Which one is bigger? That's the one that will give you your best fuel economy.





Hey I'm really not trying to be an ass. In fact I like your way of thinking. I like the fact that you were willing to think about it at all!

The EPA is correct. Better fuel efficiency is obtained when driving approximately 50MPH.

I'm not going to start comparing courses here, but I still believe your area under the curve does not represent fuel efficiency. Its all about fuel efficiency vs time. If you care about fuel efficiency and nothing else, drive 30mph. If you are in a hurry, drive fast. If you want to balance your time spent in your car with getting the best fuel efficiency, go with the point where you maximize the area under the curve.

If someone were paying us by the hour to drive our cars, then this is where your interpretation of the graph would be valid. A company would want to balance the time we spent in the car on the way to a job (assuming dirt cheap pay rates), with the amount of fuel used. Cost vs time.

30mph = 80mpg, at a rate of .375 gallons per hour
60mph = 50mpg, at a rate of 1.2 gallons per hour

Lets drive 120 miles.

At 30 mph, it will take 4 hours, but will only take 2 hours at 60 mph.

4 * .375 = 1.5 gallons used in 120 miles, 120 miles divided by 1.5 gallons is 80 mpg.
2 * 1.2 = 2.4 gallons used in 120 miles, 120 miles divided by 2.4 gallons is 50 mpg

What I would be very interested to know is around town what is the best speed to go.

I frequently find myself driving 5 mph under just because I think it might save a bit more gas.

I allways have problems between 30-40mph. It's that spot where, if the road is flat I want 5th gear, but if its at all uphill I want fourth. If I drop down to the 20's and the road goes uphill I sometimes stay in fourth instead of shifting down to third.

I would be very interested in a graph that shows what speed around town gets the best gas mileage and in what gear. If the study concludes that driving at 40mph in 5th (which is fast enough to overcome the uphills) is better then say 30mph in 4th I would much rather go 5 mph over the 35mph speed limit (of most streets).

Right now I drive like a grandma and try and stay away from 35mph roads. So far I find myself at half a tank of gas and have gone 225+ miles (90% city). So something is working.

geometro had a post http://www.teamswift.net/viewtopic.php?t=22137 showing the differences at 40mph between all gears, but it wouldn't really tell you if crusing at 30 in 4th is better than 40 in 5th. I try to stay in 5th as long as I can, usually switching to 4th makes the car more touchy when being really light on the pedal (wants to decel/cut fuel).

One interesting thing about the link above is that geometro only got 55.9 mpg at 40mph, whereas in this test got 72.. I didn't notice this before. Any ideas?

Crap.

I replied with a good post, but I lost it.

Anyway. I think you're right. Efficiency in this graph is related to time.

I was going to post more about the metering of the those figures...but i'm out of time now. I do question the figures and metering technique. That line is too linear (straight) for me. We all know that engines have peaks for power and efficiency. That graph shows almost none. I wonder how the meter works. What does it use to calculate the figures? Does it actually monitor gas flow rate? Probably not. It's probably a calculation of engine speed, gear ratios and estimated MPG....making it linear.

Tell us more about that meter!

Gotta run. I've been here way too long.

Now you're asking the right questions

I always figured the scangauge looks at injector pulse width and duty cycle multiplied by a constant (injector lbs/hr and assumed fuel pressure) to determine how much fuel is being used. Punch in your speed and you have your mpg figure. If this is the case, then any change in fuel pressure would throw off your results. I'm pretty sure this is how all of the factory systems that come with a fuel computer have worked in the past. Maybe it uses another method..

As far as the chart being linear, I expected it to be slightly more curved, especially toward the higher speeds, considering the drag is really starting to become an issue. Maybe geometro's wheel skirts and grille covering are making a difference at those speeds. I still plan on fabbing up some belly pans sometime.

nice discussion... i will stay in background

http://scangauge.com/faqs.htm

QUESTION: How can the ScanGauge do all of these things with only a single connection to the vehicle?
ANSWER: Since 1996, all cars and light trucks sold in the US have been required by law to have an On-Board-Diagnostic version 2 (OBD2 or OBD II) connector inside the passenger compartment. It is required to provide diagnostic information and allow resetting of the CHECK ENGINE light. It also provides a lot of other operating information. The ScanGauge performs the diagnostics functions like a conventional scan tool. It also goes beyond this and uses the other data to add many more useful functions.

That doesn't say much. Here's more.

QUESTION: The MPG gauge reading changes very quickly with slight changes in throttle or load. Can I smooth this out to better determine the affect of speed on fuel economy?
ANSWER: Yes, use the TRIP MPG function in the CURRENT mode. After reaching the desired speed, reset the TRIP. The average MPG since it was reset will be reported.

QUESTION: Can the ScanGauge show if there is a difference in MPG between using my truck with the tailgate up or down?
ANSWER: Yes. See [url]Tailgate Up/Down and Gas Mileage[/url]. http://scangauge.com/tailgate.htm

$124.95 (Includes shipping)

I'm going to take this in a slightly different direction. I've been thinking of this for a while.

Most you guys already took out your Air Conditioner for performance. So...what if you added an electric motor in it's place that you could turn on whenever you hit the AC button? Awesome right! I thought of that myself. (I think I mentioned it here a while back) Well there's a company out there that already has a similar design but they replace the alternator instead.....

http://www.sigmaautomotive.com/electroc ... harger.php

having read the scangauge site, you now know as much as i do about how it calculates fuel consumption.

it also takes into consideration:

- open/closed loop status
- engine displacement (this is a constant the user enters into the unit)

i can vouch for its accuracy: i've been using it since last fall, and it's typically within 1 or 2 percent of fuel used at the end of the tank (usually slightly optimistic).

the unit is also adjustable - you can correct for distance errors and fuel consumption errors by entering a correction factor. (i haven't tried to make it more accurate yet.)