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Hi folks,

I am the proud owner of #169, got it this weekend and have commuted to work twice in it so far, 45 miles each way. On the trip home today I achieved 76MPH driving 60-65mph. It is just such a privilege to own such a car!

I have been interested in the Insight for sometime now. Last Christmas, I was having a chat with my brother-in-law, a GM at a Honda dealership, and expressed my interest to him. He immediately said “ oh, you don’t want that car, people can’t get rid of them, they are going for $3000 at the auctions”. $3000!?!?: now my interest was really peaked (sp?). I did my research, found a decent one well below market value and the rest is history. And speaking of research, my hats off to the contributors of the forum and site in general. Thank you. These cars are way under-valued, and the only reason I can figure is that ignorance begets fear. This site helped me to move forward confidently.

To add my two cents to the forum, I’ve notice many comments regarding poor fuel economy during the winter and seems that nobody has really hit the nail on the head, or perhaps I missed it. The most significant contributing factor in this case is the increased density of the air. The heavier air is actually more difficult to penetrate. To further expound, aircraft pilots talk about Altitude Density, in which heat, altitude and dew point all play a factor. Simply put, the greater the altitude, the higher the humidity and the hotter the air, the “thinner” the air and the greater the Altitude Density. For airplanes high altitude density is bad, but for the high MPG vehicles such as the Insight, a high altitude density will improve its economy up to the point that the engine can cope with such conditions.

cheers
 

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And welcome to the group. Your post title caught my attention - my X always said I was a little 'dense' :wink: You didn't mention - how many miles does it have and what's the life time MPG :?:
 

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John Miller wrote:

> To add my two cents to the forum, I’ve notice many comments regarding
> poor fuel economy during the winter and seems that nobody has really
> hit the nail on the head,or perhaps I missed it. The most significant
> contributing factor in this case is the increased density of the air.
> The heavier air is actually more difficult to penetrate. To further
> expound, aircraft pilots talk about Altitude Density, in which heat,
> altitude and dew point all play a factor. Simply put, the greater the
> altitude, the higher the humidity and the hotter the air, the
> “thinner” the air and the greater the Altitude Density. For airplanes
> high altitude density is bad, but for the high MPG vehicles such as
> the Insight, a high altitude density will improve its economy up to
> the point that the engine can cope with such conditions.


Interesting concepts.

As a pilot myself can I nit pick a bit, please?

The term is density altitude. Which effects both the engines ability to produce _power_ and the wings ability to produce lift. In small aircraft the effect is great enough that under some conditions takeoff will be impossible. e.g. load, density altitude, and runway length in combination are insufficient. In larger aircraft takeoff procedures must compensate for the altitude effect to maintain margins of safety.
Even military fighter jets must take this into consideration. As I remember there was a fatal crash on takeoff in the late 60's or early 70's that was a result of rapidly changing density altitude conditions which the pilot failed to compensate for.

More On Topic to the Insight:

It is indisputable that to develop more _power_ you need a higher density of intake charge (heavier fuel:air mix) However, for maximum MPG other factors come into play. Specifically the "lean burn" mode that a 5spd (sorry CVT'ers) will enter to achieve the ultimate high MPG values you read about in here.

Ideal conditions for maximum MPG appear to be high humidity with moderate temperatures (upper 70's to low 80's) with intake air temps (IAT sensor readings) in the upper 110's to 120's (using a hot air bypass to the standard intake tube). This by definition ia a relatively high (thinner, less power) density altitude "day" for the engines intake charge. In theory the high IAT improves the fuels ability to atomize. This improves combustion efficiency at the expense of power. And is apparently designed into the Insights fuel management controls. This is counter intuitive to how an internal combustion engine produces efficient power. A natural deduction is that increased power from an engine of the same displacement and aspiration = increased MPG. If you let your Insight teach you, I think you'll find it to be otherwise.

Air density as it related to aerodynamic drag is a factor, and exponentially so at higher speeds. This is why you'll see rapid MPG fall off above 65 MPH for any density altitude (its effect is negligible below 40 MPH). The aero drag density effect is definitely measurable and probably visible on the Insight's MPG indicator if all other factors could be isolated. But I am of the opinion that it is the smallest percentage of MPG loss vs. cold engine inefficiency and fuel atomization. And given its known exponential factor it does not sufficiently explain the winter MPG drop-off for those of us that infrequently venture into the 55+MPH range. <g>

John K. Bullock
aka. Insightful Trekker
 

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Insightful Trekker said:
Air density as it related to aerodynamic drag is a factor, and exponentially so at higher speeds.
Aerodynamic drag is quadratic versus velocity (goes as velocity squared) and linear versus air density. Increased density has as much effect as increased frontal area of the vehicle. If you double the air density, you double the drag on the car.

A temperature change from wicked cold (0 F = -20 C = 255 K) to Death Valley hot (100 F = 40 C = 315 K) is a 20% increase in absolute temperature, with a corresponding 20% decrease in density. So air drag would be reduced by 20% (or increased if you dropped the temperature by that much). There is a bit of rounding off here and there.

Twenty percent increase in drag for the most extreme winter temperature shift you can imagine... but I doubt any of us have seen that much of a temperature shift, and we see much greater MPG losses (I saw 50% or more this past winter).
 

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Insightful Trekker said:
Ideal conditions for maximum MPG appear to be high humidity with moderate temperatures (upper 70's to low 80's) with intake air temps (IAT sensor readings) in the upper 110's to 120's (using a hot air bypass to the standard intake tube <g>

John K. Bullock
aka. Insightful Trekker
So is warm air is better for MPG? I know that cold air is better for HP.

What is this "hot air bypass"? The intake tube is located directly above the intake manifold and has a flexible tube that goes to the resonator located in the front left of the bumper/fender.
 

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Only got mine this spring, but I wonder: could the lower winter mpg be due in part to the extra work done pushing snow & slush out of the way of the tires? Does it happen in the cold, or in the snow?

And as another pilot, may I second Insightful's description of density altitude. Seems like every summer we hear of a pilot or two who flies to Tahoe to Truckee (~6000 ft) from the (sea level) Bay Area, forgets about density altitude, tries to take off on a hot day with a full load of passengers & luggage, and doesn't make it.

That said, in a normally-aspirated prop plane, fuel efficiency does increase the higher you fly.
 

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Discussion Starter #7
Mitch53 said:
And welcome to the group. Your post title caught my attention - my X always said I was a little 'dense' :wink: You didn't mention - how many miles does it have and what's the life time MPG :?:
Thanks :D 31475miles @50 mpg BTW 85.5 mph on the way home from work tonight. drove out the dealer gas this morning an put a fresh tank in. Unbelievable!!!


Tim Maddux said:
with a corresponding 20% decrease in density. So air drag would be reduced by 20%
Your math is off here, as power requirements increase with speed (as you had just quoted as the fourth power) the same can be said of decreased altitude density.

Insightful trekker, also being a pilot, I agree with most of your comments, but as you indicate, the engine efficiency is increased at high altitude density. So if its not the power source, then it must be the increased drag, your comment only supports my position.

You guys are a tough audience, let me further qualify. My aircraft, an air creation trike, will climb about 1000 ft/min on a high altitude density day, but given a nice clear winter day, that performance will increase to over 1500 ft/min, and that is given the same engine rpm implying that the power setting is the same. Thats over 50%!!

I also validated this with one a owner of a pure electric car. he notes a considerable decrease in range on low altitude density days.

I know it unfathomable, we sit down here breathing the stuff and cant tell any difference, but experience has taught me otherwise.

best regards
 

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james said:
That said, in a normally-aspirated prop plane, fuel efficiency does increase the higher you fly.
Again altitude density is increased and there is less drag on the airplane. This is the sole reson why commerical airlines fly so high. too bad we can cruise at 35,000 ft :wink:

cheers
 

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liteflier said:
Your math is off here, as power requirements increase with speed (as you had just quoted as the fourth power) the same can be said of decreased altitude density.
Drag is linearly proportional to density and quadratically proportional to velocity. Quadratic is velocity squared. Your fuel consumption rate must be enough, in a cruise, to overcome drag.

Distance per gallon / energy per gallon is energy expended per unit distance. Energy expended per unit distance is the work done to move the car, divided by the distance the car moves. Which is drag. So, a 20% reduction in drag comes from a 20% decrease in density and that gives a 20% decrease in fuel consumption or a 20% increase in MPG.
 

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Tim Maddux said:
Drag is linearly proportional to density and quadratically proportional to velocity. Quadratic is velocity squared. Your fuel consumption rate must be enough, in a cruise, to overcome drag.
.
oh yeah ... thats what quadratic means, my apologies, i should have read your posting more carefully. I'm also aware that the fuel is different in the winter. but to account for 50% difference in MPG !?!?! your getting <36 MPG during the winter ?! WOW

Reviewing your first post Tim, you referred to temperature ranges, but not altitude density, is this an oversite? Pilots refer to it as the 3 H's, high (altitude), heat and humidity. All three must considered when determing density.
 

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cakley wrote:

<snip>

> So is warm air is better for MPG? I know that cold air is better for HP.

For the Insight, and up to a limit, it appears so. As I outlined above in this thread. And _only_ if you drive in the maximum MPG style to take advantage of it.

> What is this "hot air bypass"? The intake tube is located directly
> above the intake manifold and has a flexible tube that goes to the
> resonator located in the front left of the bumper/fender.

As I remember _someone_ in one of the Yahoo groups started playing around with the idea of an additional tube that routes intake air from the vicinity of the CAT to the engine's intake tube. Remove the last joint of the intake pipe (it unbolts and slips apart without damage). Then add a flexible hot air hose. Accordion aluminum, widely available at discount auto stores for under $10, 1-x/x" ID, I don't remember. Fit it OD to the "stump" you just made. Then route this hose back under the engine "beauty" cover (also requires removal and reinstallation - simple) and position this end in the immediate area above the CAT. The hose must be *carefully* stretched and curved else it will seperate/tear, and will require a bit of crushing/forming to clear some tight spot(s).

This new tube ends up being reasonably close to the length of the removed section of intake pipe so the "tuning" of the intake system is relatively undisturbed.

You've now got a "Hot" intake air "system." Cheap, relatively easy to undo, with no fathomable warranty or durability impact. I installed mine with some skepticism. But with monitoring I do see a "widening" of the "lean burn" window (sorry CVT'ers) that allows higher MPG to be achieved if you'll take advantage of it. If your driving style isn't for maximum MPG then you'll never see the difference.

03 5spd Insight
15k+ miles
LMPG 69.1 and rising
best round trip daily commute MPG 87.4 +- 50 miles
best one way daily commute 91.1 +- 25 miles
commute speed average 50mph max. 55 mph
best tank average 78.8 MPG
 

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Tim Maddux wrote:

<snip>

> Which is drag. So, a 20% reduction in drag comes from a 20%
> decrease in density and that gives a 20% decrease in fuel
> consumption or a 20% increase in MPG.

Thanks for the "math" lesson in regard to my incorrectly defining aerodynamic drag <g>.


However, your math above needs a little tweak. :)

Since aero drag is not the only or biggest (depending on speed) factor in attainable MPG, and since aero drag is not a significant factor below 40 mph a 20% +- change in aero drag for any reason will not directly translate to a 20% change in MPG. Its usually much less. If you want to run your Insight down the road at 100 mph then a 20% reduction in aero drag will closely correspond to a 20% increase in MPG. I'd say you could count on an increase from 25 to a whoppin 30 MPG, until the IMA depleted and you go into a forced charge. <g>
 

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liteflier wrote:

> You guys are a tough audience,...

And you've been a good sport. Thanks :)

However, please re-read my post in regard to density altitude. And study this topic further if needed. Or at least stay close to sea level in your piloting. Except for this being a serious safety issue for pilots (you) I would not expound here further simply as an Insight issue.

Density altitude (as I remember the calculation on a slide rule type pilot aid) is defined in feet above sea level. The "higher" the term (hotter, more humid) the higher the equivalent altitude. Hence, the term density altitude is used to key into the commonly understood loss of performance with increased (higher) altitude that all aircraft exhibit.

The term is _NOT_ used in the physics sense of higher density = more dense = better aircraft performance.

We are probably simply tripping over each other via the written word.

The discussion of turbo-jet engines and altitude efficiencies is farther OT than I care to venture. :)

End of topic for me :))

John K. Bullock
aka. Insightful Trekker
 

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Discussion Starter #14
Insightful Trekker said:
And you've been a good sport. Thanks
Speaking as a good sport, I was wrong to state that whole lean burn thing supported my point. But you must admit that it's not reasonable to think that variations in Altiutde density at sea level whould have such adverse effect on such a finely designed engine. Agreed?

Let me first give my defintion in laymens terms,best I can, of altitude density, which problaby should have preceeded this whole thread. Heat thins air => less dense. and as we know, the higher we are, the less dense the air. So on a hot hot day, it feels like I'm at xxx altitude on a normal day. for example, at 90F near sea level, the air has the same density as it would have at 6000ft on a normal day (59F), so pilots would say "altitude density has increased 6000ft" for this example. To add to this effect, humidy also thins air. So the effect is compounded. So when I talk about altitude density, I'm really saying that the heat and humidity both effect air density (as does altitude). Some may notice that is is harder to breath on hot humid days.

I will a stab, however breif, at commercial airline practices and why that applies to the insight. For sure, altitude density effects aircraft engines adversely, but as altitude density increases, the positive effects on aerodynamic drag far far outweigh the decrease in engine performance ... upto a point. Again, that why airliners fly more efficiently at altitude. (actually the decresed engine perfromance only further improves their efficency).

so how does this effect all us earth bound Insighter's? Lets use sea level as a reference .... as heat increases, air thins. As humity increase, air thins. AS the air thins, the insight is more easily able to slice through the air. the effect is far greater than you'd expect.
 

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Insightful Trekker said:
a 20% +- change in aero drag for any reason will not directly translate to a 20% change in MPG. Its usually much less
Yes, I agree. I would consider that 20% as a maximum bound on the benefit you could get from density changes due to temperature... the original poster was talking about that as the most significant contributing factor to poor winter mileage, and I was offering analysis to debunk it.

I did see this winter a 50% drop in mileage. Density alone cannot be the most significant contributing factor, since there is 30% left over even with an exaggerated contribution due to density.

In cold temps, the car just doesn't run in lean-burn mode as much. It burns gas trying to keep the engine warm, or keeping me warm.
 

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Discussion Starter #16
run the numbers ...
given Altitude=0, temp=0F, Dewpoint=-5F, Pressure=31Hg
Density Altitude -6545 feet, Relative Density 121%

given altitude=0ft Temp=95F, Dewpoint=92F, Pressure=29Hg
Density Altitude 4009 feet, Relative Density 88%

These are totally reasonable numbers. 33% density change != 50% but is significant.
 

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Undervalued

Congratulations on your purchase! The Insight is a wonderful car! It's unbelievable that it is so undervalued. I always find this interesting...that people perceive some things more valuable than others. Like some people would spend hundreds/thousands on a coat and I would not. The Insight shows me that what is popular isn't necessarily good...and vise versa

Enjoy your Insight!
 

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My first calcs were using the ideal gas law. Here's another set using an online calculator. I only changed temperatures, whereas you changed a few things.

http://wahiduddin.net/calc/calc_da_rh.htm

0 ft, 0 F, 30 inHg, 0% RH gives me relative density 113%
0 ft, 95 F, 30 inHg, 0% RH gives me relative density 94%

(113-94)/94 = 20%

Again, you are overestimating the effect of density on cold weather fuel economy by saying it predominates due to aerodynamic drag, not just for the reasons I list but also for the reasons I and others have mentioned (engine performing differently -- especially when it comes to lean burn at temperatures below freezing, aero drag not being as significant).

Interestingly, the lmpg database on this site reports an overall average of 62.23 lmpg for drivers who report a "significant amount" of winter driving and 61.60 lmpg for drivers who report "little or none."
 

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Tim Maddux said:
0 ft, 0 F, 30 inHg, 0% RH gives me relative density 113%
0 ft, 95 F, 30 inHg, 0% RH gives me relative density 94%

(113-94)/94 = 20%
My math is a little rusty ... should my calc be
( 121-88 )/88 = 37.5% ???
I'll have to look into y'all claims closer, not to mention experience a winter with the insight! Thanks for the feedback.

I found my car on Autotrader.com, but cars.com was also an excellent resource.

BTW, the original owner of my car really decked it out, leather interior, custom stripes, a rear spoiler (yikes) and stick on rain gutters (double yikes). I had the rain gutter removed but the spoiler looks like it was actully tapped through the rear glass. Looks cool but not sure what I'll do with it.

cheers
 
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