Aerocivic - how to drop your Cd from 0.31 to 0.17

[serialk11r]

Originally Posted by ECONORAM

@serialk11r, take a look at the wheel wells of a RAM pickup. The entire wheel well is radiused. But it could probably use a little refinement wrt to the ecomodder realm...

Had to look kind of hard to find. An 07 like yours: http://static.cargurus.com/images/si...pic-11265.jpeg

But the new ones don't, they have the goofy bulged lip fenders like my MR2.

Makes me wonder, maybe there's an easy, discrete way to extend the fender into the wheel well to get the radius effect. A bodykit can easily be modified to have radiused edges but I don't like bodykits.

[3-Wheeler]

Originally Posted by johnlvs2run

.....2) Your comment about keeping rpm close to 3000 rpm is interesting, but seems counterintuitive due to more stress on the engine, a longer time going up the hill and seems it would put more stress on the cooling. Would going a lower gear at higher rpm actually help the cooling?....

Ah,

Talking about counter-intuitive!!

Kinetic Energy = WV^2/2g

This is one form on an equation for moving a mass up a hill. Work out some numbers and one quickly sees that going up a hill faster simply takes more energy.

Since we are trying to save fuel, it makes sense that going up the hill slower takes less energy (think force times distance divided by time or F * D / T). However, taken to an extreme, going up a hill in first gear may use more fuel than going up in third for example.

I always watch the FCD in the Insight when going up hills to get a feel for what works best.

In the case of the hills by LaCross, going up in third was way better than a higher gear, and keeping the speed to around 30 mph.

Regarding engine cooling.... About 1/3 of the HP generated by an engine goes into the radiator as heat. If we go up the hill slower, use less energy, then it goes that there should be less heat as well, and less cooling requirements from the radiator. However, again taken to an extreme, going to slow lowers the air velocity through the radiator, and thus at some point would heat it up higher because of the slow speed.

In my case, the lower engine temperatures I saw told me that the speed, engine rpm, and gear worked, because engine temperature was lower than going up in forth, with more engine load.

Jim.

[aerohead]

Originally Posted by 3-Wheeler

Ah,

Talking about counter-intuitive!!

Kinetic Energy = WV^2/2g

This is one form on an equation for moving a mass up a hill. Work out some numbers and one quickly sees that going up a hill faster simply takes more energy.

Since we are trying to save fuel, it makes sense that going up the hill slower takes less energy (think force times distance divided by time or F * D / T). However, taken to an extreme, going up a hill in first gear may use more fuel than going up in third for example.

I always watch the FCD in the Insight when going up hills to get a feel for what works best.

In the case of the hills by LaCross, going up in third was way better than a higher gear, and keeping the speed to around 30 mph.

Regarding engine cooling.... About 1/3 of the HP generated by an engine goes into the radiator as heat. If we go up the hill slower, use less energy, then it goes that there should be less heat as well, and less cooling requirements from the radiator. However, again taken to an extreme, going to slow lowers the air velocity through the radiator, and thus at some point would heat it up higher because of the slow speed.

In my case, the lower engine temperatures I saw told me that the speed, engine rpm, and gear worked, because engine temperature was lower than going up in forth, with more engine load.

Jim.

In an article about the old Mobil Economy Run,some Chrysler guys said that they pre-tested their car for every road grade that would be encountered on the run.
An optimum velocity was recorded for each grade,and a ball bearing inside a constant-radius ashtray bottom served as an 'inclinometer' for the team.Some other competitors used a stopwatch hanging from the rear-view mirror to gauge the road grades.
If you construct a graph of the speed/grade/velocity you find a relationship to a constant 'climb rate' of vertical feet per unit of time across the carpet graph that they want to maintain to keep the engine in a BSFC 'sweet-spot.'

[j12piprius]

Originally Posted by 3-Wheeler

Since we are trying to save fuel, it makes sense that going up the hill slower takes less energy (think force times distance divided by time or F * D / T). However, taken to an extreme, going up a hill in first gear may use more fuel than going up in third for example.

I always watch the FCD

If we go up the hill slower, use less energy, then it goes that there should be less heat as well, and less cooling requirements from the radiator.

What is FCD?

The contradictory thing is that instant mpg is lower going up in 5th than in 4th, unless the speed is significantly less, giving the appearance of less energy used (less fuel) and less heat generated in 5th gear. On the other hand, I could always spin up a hill faster in a moderately low gear on a bicycle than a higher one, the sweet spot being 96 to 102 rpm. However I didn't equate that to energy use, figuring I was using more energy but the leverage was more optimal. Also, using a too high of gear on a bicycle changes the dynamic to strength. Maybe there's not a relationship to a car, except to see that higher rpms up to a certain point can be good, but maybe it's the same in a car, as the higher rpms provide better leverage, and thereby, (assumption) less heat.

I do think the higher rpms would reduce mpg, though that's a secondary consideration to keeping cooling in range.

[3-Wheeler]

Originally Posted by aerohead

....If you construct a graph of the speed/grade/velocity you find a relationship to a constant 'climb rate' of vertical feet per unit of time across the carpet graph that they want to maintain to keep the engine in a BSFC 'sweet-spot.'

Hi Phil,

I have been noticing that same effect this year when going up hills. My fuel consumption this year is higher than last year when driving over the same hills to/from work.

I started paying more attention to speed, gearing, rpm's, engine load, and so on over these hills. This is the biggest bang-for-the-buck. See link below for details.

http://ecomodder.com/forum/showthrea...omy-29047.html

The Insight has lean burn, and keeping the car in this run mode over hills can sometimes be quite challenging.

Like you mentioned above about BSFC, I have been tackling hills, sometimes in a lower gear/more rpm, and the results seem to favor this over lugging the engine in a higher gear.

There does seem to be an "art" to driving efficiently. I've had the car now some five years, and still learning a bunch.

Jim.

[3-Wheeler]

Originally Posted by johnlvs2run

What is FCD?

Fuel Consumption Display. The Honda Insight has an instant MPG display that really helps while driving. It's a bar graph that runs across the bottom (left-right) of the dash display.

Originally Posted by johnlvs2run

I do think the higher rpms would reduce mpg, though that's a secondary consideration to keeping cooling in range.

Agreed. Phil touched on BSFC in his comments above.

I am finding that I can get better MPG even on a 1 degree grade hill, by running in forth at a slightly slower speed, than fifth at a slightly higher speed. Sometimes I'll try each just to see for sure.

Jim.

[j12piprius]

Originally Posted by 3-Wheeler

I can get better MPG even on a 1 degree grade hill, by running in forth at a slightly slower speed, than fifth at a slightly higher speed.

If I understand correctly, this means going up the high at a much lower speed in 4th gear, but the rpms can be higher than they were in 5th. For example if I'm going up at 45 mph in 5th, then I'd need to go up at an equivalent instant mpg, thus 36 or so mph, for the overall mileage to not decrease. As the rpms can be higher in 4th, then perhaps the speed would be higher than 36 mph.

[aerohead]

Originally Posted by 3-Wheeler

Hi Phil,

I have been noticing that same effect this year when going up hills. My fuel consumption this year is higher than last year when driving over the same hills to/from work.

I started paying more attention to speed, gearing, rpm's, engine load, and so on over these hills. This is the biggest bang-for-the-buck. See link below for details.

http://ecomodder.com/forum/showthrea...omy-29047.html

The Insight has lean burn, and keeping the car in this run mode over hills can sometimes be quite challenging.

Like you mentioned above about BSFC, I have been tackling hills, sometimes in a lower gear/more rpm, and the results seem to favor this over lugging the engine in a higher gear.

There does seem to be an "art" to driving efficiently. I've had the car now some five years, and still learning a bunch.

Jim.

The beauty of your on-board electronics is that you could take a day and just drive around with different scenarios,documenting as you go,then at your leisure,sit down and 'take it all in',constructing a map for different driving conditions.So sweet!
With my tank-mileage limitations it's hard to infer what the ramifications of a certain leg of a trip might have been.

[j12piprius]

Originally Posted by diesel_john

http://ecomodder.com/forum/showthread.php/aerocivic-how-drop-your-cd-0-31-0-a-290-3.html#post6607

That's an amazing bumper plus wrap around skirts. Can Diesel_John or someone else provide some details of this car, and results of the mods? Specifically, do the advantages of the aero wheel skirts outweigh the disadvantage of higher drag.

[freebeard]

Yes, and why did they park like that?