Diagram: How to Ecomod Your Car

[Old Tele man]

OFF while accelerating = less HP and less FUEL needed

ON while decelerating = recharge while coasting.

[aerohead]

Originally Posted by ConnClark

So it allows them to downsize an engine more to save fuel. If the technique is added to an existing car it would just be a performance enhancement and not a fuel saver. Correct?

I reckon that since transient loads are the least efficient,and steady-state the most efficient,that Honda was killing both birds.
When under acceleration,they were removing some load during this least efficient operation to get the car up to operating velocity,then making up the difference on the battery when the engine was near peak BSFC and would suffer a smaller mpg hit.
The same could have been done with the AC compressor employing a normally-closed vacuum switch which goes open circuit upon loss of manifold vacuum.AC is a major hit with a 60-bhp engine.

[California98Civic]

Originally Posted by Sven7

True, but I always imagine that in 15 or 20 years the old, inefficient designs will have petered out and we will have pre-aeromodded cars all over. That won't happen if design students don't learn about economy. I'm in my last semester at one of the top two automotive design schools in the country and have not heard more than a passing word about aerodynamics.

There was a student who decided he wanted to put giant wind turbines on the car to charge the battery with wind power while driving on the freeway. I'm not going to name names- he's a good guy- but it just kind of shows the lack of instruction in matters not directly relating to drawing, sculpting and aesthetics. The curriculum is lacking.

I guess what I'm trying to say is I'm very glad you're teaching your students about this and helping to create a grassroots ecomodding aftermarket, but what the world really needs is informed design from the drawing board to the factory.

/rant

Nicely said, but the reform of such curriculum is for others (it's not my field). But what I can tell you is that my January course in the histories and cultures of modding cars yielded plans for a new student club focused on modding and scores of stop-bys at my car. Also, my students handed out dozens of copies of your flier, the flier that started this thread. It was very well received. One person picked it up and obviously impressed said "your students made THIS" (a little incredulous). Hahahaha!! I told her no and that a guy from Detroit on ecomodder.com made it. Thanks again...
james

[ConnClark]

Originally Posted by aerohead

I reckon that since transient loads are the least efficient,and steady-state the most efficient,that Honda was killing both birds.
When under acceleration,they were removing some load during this least efficient operation to get the car up to operating velocity,then making up the difference on the battery when the engine was near peak BSFC and would suffer a smaller mpg hit.
The same could have been done with the AC compressor employing a normally-closed vacuum switch which goes open circuit upon loss of manifold vacuum.AC is a major hit with a 60-bhp engine.

So I guess its only a win to use it when your BSFC drops 15% below your average BSFC.

[ChazInMT]

Originally Posted by Gerrelt

Do you mean this one?:

No, this to me is like showing how the rear window on a Model T might work, almost all modern cars (after 1990) have a radius there at the top of the rear glass, this looks like a study in roof to rear glass with no radius. Could care less about Pinto Aero....

But fer sure thanks a ton for finding this bit here, it just wasn't the thing I remember. The diagram had Radius as the variable, not angle.

[Sven7]

Originally Posted by California98Civic

Nicely said, but the reform of such curriculum is for others (it's not my field). But what I can tell you is that my January course in the histories and cultures of modding cars yielded plans for a new student club focused on modding and scores of stop-bys at my car. Also, my students handed out dozens of copies of your flier, the flier that started this thread. It was very well received. One person picked it up and obviously impressed said "your students made THIS" (a little incredulous). Hahahaha!! I told her no and that a guy from Detroit on ecomodder.com made it. Thanks again...
james

Hehe, cool. I'm glad it's well received outside the "cult"!

[aerohead]

Originally Posted by ConnClark

So I guess its only a win to use it when your BSFC drops 15% below your average BSFC.

We may want to think of it on a case specific basis.Those with instantaneous mpg readout could monitor mpg behavior with and without 'n see if it showed on the radar screen.

[aerohead]

Originally Posted by ChazInMT

No, this to me is like showing how the rear window on a Model T might work, almost all modern cars (after 1990) have a radius there at the top of the rear glass, this looks like a study in roof to rear glass with no radius. Could care less about Pinto Aero....

But fer sure thanks a ton for finding this bit here, it just wasn't the thing I remember. The diagram had Radius as the variable, not angle.

In Hucho's book he has eleven graphics depicting Cd as a function of 'sharp' angle roofs.
The last,Fig.4.59 shows optimum angles as a function of length of rear portion of the car.The table shows five different optimum angles for five different lengths.So if you're unfortunate enough to have a roof like this,then you could construct a curve from this scatterplot,and using your own dimensions,find your best angle.
--------------------------------------------------------------------------
Directly following the sharp-edged roof section is Buchheim et al ' work on rounded rooflines.It is this work from which Hucho selects 23-degrees as the maximum recommended slope angle,as is depicted in Fig.4.60.

[ConnClark]

Originally Posted by aerohead

We may want to think of it on a case specific basis.Those with instantaneous mpg readout could monitor mpg behavior with and without 'n see if it showed on the radar screen.

Yes I agree it would be a case by case basis, however I'm not sure that instantaneous mpg readings are going to tell you when you need to enable it.

Looking at the BSFC chart for my car I can see that enabling the alternator below normal road load (slowing down, braking, going down hill, etc) on the engine would be a loss in efficiency. It has to drop quite a ways to cross the threshold of using 15% more fuel where turning the alternator off would be beneficial. Everywhere else that it is above normal road load has better BSFC or is using less than 15% more fuel.

In my case it would be very difficult to determine where my efficiency dropped below normal enough to justify turning the alternator off would actually help.

[aerohead]

Originally Posted by ConnClark

Yes I agree it would be a case by case basis, however I'm not sure that instantaneous mpg readings are going to tell you when you need to enable it.

Looking at the BSFC chart for my car I can see that enabling the alternator below normal road load (slowing down, braking, going down hill, etc) on the engine would be a loss in efficiency. It has to drop quite a ways to cross the threshold of using 15% more fuel where turning the alternator off would be beneficial. Everywhere else that it is above normal road load has better BSFC or is using less than 15% more fuel.

In my case it would be very difficult to determine where my efficiency dropped below normal enough to justify turning the alternator off would actually help.

Honda's logic was probably to partially deplete the battery on acceleration,then during deceleration,load the field coil and let the alternator do some 'engine-braking',bringing the battery up to full charge,rather than waste all the kinetic energy to hydraulic brake heat.
A thing like this would alter the dyno setting at EPA Mobile Sources certification testing,perhaps giving Honda a tasty MPG number to advertise.