2006 in review: mods vs. technique. And the winner is...
 

Driving technique won over mods by a pretty wide margin: 37.5% vs. 28.0%. Though you'll have to buy into my "comparison" method to believe it. It's pretty inexact (to say the least...)

Tallying just the mods ...

5.2% tranny swap
http://www.metrompg.com/posts/tranny-swap.htm

10.3% alternator optional
http://www.metrompg.com/posts/alternator-optional.htm

2.3% kardboard kammback
http://www.metrompg.com/posts/boat-tail-prototype.htm

2.3% mirrors
http://www.metrompg.com/posts/mirrors.htm

5.7% grille block & rear wheel skirts
http://www.metrompg.com/posts/grille...ing-part-2.htm

2.2% undertray

= 28% total theoretical improvement over base from measured mechanical/aero mods

I'll be the first to admit this tally is flawed on several levels: 1) the weather conditions weren't the same for all tests; 2) the speed wasn't exactly the same for all tests (but close to 55 mph); 3) the effects of individually tested aero mods can't simply be summed because their effects interact with one another ... the car is probably more or less than 28% better with all the mods in place. But the car was never driven with all of them in place at one time and then without.

Driving technique ...

To do this comparison, I looked at 3 tanks in Firefly #1 which were predominantly city driving. When I was using that car, I wasn't employing coasting of any form, or P&G/codfishing, and there were none of the mods listed above.

Firefly #1, 3-tank tally: 1474 km, 83% city driving ... 5.2 L/100 km / 54.0 mpg (Imp) / 45.0 mpg (US)

Blackfly, 3-tank tally: 1724 km, 83% city driving ... 3.3L/100 km / 86.5 mpg (Imp) / 72.0 mpg (US)

If you do the math, that actually works out to a 60.2% improvement for the Blackfly.

The biggest flaws in this comparison are: 1) it assumes the "base" cars are identical (which they were on paper, but probably weren't in reality) ; 2) the Blackfly has some mechanical & aero mods on it that the other car
didn't have. Based on the values in the mods list though, we can correct for these mods:

- 5.2% transmission advantage
- 10.3% alternator advantage
- 1.2% aeromods advantage (calculated based on avg. city speed of 25 mph vs 55 mph for the tests)
- 6.0% rolling resistance (this is a WAG - the Blackfly has LRR tires and higher pressures than the first Firefly had)

------
-22.7% total deductions (this is actually a liberal estimate, because the Blackfly was not running alternator-less, nor with all aero mods, and the taller tranny was only in place for 2 of the 3 tanks)

= 37.5% estimated difference due to driving technique

Only a piece of the puzzle
 

Technique is great, but what if you want to just hop in the vehicle and drive reasonably?

I prefer to rely on mods more. Besides, if someone else drives the car, those fuel saving devices are in place.

Best of all, I suppose, is to start with a great platform.

I'll admit, I had the biggest jump with extreme technique, but it wears on more than just the longevity of vehicle components. I'll still engine-off coast now and then -- but not as often, for example :o

RH77

Ahhh, but the cost to change techniques is priceless.:p. You don't have to be completely radical to show a huge increase if FE with techniques alone.

People will have different approaches to saving gas, and that's to be expected.

But there's no question that adjusting the nut behind the wheel is the easiest & cheapest approach. It also has the benefit of being portable - you can take it to every vehicle you drive. Can't do that with mods.

True
 

True, very true. Let me play the Devil's Advocate here. But how then to promote the site? Mods imply wrenching (espcially with the logo). Perhaps both points-of-view could be represented and let the user decide? Same for extreme technique vs. emissions, etc...

But yep, Z has the point of them being Absolutely Free!!!

-R

You can mod your car and/or your driving.

Both approaches will be embraced - it's all good here.

That's what I was envisioning -- good stuff.

-R

Both are useful. I'm just fixated on the idea that the power actually required to move a person and groceries, rain or shine, at highway speeds (ar or near) is at least an order of magnitude less than the current average mode of transport.

I'm also frustrated at the limits of my car and don't like the constraints imposed by the automotive industry. I know that what I'd like (and what the world needs) can be designed and only has to be designed once, then mass produced. It might also be possible that retrofitting is an option - the only problem is that the cars out there are all different, so there is no one size fits all solution - you can only target low hanging fruit, where the modifications are easy and significant.

Modifying the car serves several purposes:
1. Further improvements to FE after adjusting the nut behind the wheel has approached diminishing returns.
2. Proof of concept that load on engine can be further reduced at highway speeds (aero).
3. A starting point for reducing fuel consumption given that smaller load, or switching powerplants.

A logical endpoint is the VW 1 litre car, or something like a heavily faired Honda Cub.

Modifying the driver is always going to have a great return - barring some sort of miraculous battery technology that is near 100% efficient to charge and discharge, of appropriate weight, etc.

Unfortunately, carmakers are in the "transportainment" industry, not the transportation industry.

As long as vehicles are marketed and purchased as fashion statements, we're going to get foolish un-aerodynamic designs like the Volt for a vehicle that's (going to be) laughably held up as an icon of efficiency in North American transportation options.

And you're also right - even if it triples the average fuel economy of the US fleet, the volt is 10x more vehicle than we need.

This guy is moving in the right direction with the BugE.

I say mods support and assist better technique.
The two work together for a synergistic effect.

Many of my mods decrease rolling resistance or air drag; some reduce engine load (e-fan). Without reducing rr and drag, P&G was nearly worthless. It wouldn't coast. Now with hard tires and some aero mods it will coast nearly anywhere, though still loses some speed of course.

Also if you consider adding SG or SuperMid to be a mod, then that also supports improved technique.

Thanks for bringing this back on track. That's a key point.

Absolutely.

Ultimately, what we are attempting to do is minimize Delta E/ Delta s, or the net loss of energy over distance traveled. Since Delta E is the same as work, or Force * Delta s (force through distance), the Delta s' cancel and we are left with Force. Assuming an engine of constant efficiency, if we minimize force (drag + rolling resistance) we are maximizing fuel economy.

Pulse and glide is a method of driving in which the assumption of constant efficiency is a better one, since the engine is operating near its peak efficiency or is consuming negligible amounts of fuel otherwise. What will throw this out:
-engine is large and the car forced to idle (in the glide section)
-gearing such that the rpm are far above 2300, e.g. in my car, I'm using up to 17% more fuel than my engine needs to in order to produce a given power at 100kph.

Air resistance force increases as the square of speed. This means that if we can halve* the CdA, it's the same in terms of load as if we were driving at 1/(2^.5) or 71% of the current speed in the unmodified car. e.g. Driving at 100kph becomes like driving at 70kph the way you used to, or if you are driving at 80kph, it's like you were driving at 57kph in your old car.

So yeah, the long and the short of it is that there is a synergistic effect going on, pulse and glide works best with a low CdA. Pulse and glide with a high CdA car is a lot of effort for little gain and wear and tear on the clutch. Aero mods alone don't do much when the engine is expending lots of fuel to turn itself at high rpm.

*Halving the drag coefficient is a big ask. I'll suspect that I'll get close (est. 0.20) with the front skirts, but the only way I'm going to get better than that is to go basjoos style and extend the boattail further, or experiment with turbulators and a more extremely angled boattail.

Agreed. It's why the Honda Insight was/is a FE monster in the hands of a determined hypermiler. Light weight + low drag (aero, rolling & mechanical).

Another point I've been thinking about lately is that light weight (lower momentum) tends to reveal the impact of poor aerodynamics much more dramatically in a P&G scenario than a heavier vehicle with similar CdA.

I read an account of the Daimler smart car recently where the driver was somewhat surprised/perplexed by its poor coasting ability. At ~1600 lbs (-ish), with that shape, I wasn't surprised at all.

Exactly. It's very similar to terminal velocity down a particular gradient. I'd forgotten that until creating my P&G calculator forced me go through the calculations. Ignoring driver and other weight will also throw out your drag coefficient calculations from coast down time.

I have to confess I didn't get to the GS thread about the P&G calculator.

I'm amending it for 4 valve per cylinder engines (such as mine), and improving it so that it's easier and less intimidating to use (i.e. automating engine map lookup). Will post here after it's finished.

I've put a new version on ecomodder. Now you have no excuse not to try it out, and it even looks up an approximate BSFC number for you and everything.

Being able to flick back and forth different speeds without checking up on a map really rams home both the difference going slower makes, and also the differences aero mods can make.

e.g. On my car (everything is P&G):
100kph, initial drag: 3.97l/100km
80kph, initial drag: 2.6337l/100km
100kph, modded to current state: 3.03l/100km
80kph, modded to current state: 2.1048 l/100km

That's a good 25% increase.