Why mpg testing is difficult and variable...
There are many variations on the approaches to engine and fuel management design by engineers from many different cultures...the only common ground in the US being the fuel used and the EPA emissions regs.
Also each vehicle might have a different total mileage and state of tune....and possibly other modifications from stock. So a modification that might increase mpg on one vehicle...won't necessarily have the same effect on another. So this might be why using an A-B-A testing method with statistical analysis might be a kind of overkill. Though with a good mpg readout method and a good test route...that might not be so relative to one particular car. Main point is: even if you do careful testing of a mod on one car and find it doesn't increase mpg...that doesn't mean this mod might not work on another car. 1) you might not have set it up right...the devil is in the details? 2) this kind of mod just might not work on this particular car? So...to try and extrapolate from testing an mpg mod on one car to all cars...is NOT statistically acceptable? |
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Fuel is wasted in several different areas: Load at highway speed: 1) In heating up the air through turbulence (high CdA) 2) In heating up the tyres and the road (high Crr tyres) Engine/transmission efficiency: 3) In an engine that is in too high an rpm range for the load 4) In an engine that is too large for the load. 5) In too many, inefficient parasitic loads on the engine (alternator, pumps, etc) In braking: 6) Through an overly heavy car 7) Because we heat up brake pads/discs/drums instead of returning kinetic energy to a battery. 2, 6 and 7 mainly apply in city driving. The rest apply to highway driving. FE in a car can be visualized as being constrained by three bottlenecks. Attack one bottleneck, and eventually you approach diminishing returns. For example, start off with a car built like a brick and geared for city driving. Do some aero mods, and the highway performance will improve. Do more mods and it may not improve the FE much, because the gearing will be much too high for the steady state load. Note that in each of those different areas, it is possible to measure the variables and so compute a function that will give a good approximation as to expected FE. However, it's more complex than saying "Do this and get X increase". Now, since most driving is done in the city, it makes sense for car companies to attack the braking issue, and the only way to do that is with electric technology - you can't turn kinetic energy back into gasoline again. Hence the hybrid car - one with both a gas and electric motor. However, if you can solve the other problems (i.e. decreasing the load on the engine), you can do away with the gasoline engine entirely and go solely to electrical, as range is a major factor in EVs not catching on. I would say that as gs.org gets more of an understanding, people will learn how to measure and understand the effect of the different variables in their car, in the same way as people currently understand the interplay between different variables in producing a fast quarter mile time etc. |
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But all results need to be repeatable and that's where A-B-A testing comes in. To even say a device works on one specific vehicle needs to be able to be proven over and over - at any time on any day in any season. With something as highly variable as FE I don't find statistical analysis to be overkill at all. It gives you the ability to make educated guesstimates much closer to the truth than evidence with unestablished baselines will. Since FE is already variable and testing adds more variables you have to have accurate data to build on to ascertain baselines, margins of error, and to be able to separate real results from flukes and assumptions. |
Nice, 95Metro.
If you don't do proper testing, then you open yourself to trusting all sorts of things from snakeoil to duct tape. |
I'm with you 100%, 95Metro - defender of A-B-A and otherwise controlled-testing!
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MetroMPG - The Great Testing Guru! You've proven over and over again just how important proper testing is. :D
Between your site (which you need to update! :p ) and Tony's fuelsaving site I've come to understand how important it is. At least I won't be performing anymore acetone "tests" (see links) like I originally did when I was new to the world of FE...:D :o https://www3.telus.net/metro/log/nov0305.htm https://www3.telus.net/metro/log/nov1805.htm |
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Seriously though, an extra stop in the city could cause you your new MPG record. When on the freeway/interstate you can easily use the same route, same lane, etc. The variables you'll have (temperature, weather, etc.) can be quantified and can be taken out of the equation. |
20/20 last night they interviewed the Turbonator inventor - apparently it does NOT work but they have sold 150,000 units and say that it does. Also intervieved a platium gas additive that works in MOST cars to improve mileage again another failure when tested by EPA however they rely on car vibration / motion to add the chemical and EPA runs on a dyno.
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Here is a chart showing the results of tank to tank testing.
Notice the mpg difference between the dark blue line (2000) and the light orange line...same period in 2006...showing mpg gains. Avg on this line in 2001 is about 21 mpg...in 2006 it's about 26.5 mpg...around a 26% gain. Notice the green arrow showing where I started testing acetone and an FA2000 in 2004. The poor results in early 2004 were due partially to a failing AC control which ran the AC too much. The FA2000 didn't contribute much due to my thinking it was open too far, while the real problem was a lack of a shraeder valve to keep the raw gas from overloading the O2. So actually it was shut off most of the time. Easy to see the time of the year (ambient temps) vs mpg. There are gaps where the car wasn't driven. No records for 2001 thru 2003. |
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Real testing is a PITA...takes some time & resolve to be impartial and see it thru. |
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And its true that highway is more fun because the numbers are higher. |
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You should be able to isolate the Cr in much the same way, with a coast down test at low speed. Again, with the appropriate electonic apparatus, it should be well possible to measure the efficiency of the engine at different rpm and throttle points, and an intelligent decision can be made on how to gear it. All this requires knowing exactly how your intented modification will improve fuel economy, and directly measuring it, because it IS possible. Which is why I'm inherently skeptical of the various engine additives. If it was cost effective, oil companies would have already done it by now. But the reason those things sell is because they are cheap to produce and the profit margins on those things are high. Americans in general want a "quick fix". And that's why you will never see a map of engine efficiency vs rpm and throttle position included with any of the fuel economy nostrums marketed to the gullible - they can't produce one. And so they are careful to make their claims ambiguous enough and offer a guarantee if it doesn't work, so that they can't be sued for false advertising. Quote:
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The EPA is controlled by the White House and the Legislature. Both mostly represent big oil, car makers, and other business interests. People get elected by using $$ from these interests. So the refiners still refine poorer quality fuels...automakers are not made to improve mileage...the whole corn into ethanol thing is a subsidy for the farmers and Cargill? Also...think about the taxes gasoline/diesel bring in. If they seriously do something like passing stricter CARB standards...there goes the tax base? They wanted to pass a tax on hybrids cause they wouldn't be paying their fair share for road repairs....seeing the light? |
Originally Posted by Mighty Mira
If it was cost effective, oil companies would have already done it by now. Quote:
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Hmmm.
Engine additives have to have a physical mechanism for improving fuel economy. Somehow, they have to enable more power per stroke. i.e. they have to: a) produce more gas (expansion) than gasoline already does b) reduce knock (premature detonation) so that compression can be ratcheted up, and hence efficiency (like a diesel). c) somehow increase completeness of combustion. There has to be a mechanism by which a substance does this. Tetraethyl lead performed b) for years, very effectively. Only because it was poisonous was it stopped. And then there is MBTE, toluene, benzene. They are added in various countries. If you wanted to increase fuel economy regardless of emissions, you could find a way to get these chemicals and put them in the tank, provided you had a way of increasing your compression to benefit from their use. If you were willing to go that far, direct injection also works wonders. Suffice to say, it is an advantage for individual oil companies to provide gasoline that will be more efficient. It is neither in their interest nor the car companies for you to use something else entirely. |
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One guy has found an additive that is supposed to give around a 50% mpg gain on the highway...when combined with advanced ignition. He uses something that increases the octane. Acetone...xylene...GP7 (PIB).....mothballs all increase octane. Though I typically use advanced ignition....I've yet to have the sense to adjust the advance to the additives used. Guess the idea is to start the burn early...and let it play out longer....result being a more complete burn? As far as the refiners....I think the EPA prevents them from producing designer fuels...there is something on the web about one gas company that tested a new fuel around the world as a stunt. The EPA focuses on pollution levels...forcing the automakers to manage good pollution levels using poor fuels? The sane way would be to make the refiners produce high mpg fuels and the automakers to reach for much higher mpg levels. But there goes the tax base...and the excuse for oil wars. It's all about $$? |
OBD II reader for mileage?
Hi folks,
I am new to this web site, but not entirely new to improving efficiency. I have a rediculous amature interest in aerodynamics, particularly as it pertains to racing, but more recently I have directed this towards fuel savings as well. I am very interested in accurately measuring gas mileage. So far, I have been using the miles driven / gallons to fill tank method. I'd like to find something more accurate, and I know that a number of new cars have instantaneous and trip mileage functions (as quoted in Car and Driver). What sort of devices do you folks use? Is there a good OBD II plug-in that determines fuel consumption from pressure / injector pulse width or similar? I suspect that this has been covered in detail before, and if someone would be kind enough to offer a link to the thread or threads, I'd be most appreciative. Thanks much, and I hope that over time I will be able to add to the knowledge base on this site. Bman '98 Saturn SL2 & '06 PT Cruiser commuters, '83 GL Mustang race car |
I just read some posts about the SuperMID. I should specify that both of my applications (Saturn and PT) are OBD II capable. Are there more offerings for OBD II cars?
Thanks! Bman |
Scangauge is the simplest solution for OBD2 vehicles. scangauge.com
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I'll investigate.
Thanks, MetroMPG. Bman |
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