Why mpg testing is difficult and variable...

[ZugyNA]

Originally Posted by MetroMPG

I'm with you 100%, 95Metro - defender of A-B-A and otherwise controlled-testing!

I'm waiting to see more of that really fine testing show up on your website!

[ZugyNA]

Originally Posted by 95metro

MetroMPG - The Great Testing Guru! You've proven over and over again just how important proper testing is.

Between your site (which you need to update! ) 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...

Gee. Maybe you didn't account for falling ambient temps? Sometimes it takes several tanks to see results with acetone.

Real testing is a PITA...takes some time & resolve to be impartial and see it thru.

[cheapybob]

Originally Posted by Matt Timion

Agreed... besides, when you only test highway you get better bragging rights :P

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.

If you really were willing to put in the effort, you could come up with a test route to run in an empty parking lot with timed idling stops and consistent throttle amount and shift/braking points. You'd also need an accurate scangage or equiv for this to work.

And its true that highway is more fun because the numbers are higher.

[krousdb]

Originally Posted by cheapybob

And its true that highway is more fun because the numbers are higher.

City numbers are better for me....

[Mighty Mira]

Originally Posted by cheapybob

All those things are variables, and the more variables you have the less likely that consistant results will result.

While that is true, it is possible to isolate those variables. If you know the Cr of the tyres, it is possible on a calm day to do a high speed coast down test and accurately assess the change in Cd. This will be very accurate if you have an electronic device to assist your testing.

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.

Originally Posted by cheapybob

Skip the attempt at "city" testing, IMO. Its hopeless to get non-variable conditions. Even on a highway test its difficult.

Agreed.

[ZugyNA]

Originally Posted by Mighty Mira

If it was cost effective, oil companies would have already done it by now.

What you need to know?

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?

[diamondlarry]

Originally Posted by Mighty Mira
If it was cost effective, oil companies would have already done it by now.

Originally Posted by ZugyNA

What you need to know?

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?

It isn't cost effective for them to do it. They will never do those things because it would benfit/be cost effective for us not them.

[Mighty Mira]

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.

[ZugyNA]

Originally Posted by Mighty Mira

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.

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 $$?

[Bman83GL]

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