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Discussion Starter · #1 ·
While I was looking into the Xado product I saw that Redline did a idle fuel efficiency test. Basically, you let you car go to empty, add a specific amount of gas, and see how long it idles until it runs dry. Because driving methods affect MPG much more than some small gain in efficiency, this seems like an interesting way to compare the efficiency of our engines.

Possible problems:

1) Urban legend or not: Running until completely dry will suck up the nasty stuff in your tank.

2) Harm to the fuel pump.

3) Idling efficiency <> driving efficiency. You would need to make sure your car is well-tuned and the idle set properly. If one engine idles at 800 rpms and another at 825 then the test really doesn't work.

I suppose the best test would be to lock the RPMs on a dyno at say 2500 and then just do a MPG test. Even then you would need to make sure you had the same tranny ratios.

Thoughts?
 

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Wouldn't work that well in an EFI system... between the pump, the lines, etc, there is a LOT of fuel in the lines for the amount it takes to idle the car for a while... when the pump loses prime in the tank, it loses pressure across the lines, and you could have a lot of fuel in the lines and the carcould still die.

To realistically do this, it would take a contained pressure vessel, and controlled circumstances.

I'm thinking a tank hung above the engine, with a lin running to the fuel rail. Then, block off the return side of the rail, and pressurize the vessel with enough psi to easily idle the car. btw, the vessel obviously needs to be strong... like maybe a nini air tank or something, or a converted Co2 cylinder that'll take 80psi of air.

That way, when it runs out, it really IS out, and not just losing prime.

Dunno..... just some random ideas. And you probably wouldn't want to let it go dry, but just time it, and measure whats left. If you have a clear vessel, or run clear pressure line looped from top to bottom, you can measure the amount of fuel used over time.

:shrug:
 

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Discussion Starter · #3 ·
Sounds like too much work. :lol: Any MPG is gonna require lots of control. Too much for simple measurements. Looks like a lab is needed.
 

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Charles said:
Sounds like too much work. :lol: Any MPG is gonna require lots of control. Too much for simple measurements. Looks like a lab is needed.
The issue is not what the gas mileage is in the lab, its what the mileage is under REAL driving conditions. That is why what is on the sticker is rarely what you get.
Think about it, hot conditions 90's, AC, bumper to bumper traffic in NYC vs,
70's, AC rarely, mild congestion on the roads in Portland, OR vs running the car on a dyno. All are different and potentially some setups are better on one than the other. That is how the car manufacturers scam the system (fuel efficiency tests) by tuning to tests not to real world conditions.
 

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Discussion Starter · #5 ·
I suppose the closest one can get is to just test one car driven by the same driver over similar weather conditions for about 1000 miles. As we have distinct summer months of constant heat, that's about the best time in Texas to test. I consistently get right at 30-32 mpg all year. So a 10% increase would be needed for me to really notice.

That's why the idle test sounded good. It lasts less than an hour and can be done on days with similar humidity and temperature. It might limit the variances more than driving tests.
 

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edit
I re-read the post and realise now that my response doesn't really apply all that well, Woops, thats what i get for skimming posts. **shrug**
/edit

I constantly measure gas mileage. But I wouldn't want to run empty all the time. Also, IC engines do not like to idle, mainly because it is the least efficient rotational speed range that it can be in. Here is what I do just to keep a relative track of mileage and effiency:
Every time I get fuel I fill the tank up until the nozzle mechanism clicks off. I then keep track of the miles since I last filled and I write it down on the reciept showing the gallons consumed since I last filled her up. THen I reset the trip meter before I drive away.
This way I can see about how many miles I'm getting per 10 gallons give or take. I keep reciepts and average them to get a better number. (I realise the pump shutoff mechanisms are not all the same so that is why i average over many tanks). This is also a good thing to do to see changes in performance of your car. I remember seeing a slight but consistant difference when I lowered my car.
Sometimes people see me calculating the mileage at the gas station and comment that only an engineer could be so meticulous. I swear to them that that is true, but other crx guys/gals do it too!
 

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^I just do it in my head, only a real engineer would do it in his/her head :lol: haha

I went 330 miles composed of highway, interstate and in town driving and put in 8 gallons (I always top her off and by topping her off I mean wait until the gas bubbles out of the tank lol). I was pretty damn happy to average 40+ MPG on that tank. It was on Shell 87 octane. I had recently put air in my tires so I think that helped out too. I have been getting around 35+ MPG in mixed driving before that. This is in a DX auto that is lowered with a hollowed out cat, cat back exhaust and K&N filter. Yes, for those of you who doubt it, I DID get better MPG with the added on mods.

I always keep track of my MPG in my daily driver. It is a good way to make sure she is tuned up. Now only if I had an HF...
 

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Discussion Starter · #8 ·
I am still looking for that mint 88 HF... if any are left.

As you state, fuel efficiency is an indicator of engine health. I brought this up before, but not all gas retailers put the same level of additives in their lower octane as they put in their higher octane gas. Many have actually REDUCED the amount of additives in their lower octane fuels. The following retailers have agreed to the higher standards for all octane levels. I try to always get my gas from one of them:
QuikTrip
Chevron
Conoco
Phillips
76
Shell
Entec Stations
MFA Oil Company
Kwik Trip/Kwik Star
The Somerset Refinery, Inc.
Chevron-Canada
Aloha Petroleum
Tri-Par Oil Company
Shell-Canada
Here's the rub:

TOP TIER Detergent Gasoline is a recently established new standard for gasoline performance. Four of the world's top automakers, BMW, General Motors, Honda, and Toyota recognize that the current EPA minimum detergent requirements do not go far enough to ensure optimal engine performance.

Since the minimum additive performance standards were first established by EPA in 1995, most gasoline marketers have actually reduced the concentration level of detergent additive in their gasoline by up to 50%. As a result, the ability of a vehicle to maintain stringent Tier 2 emission standards have been hampered, leading to engine deposits which can have a big impact on in-use emissions and driver satisfaction.

These automakers have raised the bar. TOP TIER Detergent Gasoline help drivers avoid lower quality gasoline which can leave deposits on critical engine parts, which reduces engine performance. That's something both drivers and automakers want to avoid.
 
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