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Old 02-17-2007, 06:32 AM   #21
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Just a thought, A carbureted car very likely would still spew fuel into the engine when coasting with in-gear coasting with the ignition off , and make a nice backfire when you turned it back on
My dad said he used to blow up mufflers when he was a kid by doing this.
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Old 02-17-2007, 06:45 AM   #22
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I blew up my share of mufflers back in the day. I used to do that all the time. I found out that a regular glass pack would not blow up the way a regular mufflers did. I was pretty disappointed when I got my first FI vehicle, no more BANG!
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Old 02-17-2007, 07:10 AM   #23
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Not to be mean but it's obvious that you would get better FE when coasting down a hill with the engine off. Thats just common sense.

The only test that would have been almost worth while would be coasting in Neutral with engine on, and coasting in gear with engine on.

Rather then that if you thought you wouldn't get better milieage with coasting in N with the engine off there is something wrong.
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Old 02-17-2007, 08:01 AM   #24
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I use the SG for measuring improvement over different segments and the hand calcs when topping off the tank as the final word
Thats all i've been using it for. just to compare diff situations. not for absolute numbers. thats why i don't post in the daily updates thread any longer. my last tank was showing just under 30 on the SG but when i refuled was almost 32.
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Old 02-17-2007, 08:25 AM   #25
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Not to be mean but it's obvious that you would get better FE when coasting down a hill with the engine off. Thats just common sense.

The only test that would have been almost worth while would be coasting in Neutral with engine on, and coasting in gear with engine on.

Rather then that if you thought you wouldn't get better milieage with coasting in N with the engine off there is something wrong.
The thing is there's some controversy about weather or not it is WISE to coast down a hill in neutral and/or with the engine off. So some measure of exactly what the benefits of each permutation are can be helpful in aiding people to make their own decisions.

Yes it is obvious that you will coast farther down hill in neutral vs with engine braking, and that not burning gas while moving is infinately better than burning gas.
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Old 02-17-2007, 09:22 AM   #26
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Therefore the mpg to get back to the spot where test one ended =
(8.7mi - 5.1mi)/(.2581 - .2161) = 85.7mpg for 3.6 miles (uphill)?
If his car was slowing down to 30mph while rolling in neutral along these 3.6 miles, it would have to be a very very shallow hill at that point. Perhaps virtually level or even a slight incline? So the FE on the first part of that return trip would be pretty good. I agree that 85 seems odd but with his degree of aero mods, the mileage under these conditions should be wuite good.

I think the best way to run this test would be to do the neutral coast first. Mark where the car falls below 30mph and then on the engine-off, in-gear test, restart the engine and continue driving to the point where the neutral coast ended (but at what speed???).
I would be interested in seeing fuel used numbers at the turnaround point and back at the start, as well as distances to both the turnaround point and where the in-gear test needed the engine restarted.

Regarding fuel use when coasting in gear with the engine running, I think alot of mileage computers aren't going to calculate that right. Especially on newer cars that shut off injection during coasting and you would get a divide by zero error. If the programming is done 'right' and the computer just logs miles traveled divided by gallons used based on injector pulse width then the average mpg should stay right, but instant mpg would be limited by however the computer gets around a potential divide by zero error. Kinda disappointing that the scangauge defaults to a 0.1gal/hr fuel use reading.
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Old 02-17-2007, 09:52 AM   #27
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skewbe -

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Originally Posted by skewbe View Post
The thing is there's some controversy about weather or not it is WISE to coast down a hill in neutral and/or with the engine off. So some measure of exactly what the benefits of each permutation are can be helpful in aiding people to make their own decisions.

Yes it is obvious that you will coast farther down hill in neutral vs with engine braking, and that not burning gas while moving is infinately better than burning gas.
For me, the only question is whether I can get a "free brake" + hydraulics with the engine off/in gear/downhill. I know it will slow me down, but my traffic density is so dangerous that I don't have many spots where I feel safe enough to coast downhill/engine off/in neutral. I need my brakes and steering on the 710 going South because the semis are taking crap to and from the Long Beach Harbor (literally by the boatload).

Any time the tire rolls forward with no gas to the engine is an MPG benefit, period.

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Old 02-17-2007, 09:57 AM   #28
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Yah, on some cars (i.e. mine, apples if you like) the scangauge reports base fuel consumption during overrun/EOC in gear, even there isn't any, which is not a big deal IMHO.

CO reported zero fuel used at the end of his first test leg so I assume his doesn't do that.

Just a thought, A carbureted car very likely would still spew fuel into the engine when coasting with in-gear coasting with the ignition off , and make a nice backfire when you turned it back on
In my second ill-fated Karmann-Ghia (the one I don't like to talk about), the engine was so bad that when I floored it, the 4 CONICAL shaped exhaust tips on my muffler would make a righteous explosion from unburned gas. Looked great at night, just like the 4th of July.

I keep looking for that muffler in the Hot VWs mag, but I can't find it. Must have gone out of business. Best sounding VW muffler EVER!

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Old 02-17-2007, 10:19 AM   #29
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I agree: bike!

So how's the braking with engine off, on the second or third application? does the car have ABS?
Food energy to travel the same distance on a bike will cost more than gas going the same distance.
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Old 02-17-2007, 10:28 AM   #30
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The test is correct giving EOC in neutral higher mileage for more distance since the EOC in gear added drag and reduced the distance traveled. It does not matter that the total distance for each test was different but in fact IS the point with coasting in neutral . . . you go further and thus increase the average MPG. HOWEVER, if you wanted to use less gas, then traveling the same distance would be a factor or at least turning around at high speed to go back up the hill coasting with engine off would still result in less gas used also. Braking is pointless and would make the results the same as you would simply be going up a hill the same distance.
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