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PostPosted: Mon Jul 07, 2008 1:09 pm 
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Joined: Tue Apr 29, 2008 8:06 pm
Posts: 1445
Location: Atlanta GA 30052
there is no fuel saving
reasoning:
3cyl goes 60mph at 3000 rpm = 1/2 max = 25hp
but more hp (by turning off lights) is not needed. lights drop hp from 50 to 49.5. there is no fuel saving b/c the engine still turns 3000 rpm using 25hp. same mpg.

hp from 50 to 49.5 is explained at
viewtopic.php?f=29&t=38636

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daily driver: red 1991 Metro 3cyl 5sp, roof rack, 8 degree advance,
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PostPosted: Mon Jul 07, 2008 1:51 pm 
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Sad but True...

Joined: Fri Jul 27, 2007 8:20 pm
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Location: Saskatchewan
who cares anymore, do it cuz you want the lights off during the day

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PostPosted: Tue Jul 08, 2008 6:39 am 
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Bozo the crying clown

Joined: Tue Mar 13, 2007 9:19 am
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Location: Chester County PA
Good post, man. :-)

Jimmy


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PostPosted: Tue Jul 08, 2008 8:04 am 
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Joined: Sun Sep 02, 2001 11:55 am
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Location: Calgary, Alberta
you're right that most of us are not likely to see a difference travelling the highways at 120km/h-75mph... but at 50km/h -30mph rolling resistance is 1hp and aero loss is only around 1 hp (+ trans losses if the person is in gear)... an extreme hypermiler in pulse and glide or whatever, may see some kind of improvement at low speeds.

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PostPosted: Wed Jul 09, 2008 8:56 am 
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Joined: Tue Mar 16, 2004 6:23 am
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I disagree completely. If it takes 25 hp to drive the car forward, it takes 25.5 hp to drive the car and generate the electricity for the lights.

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PostPosted: Wed Jul 09, 2008 9:48 am 
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Location: Surrey, BC CANADA
I believe any load on the engine be it an alternator drag or extra weight in the car, will affect mileage as well as power on any car.
It is in my opinion proprtional to the size and power of the engine, plus weight of the car to whether it is measurable or not.
I bet if you tracked mileage over a year in each case, being that the only variance is the lights being on or off.
You would notice a loss in mileage and power, but its not likely any one can do that.
But it is not worth the fuss, as its safer to have the lights on nowadays.
This is why its law to have DRL's.

You can also get better mileage if!
you go on a diet!
don't drive with anything or anyone else in the car!
and drive naked! :razz: Less wind resistance. :D

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PostPosted: Thu Jul 10, 2008 12:09 pm 
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Joined: Thu Jun 05, 2008 5:13 pm
Posts: 22
Location: Brentwood, CA
xrw44 wrote:
there is no fuel saving
reasoning:
3cyl goes 60mph at 3000 rpm = 1/2 max = 25hp
but more hp (by turning off lights) is not needed. lights drop hp from 50 to 49.5. there is no fuel saving b/c the engine still turns 3000 rpm using 25hp. same mpg.


I disagree as well, ther is a misconception by many when it comes to a car's electrical system. Here's my atempt to explain it in simple terms that even I understand:

Think of your car's battery as a storage tank of water, a water tower if you will. I takes work to fill the water tank, but gavity helps it flow out, all we need to do is open the spigot. Every electrical load you place the car under, draws water from the tank, like opening the spigot. No electrical load at all means the spigot is closed. Turn on every electrical devise, and the spigot is wide open. Open that spigot wide open, and the water level goes down over a short time. With no electrical device in use, the spigot stays closed. Got it so far? Good. Well, the smart engineers who designed your car, want to keep the water tank (battery) full, so there is some reserves built up that allow one to say, start the car when it's 10 below outside.

Now, the alternator's purpose, is to regulate the inflow of new water to that tank, to keep that water tank topped off and full. If the water tank is at capacity and full, the regulator says "No thanks, I don't need or have a place to store any more water, please turn off the pump"

It takes work to pump 'new water' up into the water tank, to replenish what you have used. Work requires fuel, in this case gasoline. Weather idling, or traveling at 3000rpm, if the alternator is charging to replenish electricty being used, you must be using more fuel.

So, what if you disconnected the alternator, disable the ability to replenish that used up electricy? In that case, you would not use any more fuel to run your headlights, stereo, or GPS. But, you drain the battery and might get stuck. Also, run like that for very long, and the coil refuses to spark and the engine dies out on the hiway.


anyhow, i hope that helps


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PostPosted: Thu Jul 10, 2008 12:22 pm 
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Sad but True...

Joined: Fri Jul 27, 2007 8:20 pm
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Location: Saskatchewan
you didnt say anything we didnt know already. its a very very minimal effect at best, and some places its illegal to disable them (not 100% on this).

but how about this, if you just drive your car on short trips, throw a dry cell battery in there (optima red/blue/yellow top) and disconnect the power wire off the alternator and wrap it (so it doesnt have hot power from the battery to ground out to the motor) and drive around and plug your car in overnight to charge it back up.

guaranteed from a good battery youll get 3-4 starts + 40-50km out of a full charge before you start to kill anything. keep the revs down as much as possible to save power from the spark electricity.

theres your mpg gain (note this post wasnt totally serious, but theres also no reason it wont work)

I know when I hit 1100rms hard each time, I can FEEL the car slow down at almost any rpm. thats like full alternator duty when it hits hard. THAT has to affect mpg's, having <10watts on will not make any noticable difference. the wind plays a bigger factor than that

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1991 Swift GT Build G10 +25 psi + other goodies
1996 Metro Build QR25de swap, still undecided where to take it
the lolcar family


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