RE: 17% mpg increase no mods needed

Subject: RE: 17% mpg increase no mods needed
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optimum is just fast enough to lock up the torque converter of fast enough to run in 5th without lugging. 60 is way too fast for best fuel economy as it takes 1.7X the HP to run at 60 as it does at 45. were you aware that if you run at 50 and then at 100 it takes 4 times the power to runat 100 then 50? the general ratio is 4 times the power for 2X the speed.

N56629
Dodge Dakota
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9/06/2005
19:25:00

RE: 17% mpg increase no mods needed
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That must mean that the engine is more efficient at 100 than at 50 because you sure don't use 4 times as much fuel. I'm not sure that you would even use twice as much fuel. Your figure of four times the hp for no more than twice as much fuel sounds pretty good.

In reality it's not all that simple.

ObieWonDakota
Dodge Dakota
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9/06/2005
20:35:09

RE: 17% mpg increase no mods needed
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Been tracking my mileage ever since I bought my used '01 Dak with 32K on the engine. Same route to work everyday, 30 miles each way with 22 miles interstate at 65mph (cruise) and remaining 8 miles country roads doing 55mph with only 3 stoplights/signs on those roads. Consistently averaged 18.5 mpg.

Took a trip to South Carolina the other weekend. Went I-75S to I-40E to I-26E, which is very hilly especially going through the Gorge on I-40. To keep up with traffic, mainly drove at 75mph and upwards of 80mph at times. A/C was on half of the trip. On the way there, I got 19.8 mpg and on the way back (same type of driving), I got 20.1 mpg. I would love to do that same trip at 65 mph to see if there was any difference, but keeping up with the flow of traffic is a lot safer.

I did put a drop in K&N filter in before the trip. I'm assuming (not a good thing to assume I know) that the filter was the difference, but then again, I've made that trip before at those speeds and still got close to that same type of mpg. I'll track the next couple of weeks into work and back and see what it gets. Trying to just keep the Dak parked when I come home and use the wife's car for other errands so the computation will be accurate. I'll keep you posted, but for me, it seems you get better mpg at a CONSISTENT higher speed, but I'm not an engineer so it's just a guess from what I've experienced. BTW, 82K on the Dak.

ObieWonDakota
Dodge Dakota
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9/06/2005
20:36:48

RE: 17% mpg increase no mods needed
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And sorry for that. I thought I was in the V-8 board and now realized it was the V-6...DOH!! Anyway. all that above was the the 4.7 V-8.

prodak
Dodge Dakota
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9/06/2005
23:19:22

RE: 17% mpg increase no mods needed
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To 'uh GB 2000'-
Coefficient of drag is proportional to velocity squared, however, aerodynamic drag isn't consuming 100% of your fuel (not even at 100mph).

prodak
Dodge Dakota
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9/07/2005
00:06:06

RE: 17% mpg increase no mods needed
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Some of you may be shocked to learn that average efficiency of internal combustion engines is about 30%. That means that roughly two-thirds of your gas goes to waste heat, friction and pumping losses - and that's before you even get to the tranny. At highway speeds much of what's left goes to overcoming drag, but that's probably less than 20% of the gas you put in the tank.

Dan M
Dodge Dakota
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9/07/2005
05:23:49

RE: 17% mpg increase no mods needed
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Since I adjusted the low/reverse band in my transmission and replaced the fluid and filter I have calculated that I'm getting ~20mpg. up from ~18 (17.5-18.5). I will have final numbers when I fill up this weekend.

- Dan M

schmidtmike
Dodge Dakota
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9/08/2005
23:16:26

RE: 17% mpg increase no mods needed
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Back to the efficiency thing. Chrysler made the Patriot Trans Am car back in 1994. It utilized a gas turbine engine with a heat containment system that gave the car 55% efficiency. In turn, the car produced 800hp, and managed 80mpg in a test similar to the EPA mileage test. But, the car never saw production, because the exhaust developed over 1700 degrees at the tailpipe, and melted vehicles behind it.

modain
GenIII

9/09/2005
05:12:15

RE: 17% mpg increase no mods needed
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That exhaust feature would be great to use when faced with idiots on the road. Instead of wishing for a rocket launcher, just get in front of them and "gas it". :-)

=========================================
2002 Graphite QC SLT Plus, 4.7L, NV3500, Superchips 3715, 3.92 LSD, loads o'fun...
2001 Patriot Blue Durango SLT, 4.7L, 45RFE, Superchips 3715, 3.55 Open (for now)

Dan M
Dodge Dakota
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9/09/2005
06:17:27

RE: 17% mpg increase no mods needed
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A Chrysler T/A???

- Dan m

Bob Lincoln
Dodge Dakota
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9/09/2005
08:29:02

RE: 17% mpg increase no mods needed
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"That must mean that the engine is more efficient at 100 than at 50 because you sure don't use 4 times as much fuel. I'm not sure that you would even use twice as much fuel. Your figure of four times the hp for no more than twice as much fuel sounds pretty good.

In reality it's not all that simple."

That's not what he meant. The kinetic energy required to move the vehicle is proportional to velocity squared (K=1/2 times Mass times Velocity times Velocity). So you double your velocity, and it requires 4 times the energy to move you.

Most vehicles only need about 20 hp to maintain a speed of 65 mph on level ground. If you never needed reasonable acceleration, you could actually run a 50 hp motor in most cars. But we like 100-200+ hp so we can get out of our own way.

Since you only need 20 hp or less, feathering the throttle and going slower than highway speeds will give you maximum gas mileage. So uh GB 2000? is correct, go just fast enough in high gear not to lug the engine, and there's your peak gas mileage.

prodak
Dodge Dakota
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9/09/2005
09:57:29

RE: 17% mpg increase no mods needed
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Bob, as I already stated, aerodynamic drag coefficient is proportional to velocity squared - total energy required to move the vehicle is determined by drag PLUS engine losses, drivetrain losses, and rolling resistance. Not sure what you mean by "kinetic energy required to move the vehicle..." (yes I know what the word kinetic means).

prodak
Dodge Dakota
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9/09/2005
13:35:43

RE: 17% mpg increase no mods needed
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Bob, Google turns up the following definition for "kinetic energy":

The energy possessed by a body because of its motion, equal to one half the mass of the body times the square of its speed.

Your formula is correct, but what does it have to do with energy consumed, that is, energy required to produce motion?
"uh GB 2000?" introduced horsepower into a discussion about fuel efficiency, and there are countless variables that determine how one relates to the other. Remember, HP is a measure of the engine's energy output exclusive of its energy input - which in this case is gasoline.

Dan M
Dodge Dakota
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9/10/2005
07:41:55

RE: 17% mpg increase no mods needed
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Driving at my normal speeds after adjusting the transmission, I'm now up to 19 mpg combined.

- Dan M

Rene
Dodge Dakota
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9/10/2005
11:23:24

RE: 17% mpg increase no mods needed
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I have a 2003 Quad Cab. We have some down hills here in PR that goes up to 3 miles long.
How bad is it for an automatic transmission if I shift it to neutral and at the end of the hill back to drive?

Your comments are appreciate!!

This gas pricing is taking a toll on me.

hum
Dodge Dakota
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9/10/2005
12:39:48

RE: 17% mpg increase no mods needed
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you are better off to leave it in drive. Less wear on the drive train and it keeps the fluid pumping through the cooler.

N56629
Dodge Dakota
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9/11/2005
08:27:50

RE: 17% mpg increase no mods needed
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If you are on a steep hill you will just end up using your brakes more which in some cases could be dangerous. I also doubt that you are using that much more fuel even though you are turning higher rpm's. In either case the throttle plates are closed. In the idle position you are burning about .5-.6 gallons per hour.

Rene
Dodge Dakota
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9/12/2005
08:34:50

RE: 17% mpg increase no mods needed
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Thanks for the inputs.

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