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Old 08-14-2007, 06:40 PM   #1
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A feel-good FE experience

I rented a Dodge Dakota V8 4x4 to haul some freight to the office from the terminal today. I could have done it with an S10 but the Dakota was all the rental place had available.

So I piled into the truck to drive to the freight terminal and noticed it had a factory trip computer. Flipping around to the MPG display showed 16.2. I drove to the terminal and picked up almost a half ton of freight (the truck squatted down pretty good when the forklift loaded it up!) Drove it to the office (mix of city and interstate), unloaded the freight, and took it back to the rental place -- stopping for a couple gallons of gas and getting caught in an accident-induced traffic jam in the process. Total distance: 57 miles.

When I got out of the truck at the rental place, the trip computer was showing 26.6MPG. And that was with no neutral coasting or, in fact, any techniques beyond gentle driving.

I had a lot of fun thinking about the next renter getting in and watching the readout fall and fall and fall back down to 16 or so MPG and wondering, "What the heck?"

Anyway, nothing scientific about it at all -- I didn't even look to see what mileage the FE was being calculated on -- I just found it a fun experience and thought I'd share.

One thing I noticed during the drive is that the revs were very low -- I could cruise at highway speeds while running under 1500 RPM. (My Cabrio downshifts if I get much below 1600... and 1600 is somewhere around 35MPH.) I've owned four cars in my life and they were all four-bangers, so I have limited experience with big engines. Are low RPMs typical of vehicles with V8s? I would so love to cruise at 1500RPM with an under-2.0L engine!

Rick
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Old 08-14-2007, 07:00 PM   #2
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Quote:
Originally Posted by Rick Rae View Post
I rented a Dodge Dakota V8 4x4 to haul some freight to the office from the terminal today. I could have done it with an S10 but the Dakota was all the rental place had available.

So I piled into the truck to drive to the freight terminal and noticed it had a factory trip computer. Flipping around to the MPG display showed 16.2. I drove to the terminal and picked up almost a half ton of freight (the truck squatted down pretty good when the forklift loaded it up!) Drove it to the office (mix of city and interstate), unloaded the freight, and took it back to the rental place -- stopping for a couple gallons of gas and getting caught in an accident-induced traffic jam in the process. Total distance: 57 miles.

When I got out of the truck at the rental place, the trip computer was showing 26.6MPG. And that was with no neutral coasting or, in fact, any techniques beyond gentle driving.

I had a lot of fun thinking about the next renter getting in and watching the readout fall and fall and fall back down to 16 or so MPG and wondering, "What the heck?"

Anyway, nothing scientific about it at all -- I didn't even look to see what mileage the FE was being calculated on -- I just found it a fun experience and thought I'd share.

One thing I noticed during the drive is that the revs were very low -- I could cruise at highway speeds while running under 1500 RPM. (My Cabrio downshifts if I get much below 1600... and 1600 is somewhere around 35MPH.) I've owned four cars in my life and they were all four-bangers, so I have limited experience with big engines. Are low RPMs typical of vehicles with V8s? I would so love to cruise at 1500RPM with an under-2.0L engine!

Rick
You sir, are a credit to the race! I just hope the MPG display was more accurate that the one I had in my 90 Caddy. It would show I was getting 23MPG, and I'd be all stoked. But when I did the math it amounted to 18-19 MPG!
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Old 08-14-2007, 07:01 PM   #3
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So what was the actual MPG with the fill up? It was probably really close. Good job with such a beast.
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Old 08-14-2007, 07:15 PM   #4
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Originally Posted by Rick Rae View Post
One thing I noticed during the drive is that the revs were very low -- I could cruise at highway speeds while running under 1500 RPM. (My Cabrio downshifts if I get much below 1600... and 1600 is somewhere around 35MPH.) I've owned four cars in my life and they were all four-bangers, so I have limited experience with big engines. Are low RPMs typical of vehicles with V8s? I would so love to cruise at 1500RPM with an under-2.0L engine!

Rick
Yes this is typical with big motors. a 8 cyl motor pops at 1200 rpm what a 4 banger does at 2400. V8 = torque!!! you should have flored it just once from a dead stop. Really bad for FE, but kinda fun to roast the tires. Or better yet, press the brake real hard, then tromp it, and once it gets good and wound up, let off the brake. Then go back and check the nice thick black mark on the road, after the smoke clears that is. Um, sorry I got carried away
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Old 08-14-2007, 07:22 PM   #5
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Thats damn good now ya have to teach my friend to do that (he comes to this site sometimes) he has the same truck and gets maybe 18.
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Old 08-14-2007, 07:36 PM   #6
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So what was the actual MPG with the fill up?
No way to tell. The needle was a bit below 1/2 tank when I rented it and I overshot that on the refill, so I don't know how much I actually burned. Plus I only put in $7 worth, far too little to get any sort of useful reading anyway.

But, if you figure 57 miles and 2.6 gallons (what I drove and what I put in), that's about 22MPG. So, 26.6 isn't out of the question.

Who knows what the previous driver(s) did either; maybe lots of idling or running the A/C hard. But according to the EPA site 16.2 looks pretty reasonable for "typical" driving:

Quote:
V8 M/6 4WD: 14/19 mpg
I wasn't intending to brag -- I don't think I did all that great, really, compared to what some of you guys could pull off. I was merely stoked by how much difference just driving gently, coasting to lights (even in gear), not riding the brakes, etc. could make. My outlook is really changing: I used to think EPA numbers were totally unrealistic and unattainable goals. Lately I'm starting to believe there's no excuse for anyone not at least meeting EPA.

slurp812, thanks for the info on V8s!

Rick
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Old 08-14-2007, 08:03 PM   #7
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Are low RPMs typical of vehicles with V8s? I would so love to cruise at 1500RPM with an under-2.0L engine!
Completely normal -- it's geared to have a close to optimal power output to maintain cruising speed.

If you tried that on a 2.0 that didn't make enough power at cruising speed --- you'd have terrible FE :/ Taller does not necessarily mean better, optimize power output to what's necessary to maintain cruising speed


And that's an impressive number
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Old 08-14-2007, 08:08 PM   #8
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If you tried that on a 2.0 that didn't make enough power at cruising speed --- you'd have terrible FE :/ Taller does not necessarily mean better, optimize power output to what's necessary to maintain cruising speed
Depends on the car. IME just about any car built from the 90s on has suboptimal gearing for efficiently cruising at the speed limit. Instead they having something that'll allow the car to go ~120-200+mph. I think we could see a third less consumption at the usual highway speeds w/ better gearing, but then we couldn't go 100+mph on the street. Recently manufacturers have been going lower again, but I still haven't seen the same ratio of gearing to displacement that was standard on cars after the oil crunch of the 70s.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 08-14-2007, 08:25 PM   #9
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Instead they having something that'll allow the car to go ~120-200+mph. I think we could see a third less consumption at the usual highway speeds w/ better gearing, but then we couldn't go 100+mph on the street.
The gentleman from wrightspeed touched on that point, having those super high top speeds isn't so much a goal, but a engineering by product (goof?) to keep rpms low (for engine longevity, noise, comfort, etc.) at a cruise.

That being said, his electric Atom was geared to top out at 105, but has acceleration like you wouldn't believe: 0-60 in 3.07 seconds is too fast to even piss your pants (I can say this first hand).

The big drawback of having such low gearing is life expectancy. A small engine at full output won't last as long as a bigger engine living at low output :/ This is why we can expect 3,000-5,000 hours+ out of an automobile gasser.
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Old 08-14-2007, 08:44 PM   #10
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The big drawback of having such low gearing is life expectancy. A small engine at full output won't last as long as a bigger engine living at low output :/ This is why we can expect 3,000-5,000 hours+ out of an automobile gasser.
Edit-Well.. yeah, a bigger engine versus a smaller at the same output is a given. What about the same sized engine at different levels of torque versus speed?
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