Hi, in relation to gas engines only, the best fuel economy would be at the highest vacuum reading and in the highest gear in relation to speed.
What I'm saying is that the best fuel economy is with the lowest vacuum. I think if you actually hooked a vacuum gauge up to your vehicle as you drove you would see that the highest gear ALWAYS gives you the lowest vacuum. Remember that like all good experiments you must only vary the one parameter you are testing for. So same speed, same grade, same temperature and wind directions. Just set cruise control and start shifting. Try it at different speeds.
I humbly ask that the line in bold above be established as fact until somebody states that they have personally performed this test and recieved contrary results. It would be much appreciated if somebody actually does this test so they we can move forward from this point and this can be established as fact based on more than just my integrity, which I'll admit is quite weak from your perspective.
I had a Ford Excursion with the Triton V-10. Complete piece of junk. It blew up and Henry wouldn't cover it. No more FoMoCo for me, ever.
I have a Dodge Ram 2500 4x4 long bed quad cab and Cummins. All I do is change oil and drive. No problems at all. Ever.
I also subscribe to "Diesel Power" magazine. Dodge is indeed bringing out a diesel version of the Power Wagon. The review on it was awesome. A real piece of machinery!
The Hemi with the cylinder DeAct is an excellent engine. More power to you with it. (I plan to get a Challenger with that engine) But don't discount the Cummins. It is the only real diesel in a pickup truck out there. It is a true "Medium Duty" engine. I know many people who have owned them. They all say the same thing. Change the oil, put in fuel, and turn the key. That's it. That has been my experience for the past four years.
I pull a 34' Avion that weighs 9600lbs and I can accelerate up any hill I've ever encountered, including the great Smokies. I recently went up a hill in PA that was nearly 15% with a 15mph hairpin turn. I went from 15mph to 60mph in a half mile. The Cummins is a great mill. Period.
OK, off my soapbox
But seriously, you look in Diesel Power at the trucks that run 10 second quarter miles, and there are ten Cummins to any other brand. There's a reason for that. They are stout.
Here's the deal: Best economy results when your air to fuel ratio is approximately 14.7 to 1
Best horsepower results when your air to fuel ratio is approximately
12.0 to 1.
As you can see, you need to run a bit rich for best power. You lean it out for best economy.
With a carb, you're stuck running a bit rich. With EFI, the computer should take care of this for you.
In general, an engine is a pump. And whether you have a V8 or a turobocharged 4-cylinder, it takes a certain amount of fuel to produce a certain amount of horsepower. There won't be a huge difference. A V8 has a little more internal friction than a 4-banger, but it's not that much.
That's why a modern Chrysler 300 with cylinder Deact can get 28mpg, yet still give you 350hp when you tromp on the loud pedal.
My wife's old Crown Victoria (soon to be replaced by MoPar) will routinely deliver 26-27 mpg on the highway when cruising at 80 mph simply due to the fact that it only requires X horsepower to go that fast, whether it be from a 4 or an 8. Aerodynamics and weight mean more than the number of cylinders... Power required = fuel burn regardless of configuration.
What I'm saying is that the best fuel economy is with the lowest vacuum. I think if you actually hooked a vacuum gauge up to your vehicle as you drove you would see that the highest gear ALWAYS gives you the lowest vacuum. ...
Not every engine has vacuum at the intake manifold.
'specially the turbo'd engines
For the rest of them... wouldn't you want more vacuum? Or are we saying the same thing. My old Willy's had vacuum powered wipers & defroster which would go like the Dickens at a stop light, but would just about shut off if you tromped the power. In general, the trick is to drive using the least amount of power necessary to get the speed you want.
Actual formulas are pretty involved, I'd guess, although I haven't really done more than just think about it. Have read in a trade journal that 100-200 RPM either side of the peak torque spot is a good place to shoot for, both in steady state and during acceleration. That seems reasonable to me. Of course that number can be hard to pin down.
Not every engine has vacuum at the intake manifold.
'specially the turbo'd engines
I'd like to keep the analysis to naturally aspirated spark ignited gasoline fueled reciprocating four stroke engines. This is proving complicated enough.
I originally brought up the pumping loss thinking that people would recognize right away what it is. I gave the example of how automakers are taking this seriously, I've made some predictions that people can test, such as that a diesel engine inherently has no engine braking, and that vacuum goes down when you shift up. This is proving to be a rather ominous task, getting people to put together what they know, and what they don't know, in the correct way to draw the correct conclusions.
I'll present another way to test the pumping loss: If you have a standard transmission, when your in some gear at high rpm simply release the throttle. That's the pistons trying to suck down on the intake stroke against the vacuum in the manifold. Please read a few posts back.
As far as people asking for equations: The pumping loss is basically [vacuum]*[displacement]*[rpm]
It's actually a little bigger because the vacuum on the pistons is a little higher because of the resistance of the valves. This is exactly the same as the exhaust pumping loss, replace vacuum with exhaust manifold pressure.
I recieved a private message from a forum member that was of a technical nature. I asked that he post it here for all to discuss, but he refused saying that I am being political. I assure you that what I am telling you is fact, and that it's very difficult to have a debate politely when fact is on your side.
Hi, some cars several years back had what they called an "Economy Gauge" It was just a vacuum gauge with green, yellow, and red on the face. Green being the highest vacuum reading and the best economy. Once again the best economy would be at the highest vacuum acheived in any given gear. Also, our supercharged Thunderbird had a Vacuum/Pressure gauge that showed vacuum until you gave it heavy throttle, of course, and then read pressure from the blower. As for your "Prediction" it is already a known fact that Diesels don't have any engine braking; That's why they made Jake Brakes.
Hi, it sounds good, but peak torque is not the best place for economy. At freeway speeds most gas engines are running at about 1800 to 2200 RPM. When does your engine get it's peak torque? My Navigator gets it's peak torque at a very low 2750 RPM, but most gas engines get their peak torque well above 4,000 RPM; That would put you at well over 100 MPH or more. Does that make sense that your best gas mileage would be at that speed? I don't think so!
After nearly 20,000 miles of towing our Safari 25 FB/SE around our beautiful country with our 2005 Ford PSD FX4 Crew Cab long bed, we said goodbye to the diesel and bought a 2008 Dodge Power Wagon with a Hemi gasser.
Why you ask, who would be stupid enough to go from an ultimate tow machine to a gasser?
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I am ready for the flaming.
I deleted the meat of the origional post quote to reply to the point of the thread. Timemachine did the smart thing. He got rid of a lemon and bought something he hopes is better. I hope he gets many years of good service from the new rig.
From my point of view his logic sounds great!
Diesel has it's place in long distance, I heard over 25,000 miles per year, and heavy loads, you define a heavy load for yourself. USA Today had an article of a study that indicated that diesel was more efficient than hybrids or gas for energy efficiency. It would not matter what you had if it was a lemon.
A tank of stabilized diesel should last longer in storage than gas. When the poo hits the fan, like it is now, I want to be ready for a supply interruption.
We have both gas and diesel vehicles and a big tank of fuel oil in an energy emergency.
By all means get rid of lemons, make lemonade.
__________________
Robert
"Talk is cheap, Airstreams are expensive," Wally Byam.
Buy in haste, repent at leisure; been there, done that.
"You cannot rush quality," fastRob.
I assure you that what I am telling you is fact, and that it's very difficult to have a debate politely when fact is on your side.
Having facts on your side is meaningless if your audience cannot interpret the facts. Your seeming unwillingness to offer more details to your position naturally leads others to be less than enthusiastic in a conversation.
I could say "because 2x = 4, x = 2" all day long, but at some point I would have to explain it in greater detail other than "That's a fact" (Geez, I hope it really is a fact!).
You may be better served by saying what you mean and providing some detailed explanation rather than providing us open-ended questions that so we can figure it all out. People are thinking about your posts, but not from the same reference that you present your information. Some of us just don't quite put it together like you do, and our best efforts to understand fall a little short.
I also agree it's time for a different thread to have a meaningful discussion about some interesting information. Believe me.. I am all for understanding how to improve efficiency from our current 8 to 10 mpg in tow (we don't tow with the usual vehicles). If I could get to 12 mpg in tow, I'd feel at least 20% smarter.
Briefly, I have the 2007 Dodge 6.7L Diesel. In Los Angeles traffic I'm getting 17.5 mpg. Just finished a trip down to San Diego, CA. It has a few small hills on the way and back. I got 15.8 mpg.
Just saying......
__________________ "Better to have more then you need, then need more then you have because you don't have enough!" AIR #: 8129
the last 35 or so posts in this thread have been very weird.
blah blah blah
Weird! WEIRD! Who you calling weird??
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Hi, some cars several years back had what they called an "Economy Gauge" It was just a vacuum gauge with green, yellow, and red on the face. Green being the highest vacuum reading and the best economy.
These gauges really measure the load on the engine, and yes, the load affects the fuel economy. It takes more fuel to make 100HP than it does to make 50HP. I'm talking about the engine using the least fuel to produce a given horsepower. I've seen these gauges as well, and while the overall fuel consumption is going up because the power you are producing is going up, the specific fuel consumption in gallons of fuel per horsepower-hour is going down.
I am not talking about the fuel economy of vehicle as a whole. You're driving conditions determine how much power you need at the rear wheels. I am saying that the most efficient way to make that power is to gear the engine such that it is at full throttle.
So if eliminating the pumping loss doesn't improve fuel economy, then what is it that improves the fuel economy of these multidisplacement engines? I'm glad we have a lot of experts here, this should be answered quickly, and I can learn something new.
Quote:
Originally Posted by ROBERTSUNRUS
As for your "Prediction" it is already a known fact that Diesels don't have any engine braking; That's why they made Jake Brakes.
Do you now understand why though? I'd like to point out that I never actually new that diesels lacking engine braking. The only difference between a diesel engine and a gasoline engine in braking mode is the intake pumping loss.
I also agree it's time for a different thread to have a meaningful discussion about some interesting information. Believe me.. I am all for understanding how to improve efficiency from our current 8 to 10 mpg in tow (we don't tow with the usual vehicles). If I could get to 12 mpg in tow, I'd feel at least 20% smarter.
If somebody starts the thread, I'll participate. Otherwise, I agree, it's best to leave it to rest if people aren't interested.
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Hi, in relation to gas engines only, the best fuel economy would be at the highest vacuum reading and in the highest gear in relation to speed.
