- #36
skeptic2
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- 59
Cyrus said:The drag at low speeds is very small.
I thought we were talking about comparing gas mileage while going the same speed but in different gears.
Cyrus said:The drag at low speeds is very small.
Cyrus said:The drag at low speeds is very small.
PA32R said:
A plot of the comparative contribution of rolling resistance and aerodynamic drag at 0 to 40 meters/second (about 90 m.p.h.) for my vehicle. Note that this only shows the percentage of total external resistive force contributed by each component, i.e., it doesn't show absolute numbers. But it's easily seen that at low speeds almost all resistance is from the tires.
For my vehicle, the two resistive forces are equal (i.e., the curves cross) at about 50 m.p.h.
skeptic2 said:I thought we were talking about comparing gas mileage while going the same speed but in different gears.
skeptic2 said:I thought we were talking about comparing gas mileage while going the same speed but in different gears.
Just to clarify, when you say "rolling resistance", is that where the tires meet the ground only or does it include all drive losses?PA32R said:
A plot of the comparative contribution of rolling resistance and aerodynamic drag at 0 to 40 meters/second (about 90 m.p.h.) for my vehicle.
Cyrus said:It's amazing what's contained inside of books...
http://img8.imageshack.us/img8/396/curvem.png
Every one done speculating? Scanned for his and her pleasure.
Pythagorean said:does this just apply to an non-computerized standard gasoline engine or what?
It could be very different. Modern computer-controlled engines can be programmed to do all kinds of neat tricks. Shortly after I bought my Softail, I ordered a custom exhaust (better scavenging, but not excessively loud), a custom air filter (less restriction) AND I ordered a Power Commander. That's a programmable plug-in computer that can tweak all kinds of things for you. You can tweak the bike for optimum mileage, optimum torque under load, and all kinds of other things that you want. You specify the custom equipment that you have, and choose from a variety of maps. You might want maximum torque under load for 2-up riding, you might want a broader power-band, or perhaps the best fuel economy. That last one is a big deal when you are riding a Sportster through long rural rides with no gas stations. Their fuel tanks are kind of puny.Cyrus said:Why would it be any different?
turbo-1 said:It could be very different. Modern computer-controlled engines can be programmed to do all kinds of neat tricks. Shortly after I bought my Softail, I ordered a custom exhaust (better scavenging, but not excessively loud), a custom air filter (less restriction) AND I ordered a Power Commander. That's a programmable plug-in computer that can tweak all kinds of things for you. You can tweak the bike for optimum mileage, optimum torque under load, and all kinds of other things that you want. You specify the custom equipment that you have, and choose from a variety of maps. You might want maximum torque under load for 2-up riding, you might want a broader power-band, or perhaps the best fuel economy. That last one is a big deal when you are riding a Sportster through long rural rides with no gas stations. Their fuel tanks are kind of puny.
It does change the chart, though. You can increase or reduce fuel consumption at a given RPM by loading the map you want. The module also controls the advance of the electronic ignition. You have to be a good troubleshooter to use them properly, including knowing how to properly shut down at speed, coast to a stop and "read" your plugs. It's easy with fuel injection to create either excessively rich or lean conditions, neither of which are desirable. Of course, you could do that with carbs, too, with improper jetting and adjustment, but these plug-in modules make it easy for newbies to screw up their bikes.Cyrus said:I don't see how reporgramming your engine fuel module changes the chart one bit. All you do is choose to follow a different curve from the one that says 'optimal'.
That chart says for a given pressure and RPM, the engine needs x amount of fuel to operate. Reprogramming it won't change that fact.
turbo-1 said:It does change the chart, though. You can increase or reduce fuel consumption at a given RPM by loading the map you want. The module also controls the advance of the electronic ignition. You have to be a good troubleshooter to use them properly, including knowing how to properly shut down at speed, coast to a stop and "read" your plugs. It's easy with fuel injection to create either excessively rich or lean conditions, neither of which are desirable. Of course, you could do that with carbs, too, with improper jetting and adjustment, but these plug-in modules make it easy for newbies to screw up their bikes.
Ask a mechanic, Cy. The maps are available to change all kinds of performance/efficiency parameters. I bought the module because I understand ICE technology and how to troubleshoot them, and I didn't want to pay the H-D place hundreds to reprogram the stock module every time I wanted to try something different. You can change a LOT of stuff within the design parameters of the engine. Change fuel flow at certain RPMs and you have changed consumption. Change EI advance, and you have changed some more parameters. Did you know that modern cars are fitted with throttle-position sensors? That's so the computer will know the difference between the acceleration you are demanding (with the accelerator pedal) and what you are getting, so it will (according to the map) adjust fuel flow and ignition timing accordingly. For instance, your ignition timing might be advanced during hard acceleration and retarded somewhat when you are cruising at-speed. There's nothing sacred about that chart, though it is a nice graphic on how your automatic transmission should shift to optimize fuel economy.Cyrus said:I don't understand what you mean by 'loading the map you want'. The map decribes a physical system. For x RPM and x PSI you NEED y fuel flow. You can't simply 'load a new map' and magically change this value. It's inherent to the engine itself. The only way to change the map would be to physically modify your engine.
Why don't I simply load a map that has no fuel flow ever and be done with it? -because that's nonphysical.
turbo-1 said:Ask a mechanic, Cy. The maps are available to change all kinds of performance/efficiency parameters. I bought the module because I understand ICE technology and how to troubleshoot them, and I didn't want to pay the H-D place hundreds to reprogram the stock module every time I wanted to try something different. You can change a LOT of stuff within the design parameters of the engine. Change fuel flow at certain RPMs and you have changed consumption. Change EI advance, and you have changed some more parameters. Did you know that modern cars are fitted with throttle-position sensors? That's so the computer will know the difference between the acceleration you are demanding (with the accelerator pedal) and what you are getting, so it will (according to the map) adjust fuel flow and ignition timing accordingly. For instance, your ignition timing might be advanced during hard acceleration and retarded somewhat when you are cruising at-speed. There's nothing sacred about that chart, though it is a nice graphic on how your automatic transmission should shift to optimize fuel economy.
turbo-1 said:You're missing the point, Cy. You can easily run engines over-rich or over-lean at any RPM (with possible detrimental effects to fuel-consumption and/or engine life). The idea that an engine MUST consume a certain amount of fuel at a certain RPM regardless of load, ignition timing, etc is a gross over-simplification. I've been tweaking ICEs for about 40 years now. If you don't believe me, ask a mechanic.
When I bought my old Wide-Glide, I was getting about 40-45 mpg. After fitting it with better-scavenging pipes, low-restriction air filter, high-flow petcock and filter, and rebuilding the S&S Super E racing carb with a Yost Power-tube for improved atomization, I could get 50+ mpg riding through the mountains 2-up, and the bike ran like a scalded cat. Many of the parameters that I had to adjust manually on that bike can be tweaked through mapping control modules these days. BTW, getting reasonable low-speed performance out of a large-bore butterfly carb is somewhat of an art, which is why you see many older modded H-Ds smoking on acceleration at low RPM. Air-speed across the main-jet venturi is insufficient to atomize the fuel properly, so it is not burned completely. Nothing wrong with the design - just poor skills on the part of the person who tuned the bike and thinks that oversized jets are the answer for performance gain.
It is NOT something you would want to turn off, Russ. You still want variable ignition timing (not the old vacuum advance type), but the sweet part of the Power Commander is that you can change the slope of that timing advance to optimize acceleration or perhaps to sacrifice some performance for fuel efficiency. Unless you really want to dig into the maps, and figure out what's going on, the tweaking of the ignition timing is hidden from the user. You are faced with choices like what kinds of performance, economy, etc you want at what loads and rpms, and the web-site suggests maps that might help you get there, based on what kinds of modifications you might have made to the bike. There are tons of maps, tailored to specific combinations of exhausts, intakes, etc. It might take a few tries to get the responsiveness, torque, etc you're looking for and it's a hell of a lot cheaper to program your own module than to run back to H-D and fork over $$$ to remap your stock module.russ_watters said:I would think that variable ignition timing would be a good way to improve performance and change that map. Still, I don't think it is something you would want to turn on and off. If you can get better performance, why turn it off?
It can be very different, Pythagorean. The firing angle can affect the efficiency tremendously, and that depends greatly on the physical configuration of the engine. The vibration and long-term wear posed by unbalanced firing angles can be quite detrimental to engine life.Pythagorean said:Cy, turbo,
I was also asking about the gasoline and standard aspect.
For instance, would you use the same chart for a diesel or rotary engine? It says in the subscript that it's for a V-8 engine. Is it much different for a V-6 or a straight six?
my intuition tells me it should be different for a diesel engine, but I really have no idea.
turbo-1 said:It can be very different, Pythagorean. The firing angle can affect the efficiency tremendously, and that depends greatly on the physical configuration of the engine. The vibration and long-term wear posed by unbalanced firing angles can be quite detrimental to engine life.
Ranger Mike addressed some of these variations here:
https://www.physicsforums.com/showthread.php?t=292286
He's got some practical application knowledge under his belt, and is a pretty reliable source. I have tweaked bikes much more than autos, and I gladly accept his advice on the latter. The principles are the same - the applications differ little in practice, though sometimes it's nice to have a lower-mass vehicle to tweak.Pythagorean said:wow, that's a pretty intense packet of information!
russ_watters said:Just to clarify, when you say "rolling resistance", is that where the tires meet the ground only or does it include all drive losses?
PA32R said:Yes, I'm sure I re-opened it. I stumbled on the thread by querying something or other in Google, and when I read the reply from Integral, I couldn't leave it alone. The conclusions (all else being equal, lower rpm's and relatively slow acceleration are better for fuel economy) were generally correct but his rationale for both cases was flawed.
Sorry if I've transgressed.
Rule of thumb given in driving class was about 10% drop every 10km/h.physical1 said:I have read going above 85-95km/h starts to cost more mileage due to air resistance also.
ShawnD said:Last fillup was roughly 48mpg UK (40mpg US).
ShawnD said:That's not true at all. In third gear I can go 50km/h when barely touching the gas pedal. To maintain a speed of 50km/h in fifth gear, I need to floor it. lower rpm * more fuel per ignition = similar amount of fuel being burned.
Cyrus said:I don't understand what you mean by 'loading the map you want'. The map decribes a physical system. For x RPM and x PSI you NEED y fuel flow.
Jasongreat said:...keeping the pyrometer...