what's better for gas mileage low rpm heavy pedal, high rpm light pedal?
04-22-2004, 09:55 PM
#48
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Join Date: Oct 2003
Location: Turnersville/Washington Twp. NJ
Posts: 260
haha sure, I'll think of a simple example.
2 Stock lt1 z28s at a stop light. Both are the same except one has 4 passengers while the other only has 1-driver. The load on each engine is the wieght of each car. Both cars' destinations are one mile away. Both cars accelerate with say 50% throttle and shift (both at same point) at 3000rpm. The car with the higher load is gonna take more fuel to get to the destination, this is an ineffecincey going to the engine that has the greater load.
I used alot of words to explain something simple; i may have over-simplified it, and thought about it in different terms that you were. But for basic deffinitions: engine load is wieght, and efficencey is mpg.
2 Stock lt1 z28s at a stop light. Both are the same except one has 4 passengers while the other only has 1-driver. The load on each engine is the wieght of each car. Both cars' destinations are one mile away. Both cars accelerate with say 50% throttle and shift (both at same point) at 3000rpm. The car with the higher load is gonna take more fuel to get to the destination, this is an ineffecincey going to the engine that has the greater load.
I used alot of words to explain something simple; i may have over-simplified it, and thought about it in different terms that you were. But for basic deffinitions: engine load is wieght, and efficencey is mpg.
04-22-2004, 10:05 PM
#49
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Join Date: Jul 2001
Posts: 39
Originally posted by OldSStroker
I'm surprised that the M6 gave 18% better mileage than the A4 even @ 75-80. My 96 SS (still A4
) does a little better than the 22, but not the 26 under similar circumstances. FWIW, for that mass and frontal area, the "Killer Whale" still impresses me with it's economy.
Did you ever try 6th with the original 3.08s? That should be about 1600 rpm around 80, I think. That might be too low, but I'm not sure. I'm not so sure that some Caprices didn't come with 2.56s or 1.79 final with the A4.
That you still get 25 with the cam is impressive.
No problem with "a newbie being a jackass". I don't think that at all! I hang around an SS forum, but don't see a lot to comment on. Maybe it's just the wrong forum.
Thanks for the info.
I'm surprised that the M6 gave 18% better mileage than the A4 even @ 75-80. My 96 SS (still A4
) does a little better than the 22, but not the 26 under similar circumstances. FWIW, for that mass and frontal area, the "Killer Whale" still impresses me with it's economy.Did you ever try 6th with the original 3.08s? That should be about 1600 rpm around 80, I think. That might be too low, but I'm not sure. I'm not so sure that some Caprices didn't come with 2.56s or 1.79 final with the A4.
That you still get 25 with the cam is impressive.
No problem with "a newbie being a jackass". I don't think that at all! I hang around an SS forum, but don't see a lot to comment on. Maybe it's just the wrong forum.
Thanks for the info.
I didn't use 6th much with the 3.08's...it felt like I had to keep the pedal down too far to keep the car moving, and come the slightest of hills, the car would struggle to pull up them while holding constant speed...I could go 100 mph and still be under 2000 RPM depending on what tires I rode on (taller winter snowtires or normal summer tires)....impressive to tell people, but sucked to drive with. I never did it for long enough to see what the mileage did on a specific tank though, I mostly only used it just to remind myself I had done a 6 speed conversion, not a 5 speed
. All LT1 police packages caprices came with the same 3.08's that the Impala SS got. Some civilian cars came with far worse gears like 2.56's...that would have been hillarious with the T56. As it was I could almost go 0-60 in first gear with the 3.08's, which REALLY sucked off the line.For what it's worth, I also notice a very obvious drop in mileage during winter months when they make us run "reformulated" gas. My car will lose 3-4 mpg all winter long, and then like someone flipped a switch, when we go back to regular gas, my car will come right back up to 25 mpg or so.
04-22-2004, 10:09 PM
#50
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Join Date: Jun 1999
Location: Lowcountry
Posts: 939
Ahh, but the car with more weight performed more work 
I'd put money on the fact that the car with more people, while using more fuel, did more work per fuel used.
The big difference in load is compression. A higher load creates higher compression, by virtue of more mass being introduced into the cylinder. With low load (more vacuum) there is less manifold pressure, and therefore less mass is moved into the cylinder, and therefore actual compression goes down.
To put things simply, thermal effeciency is highly affected by compression. High compression equals higher density. Higher density equals faster flame front propogation. Low compression (load) results in slower flame fronts. A fast flame front means that the fuel/air contents of the cylinder is combusted more rapidly. The faster it is "burned" the more effeciently that thermal energy is converted to kinetic energy. Think of it this way, if it takes longer to burn the fuel and air, there's more time for the heat to transfer into the engine, coolant, oil, etc. instead of producing work.
While a higher load burns more fuel, it also creates more power. This is where the idea of brake specific fuel consumption comes into play It's a matter of work done versus fuel required to do it. This is why diesels are more effecient, they are not throttled, and always see high load.
Now the only caveat to this is if you give the engine too much load it enters WOT, power enrichment. All else being equal, if you can keep the car in closed loop but at high load you will get better fuel economy.
If someone can correct any of this, I more than welcome it.... there's some smart people here
I'd put money on the fact that the car with more people, while using more fuel, did more work per fuel used.The big difference in load is compression. A higher load creates higher compression, by virtue of more mass being introduced into the cylinder. With low load (more vacuum) there is less manifold pressure, and therefore less mass is moved into the cylinder, and therefore actual compression goes down.
To put things simply, thermal effeciency is highly affected by compression. High compression equals higher density. Higher density equals faster flame front propogation. Low compression (load) results in slower flame fronts. A fast flame front means that the fuel/air contents of the cylinder is combusted more rapidly. The faster it is "burned" the more effeciently that thermal energy is converted to kinetic energy. Think of it this way, if it takes longer to burn the fuel and air, there's more time for the heat to transfer into the engine, coolant, oil, etc. instead of producing work.
While a higher load burns more fuel, it also creates more power. This is where the idea of brake specific fuel consumption comes into play
It's a matter of work done versus fuel required to do it. This is why diesels are more effecient, they are not throttled, and always see high load.Now the only caveat to this is if you give the engine too much load it enters WOT, power enrichment. All else being equal, if you can keep the car in closed loop but at high load you will get better fuel economy.
If someone can correct any of this, I more than welcome it.... there's some smart people here
04-22-2004, 10:12 PM
#51
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Join Date: Jan 2004
Location: Burbank, CA
Posts: 295
Originally posted by rpm4lalo
If I am doing 70mph and need to pass the person in front of me, I drop the T56 into 3rd and go to WOT. I bang thru the rest of gears until they are a dot in my rear view.
If I am doing 70mph and need to pass the person in front of me, I drop the T56 into 3rd and go to WOT. I bang thru the rest of gears until they are a dot in my rear view.
04-22-2004, 10:16 PM
#52
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Join Date: Jan 2004
Location: Burbank, CA
Posts: 295
Originally posted by Tony Danza
haha sure, I'll think of a simple example.
2 Stock lt1 z28s at a stop light. Both are the same except one has 4 passengers while the other only has 1-driver. The load on each engine is the wieght of each car. Both cars' destinations are one mile away. Both cars accelerate with say 50% throttle and shift (both at same point) at 3000rpm. The car with the higher load is gonna take more fuel to get to the destination, this is an ineffecincey going to the engine that has the greater load.
I used alot of words to explain something simple; i may have over-simplified it, and thought about it in different terms that you were. But for basic deffinitions: engine load is wieght, and efficencey is mpg.
haha sure, I'll think of a simple example.
2 Stock lt1 z28s at a stop light. Both are the same except one has 4 passengers while the other only has 1-driver. The load on each engine is the wieght of each car. Both cars' destinations are one mile away. Both cars accelerate with say 50% throttle and shift (both at same point) at 3000rpm. The car with the higher load is gonna take more fuel to get to the destination, this is an ineffecincey going to the engine that has the greater load.
I used alot of words to explain something simple; i may have over-simplified it, and thought about it in different terms that you were. But for basic deffinitions: engine load is wieght, and efficencey is mpg.
04-22-2004, 10:18 PM
#53
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Join Date: Jan 2004
Location: Burbank, CA
Posts: 295
Originally posted by Buttercup
Ahh, but the car with more weight performed more work I'd put money on the fact that the car with more people, while using more fuel, did more work per fuel used.
The big difference in load is compression. A higher load creates higher compression, by virtue of more mass being introduced into the cylinder. With low load (more vacuum) there is less manifold pressure, and therefore less mass is moved into the cylinder, and therefore actual compression goes down.
To put things simply, thermal effeciency is highly affected by compression. High compression equals higher density. Higher density equals faster flame front propogation. Low compression (load) results in slower flame fronts. A fast flame front means that the fuel/air contents of the cylinder is combusted more rapidly. The faster it is "burned" the more effeciently that thermal energy is converted to kinetic energy. Think of it this way, if it takes longer to burn the fuel and air, there's more time for the heat to transfer into the engine, coolant, oil, etc. instead of producing work.
While a higher load burns more fuel, it also creates more power. This is where the idea of brake specific fuel consumption comes into play It's a matter of work done versus fuel required to do it. This is why diesels are more effecient, they are not throttled, and always see high load.
Now the only caveat to this is if you give the engine too much load it enters WOT, power enrichment. All else being equal, if you can keep the car in closed loop but at high load you will get better fuel economy.
If someone can correct any of this, I more than welcome it.... there's some smart people here
Ahh, but the car with more weight performed more work
I'd put money on the fact that the car with more people, while using more fuel, did more work per fuel used.The big difference in load is compression. A higher load creates higher compression, by virtue of more mass being introduced into the cylinder. With low load (more vacuum) there is less manifold pressure, and therefore less mass is moved into the cylinder, and therefore actual compression goes down.
To put things simply, thermal effeciency is highly affected by compression. High compression equals higher density. Higher density equals faster flame front propogation. Low compression (load) results in slower flame fronts. A fast flame front means that the fuel/air contents of the cylinder is combusted more rapidly. The faster it is "burned" the more effeciently that thermal energy is converted to kinetic energy. Think of it this way, if it takes longer to burn the fuel and air, there's more time for the heat to transfer into the engine, coolant, oil, etc. instead of producing work.
While a higher load burns more fuel, it also creates more power. This is where the idea of brake specific fuel consumption comes into play
It's a matter of work done versus fuel required to do it. This is why diesels are more effecient, they are not throttled, and always see high load.Now the only caveat to this is if you give the engine too much load it enters WOT, power enrichment. All else being equal, if you can keep the car in closed loop but at high load you will get better fuel economy.
If someone can correct any of this, I more than welcome it.... there's some smart people here
ehh errmmmm, what he said!
04-22-2004, 10:23 PM
#54
Registered User
Join Date: Jun 1999
Location: Lowcountry
Posts: 939
Originally posted by z28poweredlt1
hammer = on head of nail
ehh errmmmm, what he said!
hammer = on head of nail
ehh errmmmm, what he said!
Damn I miss being here in the tech section, it's so productive
I should be studying
04-22-2004, 11:18 PM
#55
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Join Date: Dec 1969
Location: Little Rock, AR
Posts: 27,714
You're kinda losing me with talk of changes in "compression"... if you are comparing to high compression diesel engines, aren't you speaking of static compression? How does engine load change the static compression ratio?
I am not trying to compare the engine to any other, just referring to the one that is in each individual's car and how to drive it.
I do think we agree (and I sorta said this earlier) that if you keep the vacuum as high as it can be at all times, you will get the best mileage (like watching the MAP or driving with a vacuum gauge-virtually the same thing).
I am not trying to compare the engine to any other, just referring to the one that is in each individual's car and how to drive it.
I do think we agree (and I sorta said this earlier) that if you keep the vacuum as high as it can be at all times, you will get the best mileage (like watching the MAP or driving with a vacuum gauge-virtually the same thing).
04-22-2004, 11:25 PM
#56
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Join Date: Oct 2003
Location: Turnersville/Washington Twp. NJ
Posts: 260
Originally posted by Buttercup
Ahh, but the car with more weight performed more work I'd put money on the fact that the car with more people, while using more fuel, did more work per fuel used.
The big difference in load is compression. A higher load creates higher compression, by virtue of more mass being introduced into the cylinder. With low load (more vacuum) there is less manifold pressure, and therefore less mass is moved into the cylinder, and therefore actual compression goes down.
To put things simply, thermal effeciency is highly affected by compression. High compression equals higher density. Higher density equals faster flame front propogation. Low compression (load) results in slower flame fronts. A fast flame front means that the fuel/air contents of the cylinder is combusted more rapidly. The faster it is "burned" the more effeciently that thermal energy is converted to kinetic energy. Think of it this way, if it takes longer to burn the fuel and air, there's more time for the heat to transfer into the engine, coolant, oil, etc. instead of producing work.
While a higher load burns more fuel, it also creates more power. This is where the idea of brake specific fuel consumption comes into play It's a matter of work done versus fuel required to do it. This is why diesels are more effecient, they are not throttled, and always see high load.
Now the only caveat to this is if you give the engine too much load it enters WOT, power enrichment. All else being equal, if you can keep the car in closed loop but at high load you will get better fuel economy.
If someone can correct any of this, I more than welcome it.... there's some smart people here
Ahh, but the car with more weight performed more work
I'd put money on the fact that the car with more people, while using more fuel, did more work per fuel used.The big difference in load is compression. A higher load creates higher compression, by virtue of more mass being introduced into the cylinder. With low load (more vacuum) there is less manifold pressure, and therefore less mass is moved into the cylinder, and therefore actual compression goes down.
To put things simply, thermal effeciency is highly affected by compression. High compression equals higher density. Higher density equals faster flame front propogation. Low compression (load) results in slower flame fronts. A fast flame front means that the fuel/air contents of the cylinder is combusted more rapidly. The faster it is "burned" the more effeciently that thermal energy is converted to kinetic energy. Think of it this way, if it takes longer to burn the fuel and air, there's more time for the heat to transfer into the engine, coolant, oil, etc. instead of producing work.
While a higher load burns more fuel, it also creates more power. This is where the idea of brake specific fuel consumption comes into play
It's a matter of work done versus fuel required to do it. This is why diesels are more effecient, they are not throttled, and always see high load.Now the only caveat to this is if you give the engine too much load it enters WOT, power enrichment. All else being equal, if you can keep the car in closed loop but at high load you will get better fuel economy.
If someone can correct any of this, I more than welcome it.... there's some smart people here
04-22-2004, 11:27 PM
#57
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Thread Starter
Join Date: Sep 2002
Location: Arlington, VA
Posts: 2,481
Originally posted by Tony Danza
haha ok thanks for the explanation about where you were coming from. As i mentioned i might have, I oversimplified what was going on as mpg (first reaction cuz of the title of the thread), not as the engine's specificly.
haha ok thanks for the explanation about where you were coming from. As i mentioned i might have, I oversimplified what was going on as mpg (first reaction cuz of the title of the thread), not as the engine's specificly.
04-22-2004, 11:30 PM
#58
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Join Date: Oct 2003
Location: Turnersville/Washington Twp. NJ
Posts: 260
Originally posted by scoobysnax83
Hey, Hey, Hey, you can only get so specific in a thread title....
Hey, Hey, Hey, you can only get so specific in a thread title....
Dont think for a second i was whessileing (sp? im tired...) out of that and blameing you for making the "misleading" title!
04-22-2004, 11:47 PM
#60
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Join Date: Jun 1999
Location: Lowcountry
Posts: 939
Originally posted by shoebox
You're kinda losing me with talk of changes in "compression"... if you are comparing to high compression diesel engines, aren't you speaking of static compression? How does engine load change the static compression ratio?
I am not trying to compare the engine to any other, just referring to the one that is in each individual's car and how to drive it.
I do think we agree (and I sorta said this earlier) that if you keep the vacuum as high as it can be at all times, you will get the best mileage (like watching the MAP or driving with a vacuum gauge-virtually the same thing).
You're kinda losing me with talk of changes in "compression"... if you are comparing to high compression diesel engines, aren't you speaking of static compression? How does engine load change the static compression ratio?
I am not trying to compare the engine to any other, just referring to the one that is in each individual's car and how to drive it.
I do think we agree (and I sorta said this earlier) that if you keep the vacuum as high as it can be at all times, you will get the best mileage (like watching the MAP or driving with a vacuum gauge-virtually the same thing).
I'm saying completely the opposite of you
Lower vacuum = higher load = higher thermal effeciency. Provided you can stay in closed loop.The diesel comparison is just a real life example of high load effeciency. A diesel engine does not have a throttle and doesn't pull any appreciable vacuum. It's essentially run at WOT all the time and power output is controlled by the amount of fuel added. The same principle applies to the otto-cycle, though they obviously operate differently, both are hindered by the same internal combustion limitations. The addition of friction into the equation further favors, low RPM/high load.
High static compression, or more importantly dynamic compression, (and resulting running compression) improves power output does it not? High static compression makes even more difference at part throttle because it's not a linear relation. You can increase the actual running compression with your right foot
The cylinder is a fixed volume, the amount of air/fuel entering it is variable... the more air and fuel mass you can cram in there, the more it is compressed, the faster it burns, and the more effeciently that heat is converted to power (as opposed to being soaked up and blown out the radiator).Now if you're tuning, you want to achieve maximum vacuum for given conditions. This is a matter of improving VE however and is different than finding the optimum driving style for economy
We can make it even more complicated by looking at other important factors such as cam timing but I'm already getting a headache
Sorry I can't describe this better