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My car is right at 3000rpm at 70mph. Weird thing is,I get the best highway mileage when I set the cruise around 80mph.
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Which car has lowest rpms at 75mph.
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neat!
Tell us how you got an exemption from physics?
Tell us how you got an exemption from physics?
Originally Posted By: DieselTech
A smart man once told me " Revs are Free " the higher the revs the less force it takes to push the car. Therefore one is lighter on the pedal. The ONLY variable in milage is conditions and your right foot.
The last thing you want is a vehicle to struggle to maintain speed or get to speed because of poor gearing. 4 cylinder engines are meant to rev, let them do it.
I hate to say it, but that man is wrong. Revs are never free. Higher revs = more pumping loss, more friction loss, and more stress on the reciprocating parts.
Not only that, but power output required to move a car at 70mph is the same, regardless of how fast the engine is turning.
Needing less throttle at a higher RPM is NOT an indication of lower fuel consumption. Needing less throttle at the same RPM is.
I have swapped my 3.73 LSD for a 4.27 torsen, and now get 21 mpg on my commute rather than 22.6 mpg. I'm slightly miffed at the mileage, but more miffed at the 400rpm faster the engine turns at 70mph.
Long term plan is to swap the G260 for a T56 with a .5 6th gear, and a built engine (40% more umph), which will give me a cruising engine speed of 2100rpm in 6th at 70mph. I currently run at 3400rpm @ 70, the previous gearing put me at 3000rpm @ 70.
A smart man once told me " Revs are Free " the higher the revs the less force it takes to push the car. Therefore one is lighter on the pedal. The ONLY variable in milage is conditions and your right foot.
The last thing you want is a vehicle to struggle to maintain speed or get to speed because of poor gearing. 4 cylinder engines are meant to rev, let them do it.
I hate to say it, but that man is wrong. Revs are never free. Higher revs = more pumping loss, more friction loss, and more stress on the reciprocating parts.
Not only that, but power output required to move a car at 70mph is the same, regardless of how fast the engine is turning.
Needing less throttle at a higher RPM is NOT an indication of lower fuel consumption. Needing less throttle at the same RPM is.
I have swapped my 3.73 LSD for a 4.27 torsen, and now get 21 mpg on my commute rather than 22.6 mpg. I'm slightly miffed at the mileage, but more miffed at the 400rpm faster the engine turns at 70mph.
Long term plan is to swap the G260 for a T56 with a .5 6th gear, and a built engine (40% more umph), which will give me a cruising engine speed of 2100rpm in 6th at 70mph. I currently run at 3400rpm @ 70, the previous gearing put me at 3000rpm @ 70.
u3b3rg33k,
Revs are free relative for the same engine weight. The whole point is to use revs to replace displacement, and if you already want a big engine, then there is nothing that reving it higher will help.
The whole system needs to match, so that the power generated is peak and the engine size is matching this peak for the power you need, so no umph from big displacement.
Exhaust resonance need to match the power band or else you will have 80mph being more efficient than 70mph which you usually drive.
Most small displacement cars do a good job compensating for smaller engine size by tuning the power band and air flow right.
Revs are free relative for the same engine weight. The whole point is to use revs to replace displacement, and if you already want a big engine, then there is nothing that reving it higher will help.
The whole system needs to match, so that the power generated is peak and the engine size is matching this peak for the power you need, so no umph from big displacement.
Exhaust resonance need to match the power band or else you will have 80mph being more efficient than 70mph which you usually drive.
Most small displacement cars do a good job compensating for smaller engine size by tuning the power band and air flow right.
Originally Posted By: PandaBear
u3b3rg33k,
Revs are free relative for the same engine weight.
What? engine weight is not remotely relevant to cruising efficiency.
My engine (and all other stock M20B25 engines) at 6000 rpm is not more efficient than my engine at 3000 rpm. It's considerably less efficient, actually.
It's out of it's power band and it's VE is going down drastically. Therefore more revs = less efficient.
Perhaps you can re-phrase that so that it makes sense?
Everything else you say makes sense, but that other post says (arbitrarily, mind you) that more revs and less throttle is more efficient.
One cannot make that assumption.
I-4 cylinder engines are no more "meant to rev" than a one cylinder, or an H twin, H-4, or a straight 6. A specific engine may be "meant to rev" but again, such terms are not remotely scientific.
u3b3rg33k,
Revs are free relative for the same engine weight.
What? engine weight is not remotely relevant to cruising efficiency.
My engine (and all other stock M20B25 engines) at 6000 rpm is not more efficient than my engine at 3000 rpm. It's considerably less efficient, actually.
It's out of it's power band and it's VE is going down drastically. Therefore more revs = less efficient.
Perhaps you can re-phrase that so that it makes sense?
Everything else you say makes sense, but that other post says (arbitrarily, mind you) that more revs and less throttle is more efficient.
One cannot make that assumption.
I-4 cylinder engines are no more "meant to rev" than a one cylinder, or an H twin, H-4, or a straight 6. A specific engine may be "meant to rev" but again, such terms are not remotely scientific.
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Originally Posted By: u3b3rg33k
Originally Posted By: PandaBear
u3b3rg33k,
Revs are free relative for the same engine weight.
What? engine weight is not remotely relevant to cruising efficiency.
My engine (and all other stock M20B25 engines) at 6000 rpm is not more efficient than my engine at 3000 rpm. It's considerably less efficient, actually.
It's out of it's power band and it's VE is going down drastically. Therefore more revs = less efficient.
Perhaps you can re-phrase that so that it makes sense?
Everything else you say makes sense, but that other post says (arbitrarily, mind you) that more revs and less throttle is more efficient.
One cannot make that assumption.
I-4 cylinder engines are no more "meant to rev" than a one cylinder, or an H twin, H-4, or a straight 6. A specific engine may be "meant to rev" but again, such terms are not remotely scientific.
Indeed. Cylinder head flow and camshaft profile have MASSIVELY more impact on the engine's RPM capabilities and power band than the number of cylinders it has.
Originally Posted By: PandaBear
u3b3rg33k,
Revs are free relative for the same engine weight.
What? engine weight is not remotely relevant to cruising efficiency.
My engine (and all other stock M20B25 engines) at 6000 rpm is not more efficient than my engine at 3000 rpm. It's considerably less efficient, actually.
It's out of it's power band and it's VE is going down drastically. Therefore more revs = less efficient.
Perhaps you can re-phrase that so that it makes sense?
Everything else you say makes sense, but that other post says (arbitrarily, mind you) that more revs and less throttle is more efficient.
One cannot make that assumption.
I-4 cylinder engines are no more "meant to rev" than a one cylinder, or an H twin, H-4, or a straight 6. A specific engine may be "meant to rev" but again, such terms are not remotely scientific.
Indeed. Cylinder head flow and camshaft profile have MASSIVELY more impact on the engine's RPM capabilities and power band than the number of cylinders it has.
Originally Posted By: u3b3rg33k
Everything else you say makes sense, but that other post says (arbitrarily, mind you) that more revs and less throttle is more efficient.
Maybe I really should rephrase what I was trying to say, sorry.
What I meant was: if you only need a small amount of power, why would you want to rev it higher than you can minimally get away (realistically, not lugging it of course). When you already have a specific size engine displacement, you will want to use the minimum amount of rev to reduce plumbing loss. But, when you have a choice of using a smaller engine at higher rpm vs the larger engine at smaller rpm for the same amount of power output, then smaller engine at higher rpm will usually (usually is the word here) be more efficient because of reduced weight, friction, and engine metal material cost (assume same complexity).
Therefore rev is free when you want to give more power output for the same amount of material.
Everything else you say makes sense, but that other post says (arbitrarily, mind you) that more revs and less throttle is more efficient.
Maybe I really should rephrase what I was trying to say, sorry.
What I meant was: if you only need a small amount of power, why would you want to rev it higher than you can minimally get away (realistically, not lugging it of course). When you already have a specific size engine displacement, you will want to use the minimum amount of rev to reduce plumbing loss. But, when you have a choice of using a smaller engine at higher rpm vs the larger engine at smaller rpm for the same amount of power output, then smaller engine at higher rpm will usually (usually is the word here) be more efficient because of reduced weight, friction, and engine metal material cost (assume same complexity).
Therefore rev is free when you want to give more power output for the same amount of material.
I had a 1990 Chevrolet Caprice, 5.0 V8 engine and automatic, that turned 1350 RPM at 60 MPH based on calculation of tire sizes, rear axle ratio, and transmission ratio in top gear. It was a marvelous long distance cruiser and economical in that use. Currently, I believe that the slowest highway engine RPM is found on the new Lexus LS 460h L hybrid with the 5.0 engine.
1750 @ 65 mph 29 mpg
If you have the torque profile of the engine then find out where the engine produces the highest torque per RPM. That is more likely the best RPM that uses leat gas. In some engines it is actually where the Torque/rpm meets the power/rpm curve.
Having said that weight and coefficient of drag are two major factors in MPG as well. Short and light weight cars are good mpg'ers.
Most vehichles now are tuned to deliever the best MPG between 55~65 mph but not all.
Having said that weight and coefficient of drag are two major factors in MPG as well. Short and light weight cars are good mpg'ers.
Most vehichles now are tuned to deliever the best MPG between 55~65 mph but not all.
2000 @ 75mph, 2150 @ 80mph (see sig for car)
I think in many cars currently on the road, ultimate highway economy is sacrificed for comfort and driveability, especially if we're talking a 4spd auto (like mine). More gears and faster shifting allows the auto engineers to create a car that will seamlessly switch from "econo-cruise" to "pass-that-slow-poking-#$^%-right-NOW" mode and not give up anything in the rest of the gearbox.
I think in many cars currently on the road, ultimate highway economy is sacrificed for comfort and driveability, especially if we're talking a 4spd auto (like mine). More gears and faster shifting allows the auto engineers to create a car that will seamlessly switch from "econo-cruise" to "pass-that-slow-poking-#$^%-right-NOW" mode and not give up anything in the rest of the gearbox.
Originally Posted By: 440Magnum
That's not true for all vehicles. Take Jeep Cherokees for example. The automatic versions have a 0.75 overdrive in the transmission and are normally equipped with 3.55 ratio axles, for a final drive ratio of 2.66:1
On the other hand, the 5-speed stick versions have a 0.79 overdrive and are equipped with a 3.23 axle unless optioned otherwise, for a final drive ratio of 2.55:1. Very close to the same, but the automatic actually turns a few more RPM at cruise than the stick.
Old post, but:
The manuals with 4.0 have 3.07s in the rear, 2.5l Manuals have 4.11s.
The ax-15 manual has a .85 fifth gear, so does the ax-5. (4.0 and 2.5 manual transmissions)
Auto 4.0 has 3.55s, or 3.73s with the towing package.
.75 overdrive in the AW4 (only auto trans used with 4.0)
The TF-99 used with the 2.5l in 91 has a 1:1 final gear.
The 30RH/32RH used '94-'00 with 2.5l had a 1:1 final gear also.
Anyway, My girlfriends Stock 96 Cherokee. 4.0l Auto, no lift and 235/75s is at ~2100 at an indicated 70MPH.
Dont know what my 89 runs at, I dont have a tach
That's not true for all vehicles. Take Jeep Cherokees for example. The automatic versions have a 0.75 overdrive in the transmission and are normally equipped with 3.55 ratio axles, for a final drive ratio of 2.66:1
On the other hand, the 5-speed stick versions have a 0.79 overdrive and are equipped with a 3.23 axle unless optioned otherwise, for a final drive ratio of 2.55:1. Very close to the same, but the automatic actually turns a few more RPM at cruise than the stick.
Old post, but:
The manuals with 4.0 have 3.07s in the rear, 2.5l Manuals have 4.11s.
The ax-15 manual has a .85 fifth gear, so does the ax-5. (4.0 and 2.5 manual transmissions)
Auto 4.0 has 3.55s, or 3.73s with the towing package.
.75 overdrive in the AW4 (only auto trans used with 4.0)
The TF-99 used with the 2.5l in 91 has a 1:1 final gear.
The 30RH/32RH used '94-'00 with 2.5l had a 1:1 final gear also.
Anyway, My girlfriends Stock 96 Cherokee. 4.0l Auto, no lift and 235/75s is at ~2100 at an indicated 70MPH.
Dont know what my 89 runs at, I dont have a tach
Ahhhh...... Anyone remember back in the 80's when when many four bangers would luff along at barely 2200 RPM's @ 70MPH? There were a few exceptions though. As opposed to the 70's when four bangers were much higher revving. Anyone remember the mileage those cars got.
A low revving 4cyl sounds like it's lugging compared to a V8 since it has 1/2 the combustion cycles per revolution.
A low revving 4cyl sounds like it's lugging compared to a V8 since it has 1/2 the combustion cycles per revolution.
My 1998 Corvette Manual 6 speed runs 1250 rpms @ 65 mph. I have gotten 33.6 mpg on a level road trip, pretty good for 345 HP !
The runflat tires get 3 mpg better mileage than regular radials due to their stiffer sidewalls and less rolling resistance.
The runflat tires get 3 mpg better mileage than regular radials due to their stiffer sidewalls and less rolling resistance.
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Originally Posted By: expat
Quote:My 1998 Corvette Manual 6 speed runs 1250 rpms @ 65 mph. I have gotten 33.6 mpg on a level road trip, pretty good for 345 HP
345hp @ 1250rpm 'REALLY' is good.
33.6 mpg @ 65mpg for a car with such a lo CD is not really good at all!
REALLY, what does YOUR car get at 65 mph and what is it's total HP? What mileage do YOU think I should be getting, EPA is 18/28 mpg ?
Quote:My 1998 Corvette Manual 6 speed runs 1250 rpms @ 65 mph. I have gotten 33.6 mpg on a level road trip, pretty good for 345 HP
345hp @ 1250rpm 'REALLY' is good.
33.6 mpg @ 65mpg for a car with such a lo CD is not really good at all!
REALLY, what does YOUR car get at 65 mph and what is it's total HP? What mileage do YOU think I should be getting, EPA is 18/28 mpg ?
Quote;REALLY, what does YOUR car get at 65 mph and what is it's total HP?
You miss the point. This is not a urinating contest!
The point is, your car may be capable of producing 345hp, but at 65mph you would only be using (at a guess) 10% of that power.
So if the car only gets 33.6 mph at 65 mph (considering that the car is a light, Aerodynamic, two seater) the engine is not producing that 35 (or whatever) hp particularly efficiently.
You just got a Big engine working against you when it comes to Low/moderate speed economy.
For what it's worth, all three of my Vehicles would get better, steady state economy at 65.
On a daily driver (or road car) I would have no need of anything like 345 hp!
You miss the point. This is not a urinating contest!
The point is, your car may be capable of producing 345hp, but at 65mph you would only be using (at a guess) 10% of that power.
So if the car only gets 33.6 mph at 65 mph (considering that the car is a light, Aerodynamic, two seater) the engine is not producing that 35 (or whatever) hp particularly efficiently.
You just got a Big engine working against you when it comes to Low/moderate speed economy.
For what it's worth, all three of my Vehicles would get better, steady state economy at 65.
On a daily driver (or road car) I would have no need of anything like 345 hp!
Originally Posted By: expat
Quote;REALLY, what does YOUR car get at 65 mph and what is it's total HP?
You miss the point. This is not a urinating contest!
The point is, your car may be capable of producing 345hp, but at 65mph you would only be using (at a guess) 10% of that power.
So if the car only gets 33.6 mph at 65 mph (considering that the car is a light, Aerodynamic, two seater) the engine is not producing that 35 (or whatever) hp particularly efficiently.
You just got a Big engine working against you when it comes to Low/moderate speed economy.
For what it's worth, all three of my Vehicles would get better, steady state economy at 65.
On a daily driver (or road car) I would have no need of anything like 345 hp!
He did say the mileage was for a road trip, not instantaneous mileage which is probably high 30's to average 33.6 mpg. All in all the corvette gets impressive mileage compared to its competitors with similar performance though. That is not easy to do, engine design wise, and chevrolet did a pretty good job at it.
You seem to happy with a transportation appliance, most corvette buyers want a bit more of an experience and if it happens to get Camry mileage then its a bonus.
Quote;REALLY, what does YOUR car get at 65 mph and what is it's total HP?
You miss the point. This is not a urinating contest!
The point is, your car may be capable of producing 345hp, but at 65mph you would only be using (at a guess) 10% of that power.
So if the car only gets 33.6 mph at 65 mph (considering that the car is a light, Aerodynamic, two seater) the engine is not producing that 35 (or whatever) hp particularly efficiently.
You just got a Big engine working against you when it comes to Low/moderate speed economy.
For what it's worth, all three of my Vehicles would get better, steady state economy at 65.
On a daily driver (or road car) I would have no need of anything like 345 hp!
He did say the mileage was for a road trip, not instantaneous mileage which is probably high 30's to average 33.6 mpg. All in all the corvette gets impressive mileage compared to its competitors with similar performance though. That is not easy to do, engine design wise, and chevrolet did a pretty good job at it.
You seem to happy with a transportation appliance, most corvette buyers want a bit more of an experience and if it happens to get Camry mileage then its a bonus.
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Originally Posted By: IndyIan
Originally Posted By: expat
Quote;REALLY, what does YOUR car get at 65 mph and what is it's total HP?
You miss the point. This is not a urinating contest!
The point is, your car may be capable of producing 345hp, but at 65mph you would only be using (at a guess) 10% of that power.
So if the car only gets 33.6 mph at 65 mph (considering that the car is a light, Aerodynamic, two seater) the engine is not producing that 35 (or whatever) hp particularly efficiently.
You just got a Big engine working against you when it comes to Low/moderate speed economy.
For what it's worth, all three of my Vehicles would get better, steady state economy at 65.
On a daily driver (or road car) I would have no need of anything like 345 hp!
He did say the mileage was for a road trip, not instantaneous mileage which is probably high 30's to average 33.6 mpg. All in all the corvette gets impressive mileage compared to its competitors with similar performance though. That is not easy to do, engine design wise, and chevrolet did a pretty good job at it.
You seem to happy with a transportation appliance, most corvette buyers want a bit more of an experience and if it happens to get Camry mileage then its a bonus.
Well put, I guess it was HE who missed the point ! And yes I do get about 43 mpg INSTANT mileage at 65 mph. The 33.6 mpg was for a 160 mile road trip in Maryland which included stop lights and city driving. Driving to work and around town, I get 22.5 mpg, the same as my 205 HP 6 cylinder Impala.
Chevy did a GREAT job on the Corvette. As far as I know, it is the ONLY 8 cylinder high performance car that does NOT have to pay a gas guzzler tax. Handling is even more impressive than it's straight line performance. And it is my daily driver with 126,000 miles (on a 1998), what fun.
Originally Posted By: expat
Quote;REALLY, what does YOUR car get at 65 mph and what is it's total HP?
You miss the point. This is not a urinating contest!
The point is, your car may be capable of producing 345hp, but at 65mph you would only be using (at a guess) 10% of that power.
So if the car only gets 33.6 mph at 65 mph (considering that the car is a light, Aerodynamic, two seater) the engine is not producing that 35 (or whatever) hp particularly efficiently.
You just got a Big engine working against you when it comes to Low/moderate speed economy.
For what it's worth, all three of my Vehicles would get better, steady state economy at 65.
On a daily driver (or road car) I would have no need of anything like 345 hp!
He did say the mileage was for a road trip, not instantaneous mileage which is probably high 30's to average 33.6 mpg. All in all the corvette gets impressive mileage compared to its competitors with similar performance though. That is not easy to do, engine design wise, and chevrolet did a pretty good job at it.
You seem to happy with a transportation appliance, most corvette buyers want a bit more of an experience and if it happens to get Camry mileage then its a bonus.
Well put, I guess it was HE who missed the point ! And yes I do get about 43 mpg INSTANT mileage at 65 mph. The 33.6 mpg was for a 160 mile road trip in Maryland which included stop lights and city driving. Driving to work and around town, I get 22.5 mpg, the same as my 205 HP 6 cylinder Impala.
Chevy did a GREAT job on the Corvette. As far as I know, it is the ONLY 8 cylinder high performance car that does NOT have to pay a gas guzzler tax. Handling is even more impressive than it's straight line performance. And it is my daily driver with 126,000 miles (on a 1998), what fun.
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