The sixth gear ratio in my T56 is 0.57.....great for the highway, but odd to have to downshift to pass in a big V8....lol
Which car has lowest rpms at 75mph.
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My Tbird does exactly
2000 rpm @ 70
2500 @ 85
2000 rpm @ 70
2500 @ 85
Originally Posted By: LS2JSTS
The sixth gear ratio in my T56 is 0.57.....great for the highway, but odd to have to downshift to pass in a big V8....lol
You bring up an excellent point and one that explains why 4 cylinder cars, especially 4 cylinder manual transmission cars, run such high revs. In an auto, the trans can control the downshift. If you come up to a grade, it will hit a downshift and continue climbing with abput the same throttle opening. It may lose some speed, but it will continue climbing fairly well. With a manual trans, if you put the engine cruising speed too far below the torque peak, it will immedialy begin losing significant amount of speed on that grade unless you feed it significantly more throttle or manually downshift.
A friend has a 1.8T VW Jetta in which he replaced the 5th gear with one from a Jetta TDI. I believe there were three different 5th gear ratios used in the TDI, he chose the tallest (lowest numerically) thinking it would return the best fuel economy. It ended up being a wash in terms of fuel economy. He has to lay into the throttle much more when passing or climbing grades. Outside of the fuel economy wash, he says it's not much fun to drive on the expressway and requires constant working of the throttle. Cruise control also loses lots of speed when climbing hills before it accelerates to catch up. Last I knew, he was going to switch out to the lowest (highest numerically) TDI 5th gear ratio, which is still lower than the factory 1.8T gearing.
The sixth gear ratio in my T56 is 0.57.....great for the highway, but odd to have to downshift to pass in a big V8....lol
You bring up an excellent point and one that explains why 4 cylinder cars, especially 4 cylinder manual transmission cars, run such high revs. In an auto, the trans can control the downshift. If you come up to a grade, it will hit a downshift and continue climbing with abput the same throttle opening. It may lose some speed, but it will continue climbing fairly well. With a manual trans, if you put the engine cruising speed too far below the torque peak, it will immedialy begin losing significant amount of speed on that grade unless you feed it significantly more throttle or manually downshift.
A friend has a 1.8T VW Jetta in which he replaced the 5th gear with one from a Jetta TDI. I believe there were three different 5th gear ratios used in the TDI, he chose the tallest (lowest numerically) thinking it would return the best fuel economy. It ended up being a wash in terms of fuel economy. He has to lay into the throttle much more when passing or climbing grades. Outside of the fuel economy wash, he says it's not much fun to drive on the expressway and requires constant working of the throttle. Cruise control also loses lots of speed when climbing hills before it accelerates to catch up. Last I knew, he was going to switch out to the lowest (highest numerically) TDI 5th gear ratio, which is still lower than the factory 1.8T gearing.
My 4-cyl car does 4100 rpm at 75 mph and gets a measured 36 mpg (US) driving at around 60 mph which is our highway speed limit.
30 MPG on the highway is very easy for a 6 speed Vette, I've gotten 32 on the highway with a strong tail wind
ls1mike
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I have seen 30 MPG on the Highway in my Trans Am with the 6 speed as well.
But can you get that measured on tank fill-up or is that just a trip computer readout?
ls1mike
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Tank fill up, the Trans Am has no computer read out.
Originally Posted By: Gator
...Honda's rev a little too high, which translates into lower fuel economy.
Not my Honda. It tachs in at around 2K at 75mph. 2008 Honda Odyssey, 3.5L, 5spd auto. It's a great combo for long highway runs, but I hate it for 'round town, which is mostly what this van does. Annoying as heck when the trans hunts/jumps all over the place. You can't put it in 4th either. If you disable OD it stays in 3rd which is too low.
Joel
...Honda's rev a little too high, which translates into lower fuel economy.
Not my Honda. It tachs in at around 2K at 75mph. 2008 Honda Odyssey, 3.5L, 5spd auto. It's a great combo for long highway runs, but I hate it for 'round town, which is mostly what this van does. Annoying as heck when the trans hunts/jumps all over the place. You can't put it in 4th either. If you disable OD it stays in 3rd which is too low.
Joel
My GTO is somewhere around 2000 or just under at 75 mph. Not sure what my truck is as it has no tach, but it's probably similar.
I usually get 25-26 mpg with the GTO, but it's a lot heavier than the F-body and Vette so it makes sense.
I usually get 25-26 mpg with the GTO, but it's a lot heavier than the F-body and Vette so it makes sense.
Originally Posted By: MrHorspwer
Originally Posted By: LS2JSTS
The sixth gear ratio in my T56 is 0.57.....great for the highway, but odd to have to downshift to pass in a big V8....lol
You bring up an excellent point and one that explains why 4 cylinder cars, especially 4 cylinder manual transmission cars, run such high revs. In an auto, the trans can control the downshift. If you come up to a grade, it will hit a downshift and continue climbing with abput the same throttle opening. It may lose some speed, but it will continue climbing fairly well. With a manual trans, if you put the engine cruising speed too far below the torque peak, it will immedialy begin losing significant amount of speed on that grade unless you feed it significantly more throttle or manually downshift.
A friend has a 1.8T VW Jetta in which he replaced the 5th gear with one from a Jetta TDI. I believe there were three different 5th gear ratios used in the TDI, he chose the tallest (lowest numerically) thinking it would return the best fuel economy. It ended up being a wash in terms of fuel economy. He has to lay into the throttle much more when passing or climbing grades. Outside of the fuel economy wash, he says it's not much fun to drive on the expressway and requires constant working of the throttle. Cruise control also loses lots of speed when climbing hills before it accelerates to catch up. Last I knew, he was going to switch out to the lowest (highest numerically) TDI 5th gear ratio, which is still lower than the factory 1.8T gearing.
Does your buddy have a scanguage? To see what's going on it real time? I would've thought even a gas ,small turbo, engine could build enough boost to pull a taller top gear. Maybe its ECU is not a fan of boost at low rpms? The turbo makes things complicated at low rpms and bigger throttle openings.
It would be interesting to see a brake specific fuel consumption chart for that engine.
Here is a list of some BFSC charts on ecomodder.com http://ecomodder.com/forum/showthread.php/bsfc-chart-thread-post-em-if-you-got-1466.html
It shows that auto engineers have to think about many many variables when they decide on a top gear ratio for a car.
Optimizing mileage is one of them but people don't like to use a lot of throttle at low rpms on the highway, that's why alot of manual trans cars have higher top gear ratios than the auto trans version, which is unfortunate as alot of engines turn gas into energy best at 1500 to 2500 rpm and half to 3/4 throttle...
This is where drive by wire and a CVT should be able to work some mileage magic but I haven't seen this so far. It should be able to adjust the rpms and thottle to put the engine in the most efficient part of its bfsc chart based on the required power output.
Originally Posted By: LS2JSTS
The sixth gear ratio in my T56 is 0.57.....great for the highway, but odd to have to downshift to pass in a big V8....lol
You bring up an excellent point and one that explains why 4 cylinder cars, especially 4 cylinder manual transmission cars, run such high revs. In an auto, the trans can control the downshift. If you come up to a grade, it will hit a downshift and continue climbing with abput the same throttle opening. It may lose some speed, but it will continue climbing fairly well. With a manual trans, if you put the engine cruising speed too far below the torque peak, it will immedialy begin losing significant amount of speed on that grade unless you feed it significantly more throttle or manually downshift.
A friend has a 1.8T VW Jetta in which he replaced the 5th gear with one from a Jetta TDI. I believe there were three different 5th gear ratios used in the TDI, he chose the tallest (lowest numerically) thinking it would return the best fuel economy. It ended up being a wash in terms of fuel economy. He has to lay into the throttle much more when passing or climbing grades. Outside of the fuel economy wash, he says it's not much fun to drive on the expressway and requires constant working of the throttle. Cruise control also loses lots of speed when climbing hills before it accelerates to catch up. Last I knew, he was going to switch out to the lowest (highest numerically) TDI 5th gear ratio, which is still lower than the factory 1.8T gearing.
Does your buddy have a scanguage? To see what's going on it real time? I would've thought even a gas ,small turbo, engine could build enough boost to pull a taller top gear. Maybe its ECU is not a fan of boost at low rpms? The turbo makes things complicated at low rpms and bigger throttle openings.
It would be interesting to see a brake specific fuel consumption chart for that engine.
Here is a list of some BFSC charts on ecomodder.com http://ecomodder.com/forum/showthread.php/bsfc-chart-thread-post-em-if-you-got-1466.html
It shows that auto engineers have to think about many many variables when they decide on a top gear ratio for a car.
Optimizing mileage is one of them but people don't like to use a lot of throttle at low rpms on the highway, that's why alot of manual trans cars have higher top gear ratios than the auto trans version, which is unfortunate as alot of engines turn gas into energy best at 1500 to 2500 rpm and half to 3/4 throttle...
This is where drive by wire and a CVT should be able to work some mileage magic but I haven't seen this so far. It should be able to adjust the rpms and thottle to put the engine in the most efficient part of its bfsc chart based on the required power output.
Originally Posted By: IndyIan
This is where drive by wire and a CVT should be able to work some mileage magic but I haven't seen this so far. It should be able to adjust the rpms and thottle to put the engine in the most efficient part of its bfsc chart based on the required power output.
Umm, Toyota Prius does this.
This is where drive by wire and a CVT should be able to work some mileage magic but I haven't seen this so far. It should be able to adjust the rpms and thottle to put the engine in the most efficient part of its bfsc chart based on the required power output.
Umm, Toyota Prius does this.
Quote:
Does your buddy have a scanguage? To see what's going on it real time? I would've thought even a gas ,small turbo, engine could build enough boost to pull a taller top gear. Maybe its ECU is not a fan of boost at low rpms? The turbo makes things complicated at low rpms and bigger throttle openings.
As far as I know, he doesn't even have a boost gauge. He's a funny guy like that. Goes through all the trouble of swapping out the top gear, which I guess wasn't a big deal since he already had the trans out to do a clutch, but doesn't have something as simple as a boost gauge.
I do agree with your theory though. Many modern cars don't make much part-throttle boost. I know in my experience with Subaru, this is the case. I wouldn't doubt it to be the same in the VW.
In his words, "5th gear at 70 is like trying to drive 35 MPH in 5th with the old gearset."
I used him as an example to highlight that RPM doesn't always equal MPG and there are alot of factors that go in to choosing gearing. FWIW, my 1.6L Miata would regularly return 30-35 MPG doing 70-75 MPH spinning at 4,000+ RPM.
Does your buddy have a scanguage? To see what's going on it real time? I would've thought even a gas ,small turbo, engine could build enough boost to pull a taller top gear. Maybe its ECU is not a fan of boost at low rpms? The turbo makes things complicated at low rpms and bigger throttle openings.
As far as I know, he doesn't even have a boost gauge. He's a funny guy like that. Goes through all the trouble of swapping out the top gear, which I guess wasn't a big deal since he already had the trans out to do a clutch, but doesn't have something as simple as a boost gauge.
I do agree with your theory though. Many modern cars don't make much part-throttle boost. I know in my experience with Subaru, this is the case. I wouldn't doubt it to be the same in the VW.
In his words, "5th gear at 70 is like trying to drive 35 MPH in 5th with the old gearset."
I used him as an example to highlight that RPM doesn't always equal MPG and there are alot of factors that go in to choosing gearing. FWIW, my 1.6L Miata would regularly return 30-35 MPG doing 70-75 MPH spinning at 4,000+ RPM.
On my old 84 Rabbit I used to do extensive highway travel. fuel economy wasn't good, even with the 1.8 and the 5 speed stick.
The following summer I had an 86 325es with a bigger 2.7, inline 6 and a 5 speed stick.
The bmw got far better fuel economy and had much lower rpm's
The following summer I had an 86 325es with a bigger 2.7, inline 6 and a 5 speed stick.
The bmw got far better fuel economy and had much lower rpm's
Originally Posted By: Stanley Rockafeller
The following summer I had an 86 325es with a bigger 2.7, inline 6 and a 5 speed stick.
The bmw got far better fuel economy and had much lower rpm's
The 325es was specifically designed for highway fuel economy.
The following summer I had an 86 325es with a bigger 2.7, inline 6 and a 5 speed stick.
The bmw got far better fuel economy and had much lower rpm's
The 325es was specifically designed for highway fuel economy.
Originally Posted By: expat
Originally Posted By: Gator
I was wanting to no which auto has the lowest rpms at 75 mph on interstate. Honda's rev a little too high, which translates into lower fuel economy.
Not necessarily. A smaller, higher revving engine will often produce better MPG than a larger, slower revving engine.
If it was just that simple, cars would have super tall gearing.
Back when we were building hybrid cars for research in college, the data we gather from various auto companies said that 4k rpm is the peak of efficiency band for most type of design, and therefore engine sizing and gear ratio should target for this rpm for the vehicle at speed.
A 1.6L running at 4k rpm will be more efficient than a 3.2 running at 2k rpm in the same car, but noisier.
Originally Posted By: Gator
I was wanting to no which auto has the lowest rpms at 75 mph on interstate. Honda's rev a little too high, which translates into lower fuel economy.
Not necessarily. A smaller, higher revving engine will often produce better MPG than a larger, slower revving engine.
If it was just that simple, cars would have super tall gearing.
Back when we were building hybrid cars for research in college, the data we gather from various auto companies said that 4k rpm is the peak of efficiency band for most type of design, and therefore engine sizing and gear ratio should target for this rpm for the vehicle at speed.
A 1.6L running at 4k rpm will be more efficient than a 3.2 running at 2k rpm in the same car, but noisier.
Originally Posted By: IndyIan
It shows that auto engineers have to think about many many variables when they decide on a top gear ratio for a car.
Optimizing mileage is one of them but people don't like to use a lot of throttle at low rpms on the highway, that's why alot of manual trans cars have higher top gear ratios than the auto trans version, which is unfortunate as alot of engines turn gas into energy best at 1500 to 2500 rpm and half to 3/4 throttle...
This is where drive by wire and a CVT should be able to work some mileage magic but I haven't seen this so far. It should be able to adjust the rpms and thottle to put the engine in the most efficient part of its bfsc chart based on the required power output.
The main reason automatic has taller gearing than manual is because it can afford to with a torque converter, which let you amplify the amount of torque as needed when unlock. Manual doesn't have this, so it has to have a shorter gearing to get the torque relatively speaking. Also most manual car drivers like performance, so you can say it is a marketing decision rather than a strictly engineering decision.
A well tuned CVT for fuel efficiency will keep the engine running at the peak of its efficiency band (not power band), which is usually 40%-50% of the redline and depends on the valve control (VTEC, VVTi, Vano, Mitec, etc). The reason most CVT in consumer cars aren't driven this way is because people don't like a car that drive like a boat, where engine will rev but nothing happen for a few seconds, then it suddenly quiet down and go fast (aka rubber band effect by some auto journalists). People expect a car to push them back for a bit when accelerate while the engine doesn't change much in tone (ok about volume change, but not the frequency/tone), so the CVT runs like a typical transmission with more ratio, rather than the constant change in rpm and the huge variation in power output like they were ideal for.
It shows that auto engineers have to think about many many variables when they decide on a top gear ratio for a car.
Optimizing mileage is one of them but people don't like to use a lot of throttle at low rpms on the highway, that's why alot of manual trans cars have higher top gear ratios than the auto trans version, which is unfortunate as alot of engines turn gas into energy best at 1500 to 2500 rpm and half to 3/4 throttle...
This is where drive by wire and a CVT should be able to work some mileage magic but I haven't seen this so far. It should be able to adjust the rpms and thottle to put the engine in the most efficient part of its bfsc chart based on the required power output.
The main reason automatic has taller gearing than manual is because it can afford to with a torque converter, which let you amplify the amount of torque as needed when unlock. Manual doesn't have this, so it has to have a shorter gearing to get the torque relatively speaking. Also most manual car drivers like performance, so you can say it is a marketing decision rather than a strictly engineering decision.
A well tuned CVT for fuel efficiency will keep the engine running at the peak of its efficiency band (not power band), which is usually 40%-50% of the redline and depends on the valve control (VTEC, VVTi, Vano, Mitec, etc). The reason most CVT in consumer cars aren't driven this way is because people don't like a car that drive like a boat, where engine will rev but nothing happen for a few seconds, then it suddenly quiet down and go fast (aka rubber band effect by some auto journalists). People expect a car to push them back for a bit when accelerate while the engine doesn't change much in tone (ok about volume change, but not the frequency/tone), so the CVT runs like a typical transmission with more ratio, rather than the constant change in rpm and the huge variation in power output like they were ideal for.
Originally Posted By: PandaBear
A well tuned CVT for fuel efficiency will keep the engine running at the peak of its efficiency band (not power band), which is usually 40%-50% of the redline and depends on the valve control (VTEC, VVTi, Vano, Mitec, etc). The reason most CVT in consumer cars aren't driven this way is because people don't like a car that drive like a boat, where engine will rev but nothing happen for a few seconds, then it suddenly quiet down and go fast (aka rubber band effect by some auto journalists).
Around town, our Altima V6 with the CVT cruises at around 1500 rpm (IIRC), sometimes lower. But the moment you dip into the accelerator, the RPM goes up to about 2k at the minimum. Usually you won't need more than about 2k to really get this car moving anyway, which is probably why you don't get the "rubber band effect" with this powertrain.
A well tuned CVT for fuel efficiency will keep the engine running at the peak of its efficiency band (not power band), which is usually 40%-50% of the redline and depends on the valve control (VTEC, VVTi, Vano, Mitec, etc). The reason most CVT in consumer cars aren't driven this way is because people don't like a car that drive like a boat, where engine will rev but nothing happen for a few seconds, then it suddenly quiet down and go fast (aka rubber band effect by some auto journalists).
Around town, our Altima V6 with the CVT cruises at around 1500 rpm (IIRC), sometimes lower. But the moment you dip into the accelerator, the RPM goes up to about 2k at the minimum. Usually you won't need more than about 2k to really get this car moving anyway, which is probably why you don't get the "rubber band effect" with this powertrain.
Originally Posted By: PandaBear
Back when we were building hybrid cars for research in college, the data we gather from various auto companies said that 4k rpm is the peak of efficiency band for most type of design, and therefore engine sizing and gear ratio should target for this rpm for the vehicle at speed.
You misinterpreted the data.
Peak efficiency rpm depends on engine design, and more importantly on the amount of power being produced.
The old wives tale is that peak efficiency occurs at the same rpm as peak torque. That is correct within 10% or so as long as you are at full throttle.
When you are using much less than full power, then peak efficiency for that power level occurs at much less than peak torque RPM. That is why Critic's's mother's Altima CVC keeps the rpms in the 1500-2000 range. As a SWAG, torque peak on that engine is prolly close to 4000 rpm
That is also why the Corvette with a 4000 rpm torque peak runs the engine at 1500 rpm at 70 mph.
Back when we were building hybrid cars for research in college, the data we gather from various auto companies said that 4k rpm is the peak of efficiency band for most type of design, and therefore engine sizing and gear ratio should target for this rpm for the vehicle at speed.
You misinterpreted the data.
Peak efficiency rpm depends on engine design, and more importantly on the amount of power being produced.
The old wives tale is that peak efficiency occurs at the same rpm as peak torque. That is correct within 10% or so as long as you are at full throttle.
When you are using much less than full power, then peak efficiency for that power level occurs at much less than peak torque RPM. That is why Critic's's mother's Altima CVC keeps the rpms in the 1500-2000 range. As a SWAG, torque peak on that engine is prolly close to 4000 rpm
That is also why the Corvette with a 4000 rpm torque peak runs the engine at 1500 rpm at 70 mph.
Originally Posted By: XS650
Originally Posted By: PandaBear
Back when we were building hybrid cars for research in college, the data we gather from various auto companies said that 4k rpm is the peak of efficiency band for most type of design, and therefore engine sizing and gear ratio should target for this rpm for the vehicle at speed.
You misinterpreted the data.
Peak efficiency rpm depends on engine design, and more importantly on the amount of power being produced.
The old wives tale is that peak efficiency occurs at the same rpm as peak torque. That is correct within 10% or so as long as you are at full throttle.
When you are using much less than full power, then peak efficiency for that power level occurs at much less than peak torque RPM. That is why Critic's's mother's Altima CVC keeps the rpms in the 1500-2000 range. As a SWAG, torque peak on that engine is prolly close to 4000 rpm
That is also why the Corvette with a 4000 rpm torque peak runs the engine at 1500 rpm at 70 mph.
True. We had an 1L engine that is almost always running near peak throttle to replace a 3L, and a 75kw electric motor that does the acceleration for us.
Originally Posted By: PandaBear
Back when we were building hybrid cars for research in college, the data we gather from various auto companies said that 4k rpm is the peak of efficiency band for most type of design, and therefore engine sizing and gear ratio should target for this rpm for the vehicle at speed.
You misinterpreted the data.
Peak efficiency rpm depends on engine design, and more importantly on the amount of power being produced.
The old wives tale is that peak efficiency occurs at the same rpm as peak torque. That is correct within 10% or so as long as you are at full throttle.
When you are using much less than full power, then peak efficiency for that power level occurs at much less than peak torque RPM. That is why Critic's's mother's Altima CVC keeps the rpms in the 1500-2000 range. As a SWAG, torque peak on that engine is prolly close to 4000 rpm
That is also why the Corvette with a 4000 rpm torque peak runs the engine at 1500 rpm at 70 mph.
True. We had an 1L engine that is almost always running near peak throttle to replace a 3L, and a 75kw electric motor that does the acceleration for us.
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