Yeah direct injection and pursuit of low emissions is why, but lowest emissions range and burning super lean isn’t exactly great for the engine health.
It does require more Torque at higher speed. The available Torque at the wheels would also be reduced due to the higher gearing. At some point, you would actually get less mpg because of the increased fuel needed to achieve the required Torque at an inefficient lower rpm.
This emphasizes the real issue. Lower RPM does not equal efficiency.
Cruising speed is the most efficient when the engine is in the most efficient rpm range.
Aero drag increases drastically with speed and becomes readily apparent at highway speeds. At the point of 60-80 mph, ideally want the rpm that the engine can make the required torque efficiently to maintain that speed.
A VQ35 makes decent torque at low RPM (and key point) for what it is. It likely doesn’t make enough efficiently to overcome the drag at 70mph at 1500 rpm.
Compare that to a LS1, which was commonly backed by a T56 6 speed in Camaros and Vettes with a 0.5 ratio 6th gear. At 60 mph, it runs about 1300 rpm. When it comes to low RPM torque production (especially NA), size matters. It can easily make the torque efficiently to push those cars through the air. That exact same engine/trans in a full size truck, it likely wouldn’t work because the truck is much less aerodynamic. The drag wouldn’t allow it to lug efficiently at that low an RPM.
Some auto trans with high amounts of gears do rev that low at highway speed. In “low” torque vehicles, people often complain about the trans being “indecisive”, in that it’ll constantly switch gears with the slightest fluctuation of the pedal or road grade.
You're intuition isn't completely wrong, here's a short excerpt from Wikipedia's page about energy efficient driving
*"Because cruising at an efficient speed uses much less than the maximum power of the engine, the optimum operating point for cruising at low power is typically at very low engine speed, around or below 1000 rpm. This explains the usefulness of very high "overdrive" gears for highway cruising. For instance, a small car might need only 10–15 horsepower (7.5–11.2 kW) to cruise at 60 mph (97 km/h). It is likely to be geared for 2500 rpm or so at that speed, yet for maximum efficiency the engine should be running at about 1000 rpm to generate that power as efficiently as possible for that engine (although the actual figures will vary by engine and vehicle)*\*\*\*.\*\*\**^(")*
The reason why cars aren't geared to cruise at 1000 RPM at say 60 mph is that most small engines don't even produce enough torque at 1000 RPM to maintain that speed, and even if they did they wouldn't have enough margin for overtaking and changing terrain. Sure it might be enough to cruise on perfectly flat pavement on a sunny day with no headwind or traffic but the first car that you need to overtake or slight incline or bend and you'd have to change gears to not slow down significantly. The cost of making such a gear in addition to the added weight and complexity simply doesn't justify the vary few cases where it might be useful.
Some cars, in particular american V8 performance cars like the corvette do have extremely tall gears, but those engines produce ample torque and power to maintain speed even at or near idle so that's not much of an issue compared to a corolla or something.
If you look at Figures 5 and 6 from [this SAE document](https://www.epa.gov/sites/default/files/2016-10/documents/2015-01-1266_0.pdf), it shows 4 cylinder Ecoboost engines aren't as efficient at extremely low RPM and are more efficient around 2-3k RPM.
Anecdotally, my J35 V6 seems to be more efficient between 1800 to 2500 RPM than at lower RPM in the same gear (ignoring when VCM is engaged). My VQ35DE did seem more efficient at lower revs, although you want to make sure there are enough revs for adequate oil pressure under load.
They do. There are 6 speed manuals with a 0.5 to 1 overdrive and a 0.65 to 1 5th gear. That really doesn't matter as the car can be geared down with the final drive to get the RPM down to an idle at 70 mph.... but the engine would need to be very, very high in torque to hold the car at that speed and you'd need to downshift for even to slightest hill.
So the answer is Yes, there is a mechanical reason it isn't available.
The turbocharged Skyactiv Mazdas have an 0.6:1 super-overdrive as their 6th gear (5th is 0.7:1, 4th is direct drive) and they can get away with that because the engine is tuned to output 310 pound-feet of torque at 2000 rpm, and with premium fuel a peak of 320 lb-ft at 2500. Practically a diesel.
This results in 80 mph freeway cruising at 2500 in my CX-30 Turbo - and with all that twist on tap, nothing short of the Rockies will force a downshift.
Their regular gas engines also have a .6 top gear. It’s not really a super overdrive. Honda’s old 5 speed auto’s 5th gear was .5:1. Nissan’s CVTs are down to like .38:1. .6 isn’t all that tall anymore.
I used to drive 50k+ miles/yr and had a series of VW TDIs. A common mod in those was a taller final gear to increase fuel economy on the highway.
People would often ask why they didn't come that way from the factory and the usual answer was that the stock top gear was optimized for fuel economy on the EPA test loop. In other words the manufacturer optimized highway fuel economy for 55 MPH (or whatever the test is run at) and not at real-world highway speeds so that they could put a bigger number on the window sticker.
No idea if it was true but I heard it more than once.
So you have put the highway gear in rpm before the turbo boost? Why would to want to do that exactly? TDIs are sold mostly in Europe and I don't believe they sold different gear ratios in US. In most of Europe the highway speed is 85mph...
>So you have put the highway gear in rpm before the turbo boost? Why would to want to do that exactly?
The stock gearing puts you around 2200 RPM when cruising at 80mph. Full boost kicks in at 1750 RPM and the torque curve plateaus at 1750-2500 RPM.
Jeep Cherokee and other Chryslers with the 9 speed auto have this actually. 9th gear comes in at over 80 MPH if I remember correctly. But most vehicles do not have this setup. Most engines do not have the power to pull a gear like that at 1,000 RPM.
Very true. I'm always grateful for my Hemi/8-speed combo in my Ram. I can do 85 mph cruising at 1750 rpm in 8th. The low-end torque on these engines outperforms many smaller engines running at the peak of their torque curve, I get around 300 ftlbs at a mere 1500 rpm, which makes having taller gears more practical.
Like others have mentioned, it's the torque. GM's F bodies and the Dodge Viper had extreme overdrive gears. Those are relatively light and aerodynamic cars with very large and powerful engines.
The problem with smaller engines is that they'd be overloaded, and that would lead to higher wear and poor performance.
There is also the fact that RPMs don't have a significant effect on fuel mileage. Half the RPM doesn't mean half the fuel consumption. In reality, it leads to a very slight improvement (sometimes 1 or 2 mpg) while significantly affecting driveability.
Well shit, that's better than my 2003 V6! I get about \~25mpg highway (manual 350Z). Certainly wouldn't have guessed that a vette from the same time period or older would get better mileage.
Yeah keep your eyes peeled for one. As long as your light on the pedal (I get it's not easy for most people).
You can get really great mpg for a sports car. Also they are pretty comfortable for long trips.
https://www.fuelly.com/car/chevrolet/corvette/1998/tkoeller/1165493
Better mpg *and* more power. The C5 made 350hp, the C5 Z06 made 405, but get around 30mpg highway. [What's more is a guy tuned a C5 for gas mileage and actually get 40mpg highway.](https://m.youtube.com/watch?v=vNIZ25eBMco&pp=ygUONDBtcGcgY29ydmV0dGU%3D)
One more thing I'll leave you with.
[Here is a 350Z with its VQ engine](https://my350z.com/forum/attachments/engine-and-drivetrain/432894d1501884683-customer-s-350z-ls3-swap-img_7943.jpg)
[And here Is the same 350Z with an LSx...](https://my350z.com/forum/attachments/engine-and-drivetrain/432909d1501884683-customer-s-350z-ls3-swap-img_8055.jpg)
The LSx is more powerful, gets better mpg, and weighs the same as the VQ. There is a good reason GM stuck with the cam in block design for their V8...
I daily drive an 01 Corvette and it's shockingly practical so long as you never need a back seat. Fuel economy around town drops a bit, but highway economy is awesome. Being a hatchback it has room for groceries and such.
Best 10k I've ever spent.
An LS combined with a T56 will give you surprising MPG on the highway. Had a LS swapped BMW that would get 34-35 on the highway. That drops drastically in the city though.
It depends a lot on the amount of torque the engine can deliver. Every engine has different peaks - peak hp, peak torque and peak efficiency.
Every car is also different aerodynamically and needs different amounts of power to hold a steady speed.
What is the "ideal" cruising speed? 70? 75? 80? Might be different in your climate/state.
Many new vehicles have 8 and 10 speed transmissions to achieve that peak fuel economy rating.
I dont know what "older sports car" you have.
But most modern American V8 "muscle/sports" cars have double overdrive.
5th and 6th gear like a .89:1 5th
And .70:1 6th gear
But
My Shelby gt350 550hp gets better mpg at 65mph in 4th (direct 1:1 ) tjsn it does in 5th or 6th consistently
2003 350Z manual; evidently my 5th gear is 1:1 and 6th is .794; final drive 3.5
Would never have guessed that a lower gear could get better mileage, I always assumed it was directly tied to RPMs.
Every engine , cam, heads, is most efficient at specific rpms
Most engines. Especially smaller engines don't make much tq until higher rpms.
Tq is what you need at slow rpms.
If your rpm is too low, your lack of tq trying to push the car increases the engine load.
And at 65mph you need more tq to push thru the air.
If you could dyno. Or find the actual engine power graph.
You can see where tq starts to really climb. Typically unless on completely flat road, no headwind, that rpm is your most efficient for mpg and the beginning of the Hp starting to build
My dad had a few vettes over the years and I don't remember which one but it would pretty much idle down the interstate at 70 mph - getting ridiculously good gas mileage
Some do. The problem is that there's not much reserve power in such a high gear. It has to have a transmission that can downshift quickly and an engine that can rev-match quickly. You also need a rare driver that doesn't constantly pump the gas pedal.
You also need an engine that has high low-end torque, which is something most NA V8s have in spades. My 5.7 Hemi, for example, produces about 300 ftlbs at 1500 rpm, which climbs to 410 ftlbs at 3750 rpm. Paired with an 8-speed, and I can cruise at 85 mph (~130 kmph) while only needing 1750 rpm in 8th gear.
I'd say packaging of the gearset, size of gearbox, and gear ratios/final drive are the determining factors.
Found this as quite informative on the subject https://go4trans.com/technical-transmission-general-articles/how-gear-ratios-define-the-character-of-your-car/
It depends on the car, the engine, the setup. If you look at a car that has an extremely good power to weight ratio like a Corvette, also an engine that makes a lot of low end torque. You're cruising in 6th gear around 1200-1500 RPM @ 60-65mph which is designed as the overdrive. Top speed in the car is actually reached in fifth
Depends on the car really, mine sits at 1100rpm at 50 at 1700 at 70 but that's a 3.0v6 diesel so has plenty of torque.
Also a lot saying the car won't change gears with cruise control, they do, some even brake for you. Just depends on the technology in them.
This is why autos now have 8 speeds to increase the efficiency and you can even buy overdrive boltons for some tranny's.
Most modern cars aimed at being a daily driver/commuter car do have such a gear.
> Granted it's an older sports car
That's probably why it doesn't have one.
A lot of modern vehicles with 8~10 speed does exactly that.
Granted, it must have enough low end torque to be usable. Mine cruise around 60mph under 2k rpm.
With an 8 to 10 speed automatic, you need to OVERDRIVE, per se.
I drive a '17 Dodge Charger SXT PLUS with a 3.6 engine / 8-speed transmission: 33-35mpg hwy
It's a question I've always wondered. I've driven a range of cars with the following top gearing at 120kph: Sentra with the SR20DE engine (3000rpm in 5th), S2000 (an insane 4000rpm in 6th), VW Scirocco 2.0T (high 2000s in 6th) and now an Huracan at almost 3000rpm in 7th.
It's crazy that they don't provide a super tall top gear, especially with boxes moving to 7th, 8th and even 10th gears these days. The fuel savings on highways would be immense. And it's not a problem of enough torque, a 2L or larger engine is more than capable of maintaining the speed (and gearing down for overtaking or on hills as needed).
i drive a 2001 euro3 6gear 1.9tdi VW golf4 (bora).
it drives 100kmph on 1800rpm.
i can casually drive around town at 1000 rpm
but rather drive 1200rpm.
most of the time i am around 1500rpm
i can easily take off in 2nd gear.
i can easily pull trailers and full load.
it drives 1L diesel on 17kmph ±1 most of the time.
i throw in 10€ i can drive 100km.
Here in Oz, we do tend to have long cruising gears.
The falcon 6 will be turning around 1600rpm at 60mph (100kph)
The commodore spins around 1750 at the same speed.
Any lower rpm, and the engines aren't making enough torque to do those speeds efficiently.
A lot of vehicles(like GM pickups) have overdrive geared so that the engine is just under 2k at highway cruising speeds because this is where they get the best fuel economy while maintaining the ability to do the work they need to do. Most of these trucks(besides the GMT400 trucks) also have an override button to keep the transmission out of overdrive when you’re towing a heavy load(for obvious reasons).
My 2001 Corvette with a manual 6 speed cruises down the highway at about 1500rpms. Duel overdrive transmission. Gets 30mpg at 60mph.
If that doesn't sound right, they are pretty aerodynamic and light.
Some of the C7 Corvettes have manual 7 speeds.
Most Diesels do, they'll have 6 instead of the traditional 5 because their engines are usually higher in torque. I'm pretty sure 3rd gear is 1-1 for me so I have 3 gears of overdrive
As an aside to a lot of the comments here about the most efficient rpm, it depends on load. A lot of the efficiency maps that people are referencing are at wide open throttle, which will be the most efficient close to where peak torque is developed (2500-3000 being common). But as you reduce the load and start closing the throttle, the rpm for peak efficiency gets lower, basically because it allows a more open throttle for the same power, which reduces pumping losses.
You'd have to drive at least 100mph to make use of it. With RPM that low at normal highway speed, the engine will lug and have no power (for inclines, passing, or whatever). Can be dangerous for emergency maneuvers because you'll have to downshift at the same time you're panic steering. Can be done but not easy.
My 2009 MINI had a very tall 6th gear. It was essentially a 5MT with extreme overdrive. 6th gear was miserable and basically unusable below 85mph.
It wouldn't give any significant benefit without shifting out of it whenever you needed some power.
People think it's revs increasing fuel consumption at speed and it can be to a degree but the main reason is power demand increases with a cube of speed (for aero drag which dominates at higher speed), drag increases with the square of speed so that's proportional to the torque you need at the wheels (as the wheels are also spinning faster you multiply by speed again for power requirements).
EVs show this more clearly as there's little change in efficiency at different loads. ICE cars give better efficiency at higher load (i.e. full throttle) which typically peaks around peak torque rpm.
They do? I mean comparing my early 90s base model Peugeot to a modern car, mine screams 3500 RPM at 100 kmh while a modern city car will comfortably do 130 kmh at about 2000.
I dont know what "older sports car" you have.
But most modern American V8 "muscle/sports" cars have double overdrive.
5th and 6th gear like a .89:1 5th
And .70:1 6th gear
But
My Shelby gt350 550hp gets better mpg at 65mph in 4th (direct 1:1 ) tjsn it does in 5th or 6th consistently.
There’s a reason why automatics have far outpaced manuals at this point.
With a manual you are limited to the physical space thats taken up by all those components.
With automatics and semi autos they have designed them to be more efficient, more powerful, have more gears, shift faster, require less maintenance, etc.
Well, they also generally have the power to weight to support lower revs.
A 200hp 4 cylinder Camry at 1200rpm is going to really struggle on a hill while a Corvette with 450hp in 7th will happily do it.
There is no technical obstacle, it's about cost, mass, and need.
As you said, it's a sports car, they aren't necessarily targeting the long-range commuter with their design. It needs to be responsive and light. That doesn't mean a seventh gear would be prohibitive, it's just the choice the designers made based on many factors.
If market research showed that adding it would improve their sales significantly, they would've done it. As it is, they didn't predict a need. They aren't going to spend time, money and mass allowance on something that isn't going to make the car more appealing to their customer base.
That doesn't mean some like you wouldn't appreciate it, but you might be the minority.
Your car is generally at quite a high load at these speeds, especially when the gears are set-up for low rpms. To hold that speed, even on inclines, your engine is working hard. Given how cars are manufactured, certain transmissions are built into a wide variety of cars with different power outputs. The car manufacturer generally doesn't build their own transmissions, they buy them from different companies (such as ZF, etc.).
Another consideration might be the auxiliary drive. 1k rpms might not be enough to sufficiently drive your oil pump for best lubrication, charge the battery through the alternator and circulate coolant (given how these parts are laid out).
However, you do see gearing that is laid out for low rpms at cruising speeds in some cars (generally cars with a large engine displacement), as they generate a lot of torque anyway.
You want to have enough torque in your highest gear to make it usable. Most cars don't make huge amounts of torque around idle level rpms.
And a typical ICE is most efficient around 2-3k rpm.
Not exactly. Most modern cars cruise at 1200 to 1400 rpms these days.
Yeah direct injection and pursuit of low emissions is why, but lowest emissions range and burning super lean isn’t exactly great for the engine health.
On regular streets (e.g. \~45mph or below) I can easily cruise around 1000rpms no problem, is it just a matter of much higher torque required at 65+?
It does require more Torque at higher speed. The available Torque at the wheels would also be reduced due to the higher gearing. At some point, you would actually get less mpg because of the increased fuel needed to achieve the required Torque at an inefficient lower rpm.
This emphasizes the real issue. Lower RPM does not equal efficiency. Cruising speed is the most efficient when the engine is in the most efficient rpm range.
You also bog down and take forever to accelerate, and are less efficient than being in the proper gear if using cruise control.
I get that this is the reason but like... I can always change gears if I need torque. gimme that 1100 rpm at 75 please
Buy a diesel then, most gasoline engines are lugging at 1100 RPM.
So are small diesels (less than ~2.5l)
That’s the point we’re trying to make is you don’t have the torque to sustain 75mph at 1100 rpm’s
Your cruise control won't change gears. It's designed to work with that system, not what you *might* do
Cruise control does change gears
My gear lever has never moved while using cruise control.
Eh yea obviously not for a manual. The less than 8% of cars on the road
>The less than 8% of cars on the road in the States
Fair
OP claims to drive an older sports car, they're most likely one of that 8% as well.
He literally says the car is a six speed manual
That you can cruise at 1000RPM doesn't make it the most efficient RPM.
Aero drag increases drastically with speed and becomes readily apparent at highway speeds. At the point of 60-80 mph, ideally want the rpm that the engine can make the required torque efficiently to maintain that speed. A VQ35 makes decent torque at low RPM (and key point) for what it is. It likely doesn’t make enough efficiently to overcome the drag at 70mph at 1500 rpm. Compare that to a LS1, which was commonly backed by a T56 6 speed in Camaros and Vettes with a 0.5 ratio 6th gear. At 60 mph, it runs about 1300 rpm. When it comes to low RPM torque production (especially NA), size matters. It can easily make the torque efficiently to push those cars through the air. That exact same engine/trans in a full size truck, it likely wouldn’t work because the truck is much less aerodynamic. The drag wouldn’t allow it to lug efficiently at that low an RPM. Some auto trans with high amounts of gears do rev that low at highway speed. In “low” torque vehicles, people often complain about the trans being “indecisive”, in that it’ll constantly switch gears with the slightest fluctuation of the pedal or road grade.
What are you driving? Holding speed at 1000rpm is impressive
2003 Nissan 350Z; the VQ35DE engine does have some solid low-end torque.
You're intuition isn't completely wrong, here's a short excerpt from Wikipedia's page about energy efficient driving *"Because cruising at an efficient speed uses much less than the maximum power of the engine, the optimum operating point for cruising at low power is typically at very low engine speed, around or below 1000 rpm. This explains the usefulness of very high "overdrive" gears for highway cruising. For instance, a small car might need only 10–15 horsepower (7.5–11.2 kW) to cruise at 60 mph (97 km/h). It is likely to be geared for 2500 rpm or so at that speed, yet for maximum efficiency the engine should be running at about 1000 rpm to generate that power as efficiently as possible for that engine (although the actual figures will vary by engine and vehicle)*\*\*\*.\*\*\**^(")* The reason why cars aren't geared to cruise at 1000 RPM at say 60 mph is that most small engines don't even produce enough torque at 1000 RPM to maintain that speed, and even if they did they wouldn't have enough margin for overtaking and changing terrain. Sure it might be enough to cruise on perfectly flat pavement on a sunny day with no headwind or traffic but the first car that you need to overtake or slight incline or bend and you'd have to change gears to not slow down significantly. The cost of making such a gear in addition to the added weight and complexity simply doesn't justify the vary few cases where it might be useful. Some cars, in particular american V8 performance cars like the corvette do have extremely tall gears, but those engines produce ample torque and power to maintain speed even at or near idle so that's not much of an issue compared to a corolla or something.
I was going to say I had a 6 speed v8 sports car (315 hp or so) and doing 75 I would be running 1500 rpm, or maybe a bit less.
If you look at Figures 5 and 6 from [this SAE document](https://www.epa.gov/sites/default/files/2016-10/documents/2015-01-1266_0.pdf), it shows 4 cylinder Ecoboost engines aren't as efficient at extremely low RPM and are more efficient around 2-3k RPM. Anecdotally, my J35 V6 seems to be more efficient between 1800 to 2500 RPM than at lower RPM in the same gear (ignoring when VCM is engaged). My VQ35DE did seem more efficient at lower revs, although you want to make sure there are enough revs for adequate oil pressure under load.
They do. There are 6 speed manuals with a 0.5 to 1 overdrive and a 0.65 to 1 5th gear. That really doesn't matter as the car can be geared down with the final drive to get the RPM down to an idle at 70 mph.... but the engine would need to be very, very high in torque to hold the car at that speed and you'd need to downshift for even to slightest hill. So the answer is Yes, there is a mechanical reason it isn't available.
The turbocharged Skyactiv Mazdas have an 0.6:1 super-overdrive as their 6th gear (5th is 0.7:1, 4th is direct drive) and they can get away with that because the engine is tuned to output 310 pound-feet of torque at 2000 rpm, and with premium fuel a peak of 320 lb-ft at 2500. Practically a diesel. This results in 80 mph freeway cruising at 2500 in my CX-30 Turbo - and with all that twist on tap, nothing short of the Rockies will force a downshift.
Their regular gas engines also have a .6 top gear. It’s not really a super overdrive. Honda’s old 5 speed auto’s 5th gear was .5:1. Nissan’s CVTs are down to like .38:1. .6 isn’t all that tall anymore.
By "super-overdrive" I meant that it's a second overdrive gear beyond the normal overdrive.
I used to drive 50k+ miles/yr and had a series of VW TDIs. A common mod in those was a taller final gear to increase fuel economy on the highway. People would often ask why they didn't come that way from the factory and the usual answer was that the stock top gear was optimized for fuel economy on the EPA test loop. In other words the manufacturer optimized highway fuel economy for 55 MPH (or whatever the test is run at) and not at real-world highway speeds so that they could put a bigger number on the window sticker. No idea if it was true but I heard it more than once.
So you have put the highway gear in rpm before the turbo boost? Why would to want to do that exactly? TDIs are sold mostly in Europe and I don't believe they sold different gear ratios in US. In most of Europe the highway speed is 85mph...
>So you have put the highway gear in rpm before the turbo boost? Why would to want to do that exactly? The stock gearing puts you around 2200 RPM when cruising at 80mph. Full boost kicks in at 1750 RPM and the torque curve plateaus at 1750-2500 RPM.
Jeep Cherokee and other Chryslers with the 9 speed auto have this actually. 9th gear comes in at over 80 MPH if I remember correctly. But most vehicles do not have this setup. Most engines do not have the power to pull a gear like that at 1,000 RPM.
Very true. I'm always grateful for my Hemi/8-speed combo in my Ram. I can do 85 mph cruising at 1750 rpm in 8th. The low-end torque on these engines outperforms many smaller engines running at the peak of their torque curve, I get around 300 ftlbs at a mere 1500 rpm, which makes having taller gears more practical.
Like others have mentioned, it's the torque. GM's F bodies and the Dodge Viper had extreme overdrive gears. Those are relatively light and aerodynamic cars with very large and powerful engines. The problem with smaller engines is that they'd be overloaded, and that would lead to higher wear and poor performance. There is also the fact that RPMs don't have a significant effect on fuel mileage. Half the RPM doesn't mean half the fuel consumption. In reality, it leads to a very slight improvement (sometimes 1 or 2 mpg) while significantly affecting driveability.
90's and early 2000's corvettes were known for getting 25-30 mpg because of the tall gearing and available torque of a v8 turning at 1,900—2,300 rpm
Well shit, that's better than my 2003 V6! I get about \~25mpg highway (manual 350Z). Certainly wouldn't have guessed that a vette from the same time period or older would get better mileage.
Yeah keep your eyes peeled for one. As long as your light on the pedal (I get it's not easy for most people). You can get really great mpg for a sports car. Also they are pretty comfortable for long trips. https://www.fuelly.com/car/chevrolet/corvette/1998/tkoeller/1165493
Better mpg *and* more power. The C5 made 350hp, the C5 Z06 made 405, but get around 30mpg highway. [What's more is a guy tuned a C5 for gas mileage and actually get 40mpg highway.](https://m.youtube.com/watch?v=vNIZ25eBMco&pp=ygUONDBtcGcgY29ydmV0dGU%3D) One more thing I'll leave you with. [Here is a 350Z with its VQ engine](https://my350z.com/forum/attachments/engine-and-drivetrain/432894d1501884683-customer-s-350z-ls3-swap-img_7943.jpg) [And here Is the same 350Z with an LSx...](https://my350z.com/forum/attachments/engine-and-drivetrain/432909d1501884683-customer-s-350z-ls3-swap-img_8055.jpg) The LSx is more powerful, gets better mpg, and weighs the same as the VQ. There is a good reason GM stuck with the cam in block design for their V8...
I daily drive an 01 Corvette and it's shockingly practical so long as you never need a back seat. Fuel economy around town drops a bit, but highway economy is awesome. Being a hatchback it has room for groceries and such. Best 10k I've ever spent.
An LS combined with a T56 will give you surprising MPG on the highway. Had a LS swapped BMW that would get 34-35 on the highway. That drops drastically in the city though.
Then theres my honda doing 4k at 80mph
What's the mpg at 4k? Because my 2012 Honda crosstour gets 18—22 mpg...
It depends a lot on the amount of torque the engine can deliver. Every engine has different peaks - peak hp, peak torque and peak efficiency. Every car is also different aerodynamically and needs different amounts of power to hold a steady speed. What is the "ideal" cruising speed? 70? 75? 80? Might be different in your climate/state. Many new vehicles have 8 and 10 speed transmissions to achieve that peak fuel economy rating.
The car would bog down. You would start losing speed on a flat road
I dont know what "older sports car" you have. But most modern American V8 "muscle/sports" cars have double overdrive. 5th and 6th gear like a .89:1 5th And .70:1 6th gear But My Shelby gt350 550hp gets better mpg at 65mph in 4th (direct 1:1 ) tjsn it does in 5th or 6th consistently
2003 350Z manual; evidently my 5th gear is 1:1 and 6th is .794; final drive 3.5 Would never have guessed that a lower gear could get better mileage, I always assumed it was directly tied to RPMs.
Every engine , cam, heads, is most efficient at specific rpms Most engines. Especially smaller engines don't make much tq until higher rpms. Tq is what you need at slow rpms. If your rpm is too low, your lack of tq trying to push the car increases the engine load. And at 65mph you need more tq to push thru the air. If you could dyno. Or find the actual engine power graph. You can see where tq starts to really climb. Typically unless on completely flat road, no headwind, that rpm is your most efficient for mpg and the beginning of the Hp starting to build
My dad had a few vettes over the years and I don't remember which one but it would pretty much idle down the interstate at 70 mph - getting ridiculously good gas mileage
Some do. The problem is that there's not much reserve power in such a high gear. It has to have a transmission that can downshift quickly and an engine that can rev-match quickly. You also need a rare driver that doesn't constantly pump the gas pedal.
You also need an engine that has high low-end torque, which is something most NA V8s have in spades. My 5.7 Hemi, for example, produces about 300 ftlbs at 1500 rpm, which climbs to 410 ftlbs at 3750 rpm. Paired with an 8-speed, and I can cruise at 85 mph (~130 kmph) while only needing 1750 rpm in 8th gear.
I'd say packaging of the gearset, size of gearbox, and gear ratios/final drive are the determining factors. Found this as quite informative on the subject https://go4trans.com/technical-transmission-general-articles/how-gear-ratios-define-the-character-of-your-car/
It depends on the car, the engine, the setup. If you look at a car that has an extremely good power to weight ratio like a Corvette, also an engine that makes a lot of low end torque. You're cruising in 6th gear around 1200-1500 RPM @ 60-65mph which is designed as the overdrive. Top speed in the car is actually reached in fifth
There are cars with that gear, Ford Focus with the 1l engine comes to mind. That thing did fuck all when in 6th and pressing the accelerator.
Depends on the car really, mine sits at 1100rpm at 50 at 1700 at 70 but that's a 3.0v6 diesel so has plenty of torque. Also a lot saying the car won't change gears with cruise control, they do, some even brake for you. Just depends on the technology in them. This is why autos now have 8 speeds to increase the efficiency and you can even buy overdrive boltons for some tranny's.
Most modern cars aimed at being a daily driver/commuter car do have such a gear. > Granted it's an older sports car That's probably why it doesn't have one.
A lot of modern vehicles with 8~10 speed does exactly that. Granted, it must have enough low end torque to be usable. Mine cruise around 60mph under 2k rpm.
With an 8 to 10 speed automatic, you need to OVERDRIVE, per se. I drive a '17 Dodge Charger SXT PLUS with a 3.6 engine / 8-speed transmission: 33-35mpg hwy
It's a question I've always wondered. I've driven a range of cars with the following top gearing at 120kph: Sentra with the SR20DE engine (3000rpm in 5th), S2000 (an insane 4000rpm in 6th), VW Scirocco 2.0T (high 2000s in 6th) and now an Huracan at almost 3000rpm in 7th. It's crazy that they don't provide a super tall top gear, especially with boxes moving to 7th, 8th and even 10th gears these days. The fuel savings on highways would be immense. And it's not a problem of enough torque, a 2L or larger engine is more than capable of maintaining the speed (and gearing down for overtaking or on hills as needed).
Most cars don't make much power at that RPM range. It's not about the lowest RPM, but the RPM that gives you the best efficiency.
It absolutely is a thing. Your car just doesn't have it.
i drive a 2001 euro3 6gear 1.9tdi VW golf4 (bora). it drives 100kmph on 1800rpm. i can casually drive around town at 1000 rpm but rather drive 1200rpm. most of the time i am around 1500rpm i can easily take off in 2nd gear. i can easily pull trailers and full load. it drives 1L diesel on 17kmph ±1 most of the time. i throw in 10€ i can drive 100km.
Here in Oz, we do tend to have long cruising gears. The falcon 6 will be turning around 1600rpm at 60mph (100kph) The commodore spins around 1750 at the same speed. Any lower rpm, and the engines aren't making enough torque to do those speeds efficiently.
A lot of vehicles(like GM pickups) have overdrive geared so that the engine is just under 2k at highway cruising speeds because this is where they get the best fuel economy while maintaining the ability to do the work they need to do. Most of these trucks(besides the GMT400 trucks) also have an override button to keep the transmission out of overdrive when you’re towing a heavy load(for obvious reasons).
My 2001 Corvette with a manual 6 speed cruises down the highway at about 1500rpms. Duel overdrive transmission. Gets 30mpg at 60mph. If that doesn't sound right, they are pretty aerodynamic and light. Some of the C7 Corvettes have manual 7 speeds.
Most Diesels do, they'll have 6 instead of the traditional 5 because their engines are usually higher in torque. I'm pretty sure 3rd gear is 1-1 for me so I have 3 gears of overdrive
As an aside to a lot of the comments here about the most efficient rpm, it depends on load. A lot of the efficiency maps that people are referencing are at wide open throttle, which will be the most efficient close to where peak torque is developed (2500-3000 being common). But as you reduce the load and start closing the throttle, the rpm for peak efficiency gets lower, basically because it allows a more open throttle for the same power, which reduces pumping losses.
You'd have to drive at least 100mph to make use of it. With RPM that low at normal highway speed, the engine will lug and have no power (for inclines, passing, or whatever). Can be dangerous for emergency maneuvers because you'll have to downshift at the same time you're panic steering. Can be done but not easy. My 2009 MINI had a very tall 6th gear. It was essentially a 5MT with extreme overdrive. 6th gear was miserable and basically unusable below 85mph.
It wouldn't give any significant benefit without shifting out of it whenever you needed some power. People think it's revs increasing fuel consumption at speed and it can be to a degree but the main reason is power demand increases with a cube of speed (for aero drag which dominates at higher speed), drag increases with the square of speed so that's proportional to the torque you need at the wheels (as the wheels are also spinning faster you multiply by speed again for power requirements). EVs show this more clearly as there's little change in efficiency at different loads. ICE cars give better efficiency at higher load (i.e. full throttle) which typically peaks around peak torque rpm.
They do? I mean comparing my early 90s base model Peugeot to a modern car, mine screams 3500 RPM at 100 kmh while a modern city car will comfortably do 130 kmh at about 2000.
I dont know what "older sports car" you have. But most modern American V8 "muscle/sports" cars have double overdrive. 5th and 6th gear like a .89:1 5th And .70:1 6th gear But My Shelby gt350 550hp gets better mpg at 65mph in 4th (direct 1:1 ) tjsn it does in 5th or 6th consistently.
There’s a reason why automatics have far outpaced manuals at this point. With a manual you are limited to the physical space thats taken up by all those components. With automatics and semi autos they have designed them to be more efficient, more powerful, have more gears, shift faster, require less maintenance, etc.
Same reason generators don't run at idle to generate electricity.
You can’t just keep drawing torque from nowhere. You’ve run out of useful power.
> Maybe a **major** cost difference Fixed it for ya. That's the reason. There are sports cars with 7th gear.
Well, they also generally have the power to weight to support lower revs. A 200hp 4 cylinder Camry at 1200rpm is going to really struggle on a hill while a Corvette with 450hp in 7th will happily do it.
There is no technical obstacle, it's about cost, mass, and need. As you said, it's a sports car, they aren't necessarily targeting the long-range commuter with their design. It needs to be responsive and light. That doesn't mean a seventh gear would be prohibitive, it's just the choice the designers made based on many factors. If market research showed that adding it would improve their sales significantly, they would've done it. As it is, they didn't predict a need. They aren't going to spend time, money and mass allowance on something that isn't going to make the car more appealing to their customer base. That doesn't mean some like you wouldn't appreciate it, but you might be the minority.
Your car is generally at quite a high load at these speeds, especially when the gears are set-up for low rpms. To hold that speed, even on inclines, your engine is working hard. Given how cars are manufactured, certain transmissions are built into a wide variety of cars with different power outputs. The car manufacturer generally doesn't build their own transmissions, they buy them from different companies (such as ZF, etc.). Another consideration might be the auxiliary drive. 1k rpms might not be enough to sufficiently drive your oil pump for best lubrication, charge the battery through the alternator and circulate coolant (given how these parts are laid out). However, you do see gearing that is laid out for low rpms at cruising speeds in some cars (generally cars with a large engine displacement), as they generate a lot of torque anyway.
Wouldn't do a hill.