A 2.5 altima with a CVT rental we got a few years ago got better mileage @ 84 vs 75 cruise settings. 75 was a consistent 35 mpg vs fresh tank @ 84 was pushing 39. I wanted to attempt a bit faster test but SWMBO was already going on about "not getting a ticket".
ProDarwin said:Wind resistance increases with the square of velocity.
Road load power increases with the cube of velocity.
As a result I'm highly skeptical of anyone who says their peak economy is at a speed higher than 1500(ish) RPM in their highest gear.
For example, the WR on a car at 78mph is 53% higher than 65mph. The power requirement at 78mph is 73% higher than at 65mph. Engine tuning can well be a factor, but I have doubts that any production engine nearly doubles its efficiency 20% higher in the powerband.
Similarly, go on EcoModder and ask how many people are driving at 70, 80 or 90mph to achieve their best economy. The answer is zero.
FDrx-7 get's better mileage @ 80+mph vs 70. Car get's into a happy groove right around 90mph and just likes to cruise.
In reply to Mr. Lee :
I think that's missing the point.
One can not argue the physics of aero and road drag. They go up faster than you speed does.
So IF you car gets better mileage at higher speeds/loads, one needs more to understand why it's better. It's not normal for engines to be that much more efficient when you get past the nominal speed range for most cars. So something is wrong at the lower speed. What it is- that's hard to say without data. But for sure, something is up.
I've never come across an normal production engine that has it's best efficiency point much more than 2300rpm, and on a pretty conservatively geared car, that will be about 70 mph. Most cars will be above that at 70. Let alone 90. So if you are getting better mileage the faster you are going (which I'm not doubting is possible), something is wrong at the lower speeds. Or at least not correct.
You know, the FD RX-7 engine setup was pretty odd, so it wouldn't surprise me at all that things weren't quite "right" down low in the rev range during cruise.
alfadriver said:I've never come across an normal production engine that has it's best efficiency point much more than 2300rpm, and on a pretty conservatively geared car, that will be about 70 mph. Most cars will be above that at 70. Let alone 90. So if you are getting better mileage the faster you are going (which I'm not doubting is possible), something is wrong at the lower speeds. Or at least not correct.
Yes. And what I was trying to point out was that even if you are right at peak engine efficiency, the lower power requirements of lower speeds almost always outweigh the difference in efficiency and result in better fuel economy. Notice how much engine efficiency changes over the course of RPM when loaded with typical vehicle road loads (dotted line) - very little.
Random engine BSFC:
I can't find a rotary BSFC, but I highly doubt its very far off this in terms of shape.
pres589 said:You know, the FD RX-7 engine setup was pretty odd, so it wouldn't surprise me at all that things weren't quite "right" down low in the rev range during cruise.
It may be, but comparing 60mph with ~85- that's at least double the drag. To get better mileage at 85, using double the power, you need a huge increase of efficiency. If efficiency kept constant, fuel economy would drop at the higher speed because you would use double the fuel to go only 42% faster. So you need the engine efficiency to increase to just make up for that, let alone another increase to make the improvement.
Even for an rotary engine, that doesn't make sense.
So if you really make better fuel economy at that much higher speeds, what is going on at the lower speeds to explain why? The point isn't that the improvement is impossible, it's that something else is going on for that to happen. And what is that?
^all that.
Also, alfa, remember double drag != double power. Power varies with the cube of velocity.
Power = force x velocity.
That MPG observation was made on a road trip from Tampa, FL to NW Arkansas. I noted that that I was getting upper teens/low 20's on tanks where I kept the speeds down vs when I said "berk it let her run" and set the cruise at just shy of 90, which netted me upper 20's. (quick math in my head at the pump). This was 19 years ago, so I didn't pay attention to cruising rpm as much as I do now, but I want to say that put me right at 4k rpm cruising.
I did note using the cruise control @ 70, hills would slow the car way down before it suddenly caught up, vs @ 90 it just rolled up the hill and went about it's business. As my passenger noted, the car is just seemed happier @ 90 vs 70. No muss no fuss, just response and acceleration when asked for.
The0retical said:spandak said:From my experience you're probably best avoiding anything with a turbo. 90 mph in my MS3 is getting close to boost. Mileage drops off fast at that point.
Something that's slippery and has a motor that doesn't mind running higher in the rev range should serve you well. While I have no experience with anything from Tesla I know a Leaf loses power fast on a highway. Like 20% of its estimated mileage disappears.
Missed this the first time around. My MS3 is modified to the point where it's quick enough but reliable enough not to risk popping the motor (probably.) On BFG Sport Comp-2's it'll return 33 MPG doing 75 on cruise through a fairly hilly area. I suspect I could have the tuner lean out the tune and hold off the boost a bit longer. Combined with swapping the tires to a lesser rolling resistance setup I bet I could get 36 or so at that 75 and low 30's at 90.
I don't think I'd want to commute 180 miles day in it the way it's setup right now though but when it was more stockish it would certainly have been ok.
Gonna sneak in and ask how you do that? Mine is stock other than an intake. I can manage lowww 30s if I stay around 70-75 and keep cruise control off. Anything about 70 with cruise control and my mileage drops off predictably. Last road trip I did 70 with cruise and got 27mpg over the first tank. On the way back I was doing 75-80 with no cruise and averaged 29 I think? I'm on BFGs Comp 2 A/S. the sports were incredible but were gone in 15k. Nope.
I honestly think the c5 might be your best option. They get great mpg at high speeds in stock form. There’s a lot of drag to be lost by just switching the tires to something skinnier and low rolling resistance as the stock ones aren’t designed for I think. Also, you could easily go faster than 90 if you wanted and save even more time. I completely understand the logic of driving faster to get more time at home.
My personal experience was;
2011 Elantra GLS manual, got 39/40 every tank but when I maintained a constant 73 mph driving to Florida it got 43 mpg.
2017 Ioniq Hybrid auto, regularly gets 55/57 mpg per tank but at 70 mph it definitely drops to 50.
I have not travelling to Florida in it yet. I do drive long distances and the car has 27k on it since July
Mr. Lee said:That MPG observation was made on a road trip from Tampa, FL to NW Arkansas. I noted that that I was getting upper teens/low 20's on tanks where I kept the speeds down vs when I said "berk it let her run" and set the cruise at just shy of 90, which netted me upper 20's. (quick math in my head at the pump). This was 19 years ago, so I didn't pay attention to cruising rpm as much as I do now, but I want to say that put me right at 4k rpm cruising.
I did note using the cruise control @ 70, hills would slow the car way down before it suddenly caught up, vs @ 90 it just rolled up the hill and went about it's business. As my passenger noted, the car is just seemed happier @ 90 vs 70. No muss no fuss, just response and acceleration when asked for.
Something to figure into the calculations for those of you saying this makes no sense. He's burning a certain amount of fuel per hour no matter what but at 90 his miles covered is much greater than at 70 per each of those gallons. So even if the fuel rate going into the engine is slightly higher at the higher speed, the greater distance covered more than makes up for it.
I hope this makes sense, I'm having a hard time explaining myself without doing the time/distance/fuel math.
I'm thinking it had more to do with the rotary with boost in the equation. At 4k the change over to the second turbo is ready to happen, but at a steady state cruise there is no load to build boost with, so everything is happily spinning along. (right at roughly 4k is generally the torque peak for most stock port rotaries) but at that speed, everything is spooled up, just not creating boost. As soon as a load hits the motor, boost builds, and you have instant on demand power hence why hills didn't bother it as much at the higher speed. (that and it takes more to slow down a 90mph object vs a 70mph object) Add in Slippery body shap/low frontal area and it should get better mileage. but thanks to a motor that never stops firing large injectors, and the siren song of boost it's not so easy to get decent mpg from it.
That is my take on it, and my observations from my time with that wonderful machine. Now if I could just find one cheap to start playing with now that I've been to the school of spinning triangles. Piss poor tuning advice, and being young with lots of expendable income. I went through 3 motors in ~8 months after I started messing with it. I miss that car....
In reply to KyAllroad (Jeremy) :
That makes sense, except the assumption about constant fuel rate per time for 70 and 90. The increase in power required is more than that.
What is happening is that his engine is running poorly at 70 vs 90.
Not saying that it’s impossible by any means.
aussiesmg said:My personal experience was;
2011 Elantra GLS manual, got 39/40 every tank but when I maintained a constant 73 mph driving to Florida it got 43 mpg.
2017 Ioniq Hybrid auto, regularly gets 55/57 mpg per tank but at 70 mph it definitely drops to 50.
I have not travelling to Florida in it yet. I do drive long distances and the car has 27k on it since July
how do you like the ioniq? do the rear seats fold flat? Also does the AC run off the battery or is it engine driven?
spandak said:The0retical said:spandak said:From my experience you're probably best avoiding anything with a turbo. 90 mph in my MS3 is getting close to boost. Mileage drops off fast at that point.
Something that's slippery and has a motor that doesn't mind running higher in the rev range should serve you well. While I have no experience with anything from Tesla I know a Leaf loses power fast on a highway. Like 20% of its estimated mileage disappears.
Missed this the first time around. My MS3 is modified to the point where it's quick enough but reliable enough not to risk popping the motor (probably.) On BFG Sport Comp-2's it'll return 33 MPG doing 75 on cruise through a fairly hilly area. I suspect I could have the tuner lean out the tune and hold off the boost a bit longer. Combined with swapping the tires to a lesser rolling resistance setup I bet I could get 36 or so at that 75 and low 30's at 90.
I don't think I'd want to commute 180 miles day in it the way it's setup right now though but when it was more stockish it would certainly have been ok.
Gonna sneak in and ask how you do that? Mine is stock other than an intake. I can manage lowww 30s if I stay around 70-75 and keep cruise control off. Anything about 70 with cruise control and my mileage drops off predictably. Last road trip I did 70 with cruise and got 27mpg over the first tank. On the way back I was doing 75-80 with no cruise and averaged 29 I think? I'm on BFGs Comp 2 A/S. the sports were incredible but were gone in 15k. Nope.
The tune I have on the car is a fully custom one from Stratified Automotive Controls using the Accessport 3. The MS3 runs pretty rich on both the stock or off the shelf tunes to help prevent detonation. I the tuner I was working with remapped the fuel, air and boost tables to match my desired goals for the car. Since I drive the car pretty much every day there isn't snow on the ground I asked him to ensure it was reliable and I was aiming for 300 to 325 to the wheels. We were able to get the numbers and have the car remain reliable.
The initial tunes were producing gas mileage in the mid 20's due to how conservative they were but by the time we were done I was seeing right around 33 mpg going from the Poconos to Lancaster and back on the highway. It's a process and you'll need to decide where you're going to go with modifications to the car before you go down that road since it's not exactly cheap and you'll end up replacing a lot of parts again and again if you don't plan ahead.
Well obviously the answer is a plymouth superbird replica with its drag coefficient of .28, slammed down with some sort of hotted up mercedes diesel engine and a 6 speed and long legs.
Really my only comment is about the speed. I'm not 100% sure of how long ago it was, but I was going to Arizona with a relative, we hit rt 44 in Missouri, and everyone was doing 90. At least. Everyone was keeping right, there was no backup, no issues, no shiny happy people diving in between cars to make that extra minute on their commute and everyone was doing 30-40 mph over what they would be on I-95 while leaving a major city. The difference between that and the bullE36 M3 you run into on the east coast is astounding.
I would say that depending on how rural that commute is and how early you make it I would invest in a car that can handle running some offroad lights for the commute.
Mr. Lee said:A 2.5 altima with a CVT rental we got a few years ago got better mileage @ 84 vs 75 cruise settings. 75 was a consistent 35 mpg vs fresh tank @ 84 was pushing 39. I wanted to attempt a bit faster test but SWMBO was already going on about "not getting a ticket".
The increase in mileage could have been due to the fuel. Some states use 15% alcohol while other states still allow non oxygenated gasoline.
You know what just crossed my mind? It's a real shame the Elio isn't available for purchase...it would be perfect.
I can tell you the c5 in an m6 is at 1800 rpm at 85.
GameboyRMH said:You know what just crossed my mind? It's a real shame the Elio isn't available for purchase...it would be perfect.
I thought the Elio was biased more towards in town driving. I wonder how happy one would be at 90?
I just did a 700 mile trip last weekend averaging 85mph in our 2012 town & country. Mpg for the trip was 25 which I thought was pretty impressive.
Nick Comstock said:GameboyRMH said:You know what just crossed my mind? It's a real shame the Elio isn't available for purchase...it would be perfect.
I thought the Elio was biased more towards in town driving. I wonder how happy one would be at 90?
No, those are meant to shine at highway speeds. It’s mostly aero and aero doesn’t do much at 30. It also has a footprint comparable to a mid size car vs a more in town friendly sub compact. But, you know, vaporware
Has Elio published a CdA?
In reply to Brian :
Hmm I never really looked into them. I just assumed from the few pictures I've seen it would be an anemic tiny little that would struggle to do 60.
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