Efficient car for higher speed cruising
 

What type of car would be efficient for high speed cruising, say 100mph, 160 km/h.

I know this is not entirely in the spirits of ecomodding/driving but sometimes it is just more economical to go fast. For example if you are many people in the car. Or in my case, if I can go fast and avoid rush hour traffic I can see a significant gain in mpg. Getting stuck in traffic sucks. And mpg goes up. (I once got 43l/100km. Going up hill for 2 hours at 3km/h) I could have walked that distance significantly faster. (I have started to bike to one of my workplaces 20-km one way 40 km round trip)
Sometimes blasting on the highway to go through a densely populated area at traffic free is an fe plus.

So, what would be a good candidate? A vw polo or a Passat variant have the same cdA of 0.66 so in this respect would they both get the same FE?

Aero mods would provide a significant advantage, also a gear swap if possible would make the most obvious advantages in my opinion.

Perhaps a motorcycle.

The Prius has a very low Cd and a variable gear ratio, so that would be my candidate in a car. If 2 seats were acceptable, the first gen Insight.

Generally any car that gets good efficiency at lower speeds will tend to outperform other cars at higher speeds.

No sense in making a purchasing decision based on this though unless driving 100 MPH is regularly done, in which case, I would buy something with a high safety rating.

I do ride a motorbike aswell. I have 3 of them. Unfortunately its not that easy to fit 3 people on one.

If I had such a luxury I would acquire a Volvo V70. Very safe, powerful, large, and fairly economical.it's a really nice car and I'll probably buy one one day. (Its on my car bucket list)
Around here a perfect condition V70 can be had for $5k-$8k.

I think a C class Benz with the 2.2 diesel would be the best, they even make a hybrid version. .24 Cd, not huge, don't know what the cdA is but must be pretty good with that .24 Cd.

You’ll subject the vehicle to a wear-rate not offset by putative fuel savings.

While it would not be ideal for the car to cruise at 100+mph (my Saturn gives me around 19mpg at that speed here in WV), you’d be best off with a diesel car(WV/Audi) that’s been streamlined as best as you can manage

Mercedes tends to have very low drag ratings on their cars. I'd probably avoid VW/Audi over reliability concerns. Given the choice, I'd pick a diesel over a gasser.

Other than that, look at Toyota's and Honda's hybrids, they have lower drag and this would slip through the air more easily.

I wonder if a streamlined C7 Corvette would do well enough cruising at 100? It might look weird with smooth wheel covers and grille blocking but I could imagine maybe 25mpg

I read somewhere that the 7th gen Civic gets 18 mpg with cruise control set at 110 mph. And that's with the stock drag coefficient. Not sure if it was manual vs. automatic or coupe vs. sedan.

100 mph is not particularly common here, but speeds in the 90's are (rural freeway speed limit is 80). I think many drivers feel that crossing the three-digit threshold will incur greater wrath from the State. Not a bad assumption.

The Nissan Altima with a 4-cylinder and CVT gets in the upper 30's to low 40's at freeway speeds here (altitude around 4 to 5 thousand feet; usually very dry air, especially on rural freeway). The Camry is a little less efficient at speed (drove a rented Camry from SLC to Las Vegas and back. It averaged about 38 mpg at 80 to 85 mph most of the way.

Engine and drivetrain efficiency are big factors these days. 6 and 8 speed auto-shifters or CVTs can make former gas hogs sip fuel. The Subarus are a good example of that.

I have seen Prii going very fast on the freeway. I raced one, unintentionally, from Auburn to Reno on I-80 and the Prius was doing 85 comfortably up the grade. I was driving a rented Hyundai Elantra (a pig in crosswinds or headwinds with a drop in mpg to low 20's or even high teens). (A heads up to cross country travelers. Driving a rental car at the posted speed limit (I always slow down for cities and towns) while reclined, wearing shades and sporting a full beard will get you facially profiled in Nevada. I didn't get a ticket, but I had a very long chit-chat with the nice officer before he let me go.)

Cars that have a good Cd do not necessarily perform well cross-country or at high speeds. Cross-winds and head winds, as well as shifting and gusty winds are often not replicated in wind-tunnels, especially for cars (and when the Cd is to be used as a marketing tool), so what performs well in the lab does not always do well in the real world.

THE Altima I had got about 30-32 on the freeway here in WV, going 80mph... it was the QR25DE/CVT model and at that speed it turned like 2400 RPM...

Thin air does make a difference, and long flat, straight stretches. Not much of that in WV, iirc (I had in-laws in Nitro). I can get around 30 mpg in my T&C doing 80 mph here, unless there is a strong headwind or crosswind, which is fairly common. A good tailwind pushes it into the low 30's, but the return trip more than cancels it out. Not rushing up grades, of which we have many long and steep ones, keeps the overall trip efficiency up.

A big car with a big engine can get pretty good gas mileage. I drove an old Impala (Sixth generation) to the Bay Area and back in the '80's. It wanted to go 80 and got significantly better gas mileage at that speed (I think around 18 mpg, to the chagrin of my cousin who insisted on driving his turn at the posted 55 mph and got crappy(er) mpg). I drove a Pontiac station wagon of similar vintage and model (with the towing package) back from the Bay Area and it cruised quite comfortably at 90 to 100 mph -- until I got a ticket 20 miles outside Austin, Nevada. The patrolman was somewhat apologetic, but said it was a safety issue, as there were free range cattle in the next valley. He was correct. I could see them from ten miles away.

Again, thin air makes a big difference and most of my driving has been at 4,000-5,000 feet in semi-arid to arid environments (daytime humidity levels commonly below 10 percent outside the Wasatch Front).

It’s the hills that kill my highway(freeway) mileage... my Saturn averages about 36mpg on the freeway, running 75-80mph but for the brief moments the road becomes flat, my instant MPG swings up into the forties

I am curious if an audi a5 or Tt or a posche would yield better FE in this application.

Id personally go with a diesel A5, given those three choices...

I was wondering if that type of car woult trump a 1.2 tdi VW polo.

My understanding is that diesels (especially the bigger ones) dominate the Autobahn. They might not be quite the fastest, but if you have to use it a lot it becomes a lot cheaper with a big diesel.

In the US, GM LSn V-8s have been great at this, although other cars now seem to have the huge overdrives as well.

Good aero is key. Aero losses will double over 70mph. Unfortunately while coefficient of drag is typically published, frontal area is not. Car companies would rather sell a CUV or SUV, while you are obviously looking for a car.

To find a car that will operate in the BSHP "island" try to find a car that has an unlimited maximum speed of ~150mph. BSHP tends to operate at 30%-50% engine load, and 100mph should be ~40% of the load needed for 150. Unfortunately most cars that can do this have limiters here or lower. [Any guesses? I remember 80s muscle cars having top speeds in the 140s and hp between 200-240, but hopefully aero has gotten better. And don't count on those hp/speed numbers being quite the same era].

Ideally you should have a gear that is at near peak torque at 100mph, or slightly lower. That should be right about the center of the BSFC island, but you don't want to be so high in revs that you wear out your engine.

CVTs aren't quite as impressive as we might hope. Que Jason Fenske:
https://www.youtube.com/watch?v=HanImTejIVM
Of course, this implies that Toyota CVTs with said gearing shouldn't have trouble at tall gearings. Still, look for tall gears that put you in the BSFC island at 100mph.

Good luck!

My understanding is that the island of efficiency is more like ~75% rather than 30-50%.


https://res.cloudinary.com/engtips/i...sfcom617a2.jpg

Specific models are one way to make recommendations. Another way is to suggest design characteristics to seek out. Seek taller gearing and lower drag coefficients. I think you want a car with drag below 0.30 & preferably as low as the Prius. And you would want the tallest gearing you might get, as found in the Chevy Cruze Eco in the USA or any CVT equipped car stateside or in Europe. Basically, keep RPMs & drag down as much as is practical.

This will get you to work in a hurry...

https://s3.racingjunk.com/ui/3/03/48...TER-COMPLE.jpg

Sadly, I live more than 1/4 mile from work...

Yeah, usually around 75% of peak torque, but about 35% of peak power. You'd want an aero car that at 100 MPH is producing 35% of peak power. I base that off of the BSFC chart I studied to understand how they work:

http://ecomodder.com/wiki/images/e/e...FC_cleaned.png

This assumes most of the driving done is at this speed. No sense optimizing the car to that speed if it's only occasional.

Really though, I'd probably get a used EV as a commuter and a nice ICE for longer trips. EVs are efficient at most any speed, and excel when stuck in traffic.

This is way too complicated! I will just keep under 100 KPH!

There are online calculators where you can enter the vehicle Cd and frontal area, and it will calculate HP required for a given speed. Find a car with an efficient aero shape, and then plug the numbers in to find the required HP. The amount of power needed at the target speed should be 35% of max horsepower, and the gearing should be such that the horsepower is achieved at 75% of peak torque.

Yes, fairly complicated.

EVs operate between 85-95% efficiency throughout the range, so they are good for just about any speed or operating condition.

That's ok, how long does it take to coast down from 300mph?

That is good. Otherwise you would pass at 300 MPH.

I think I can coast a mile from 60 MPH. Two miles from 120 and three miles from 240?

I'd start with a Prius, and boat tail it. I've only had mine up to 85, but it was surprisingly smooth at that speed.
Here's a video of a 2007 at 108 MPH https://www.youtube.com/watch?v=mzFK56epaHI
and here's a prius at 195 KPH https://www.youtube.com/watch?v=Erzh7Qzq4bk

I find my Prius (and most cars) over-report speed by about 3%. Still, the fine for doing 105 MPH in a construction zone wouldn't be pretty.

The Prius is an excellent choice given the great aero, and variable gear ratio which will keep the car in the most efficient RPM and load range for the given power demand.

"Sir, do you know how fast you were going?"
"This is a Prius! She can barely do seventy-five!"

LAPD reported Rodney King's Hyundai going so fast, Hyundai had to point out that his car wasn't capable of those speeds.

I'd rather be drafting in traffic. Being the slowest looking car in the line makes them overlook you in the first place, rather than make you explain that your car is slower than the cop says it was going.

Lots of smaller engined cars will need to enrich the fuel mixture to keep the engine components cool at high speed. Something like the Prius may not, if it can get enough power from the electric side of things.

A car with a larger engine may be a better choice. Maybe even really big. A C6 Corvette has a CdA of .55 m^2. They can easily get 30 MPG on the highway. It'd probably do pretty good at 100 MPH too.

Find yourself one of these ;) :

http://ecomodder.com/forum/member-fr...ve12d2-549.jpg

I've got a stroker 1776 on the bench (the famous Mileage Motor) that would push this to 50mpg at some speed >60mph. It would do 90 mph with 25hp.

Since I haven't scored one of the two in existence (:() I've settled on this:

http://ecomodder.com/forum/member-fr...7-100-1157.jpg

The Audi/Passat/Dasher body in the three-door bodystyle, with a longitudinal diesel and a five-speed. If the money were to show up unexpectedly, I'd make it a mild hybrid with a Buick altermotor. Then add the turbo.

I wonder how well a person would fare by swapping a Duramax diesel into a base model C7 Corvette... it has the gearing to get 29 highway(rated) with the LT1... would have torque comparable to the new ZR1, with expected highway mileage of at least 32-35mpg, maybe more if the engine were “emissions deleted” and the car itself aeromodded...

EDIT: I just seen the latest version of the Duramax V8 is rated at 445hp and 910lb/ft (2800 and 1600 RPM respectively)... imagine mashing the throttle at highway speed, in 7th gear, and be met with that much torque!

The funny thing is, the people that swap these into other cars seem to claim that the Duramax doesn’t seem to weigh much more than the LSx engines native to the Camaro and Corvette... I don’t think handling would be negatively affected much

Depends on the generation of LT1, but more recent ones with cylinder deactivation probably get very close to diesel fuel economy, with the major difference being the energy difference in the fuel (and price per gallon).

EDIT: I'm willing to bet running the engine on the lean side under low-load cruise conditions would be a better use of time and energy. Let the gasser act like a diesel under some conditions by varying AFR.

I was referring to the 6.2L variant in the C7... I’m not at all against lean burn at low load... just was figuring that the diesel would be better at high speed due to all the extra torque

Diesel VWs have awfully long gearing, and should be doing just 3k rpm at 100 mph.

Find the best CdA that you can. If you can modify the vehicle, pay close attention to the road-load at 100 mph and optimize the final drive in top gear to coincide with a high efficiency region of the BSFC map. You could do this on a BSFC map (assuming you can find a published map for your engine) by estimating road-load power and fitting lines of constant power across a BSFC map. Look for minimum BSFC at the 100 mph road-load power and select your gearing.

Of course, that would cause the NOx emissions to go through the roof since the 3-way catalyst cannot reduce NOx when lean of stoichiometry.:(