Way to get the best MPG out of my car?

[Bubs daddy]

Marlin, I'd have more respect for you if you just admitted you're wrong.

Man up and admit it. You're wrong.

Your car does NOT get better mileage at 55 than 70. It doesn't matter how much distance you cover and how fast you go at 70. It's MILES PER GALLON. It's fuel economy.

You get better miles per gallon going 55 mph than 70 mph. It's a fact.

It doesn't matter what you or your buddies or your computer says. IT'S WRONG.

I don't know of any consumer gasoline powered vehicle that gets better mileage going 70 mph than 55 mph. It's been known for years.

It doesn't matter what your dad's company does for Nissan. It doesn't matter that you're close to being ASE certified. You are wrong.

So stop spreading misinformation. Look at the research. Look at the studies. Look at whats been out there for decades that everyone knows is common knowledge.
Modified by Bubs daddy at 9:22 PM 10/24/2008

[Bubs daddy]

Quote »Wow. Going slower doesn't automatically mean better mileage. Each car has a cruising RPM where it's most efficient. My CVT gets better going faster than it does slower because the CVT has too low of an RPM at 55 or below and it lugs it down a little but once I go faster, it starts to get into the range where torque increases and carries the car more easily.[/quote]No one is talking about lugging the car. We're talking about two cars traveling at the same elevation in the same conditions. Marlin is talking about his freeway commute and the other poster asked in general how he could gain more mileage.

Your Nissan Versa with CVT gets better mileage at 55 than 70. It's a fact.

[Bubs daddy]

Quote »And I believe marlin29311 is talking about time/fuel use. I can see what he is saying about the distance cover vs speed vs gas consumption.

[/quote]No, what we have here is backpeddling and posting misinformation and someone not man enough to admit it.

And it's simple what we're talking about. Fuel consumption. Miles per gallon.

It has been documented for decades. Driving at slower speeds saves gas. If you go on the freeway and drive at a constant speed, you will get better mileage (miles per gallon) going 55 than 65 or 70.

People are trying to make something complicated that is not complicated.

[marleyfan]

I get it from the computer readout built into the altima based on the same 40 mile patch of I-95 between NJ and philly. I go to philly a lot (graduated from school there) and I tested this out. No A/C either times, windows closed, fair temperatures, minimal traffic, if any. Almost constant speed (impossible to keep a constant speed with hills and such). I'd take pictures of the computer, but I don't take pictures while driving.

Try each speed numerous times through the same section going in the same direction and be sure to use cruise control to eliminate pedal feathering. Then see if your results are the same. To be honest I suspect you've looked at your mpg through this section at those speeds once each and based it on that. If I'm wrong I'm wrong. I trust that you believe what you are saying but I don't trust your methodology.

[Shad0wXCalibur]

No one is talking about lugging the car. We're talking about two cars traveling at the same elevation in the same conditions. Marlin is talking about his freeway commute and the other poster asked in general how he could gain more mileage.

Your Nissan Versa with CVT gets better mileage at 55 than 70. It's a fact.

Then why do I get a little better mileage going 65 mph on the interstates than 55 on some of the highways here?

[Bubs daddy]

You're not. Your calculations are off, or as Marley mentioned your methodology is incorrect.

Doing A-B comparison and testing requires identical or near identical conditions.

The fact is, your car is working more to keep it at 65 than 55. It's using more air and more fuel.

[grogman]

did you know that when fred and barney commuted in the morning they had a hybrid vehicle.........and that my friends is a geico moment.......

[KimberKenobi]

the Camel got it's best tank (42 mpg - only ever hit 44 in Camel #1) while driving the highway in Montana at 90...

I find that sometimes 60 yields me great gas mileage (38) but that if I can hit traffic just right and stay steady I get 36-38 at 80 too.

In Louisville we have RFG... it sucks for mpg. So I try to fill outside of Louisville whenever possible.

However, with you having the 6 speed, staying as close to 2800-3000 rpms is probably your best bet.

[Kolk1]

Im with Marlin.

Basically a slide scale has to be used. Not Lower = Better. There will be a point (NOT 55) when the faster you go, you get worse gas mileage. ALOT of variables come into play, mainly being Drag.

If you increase speed by 15%, but gas consumption only increases 10%, your getting better gas mileage, but if you past that and increase speed by another 15%, but now you have crossed your drag fresh hold, and gas consumption went up 20%, you are now getting worse gas mileage.

55mph is not the end all answer. SLOWER is not the end all answer. You have to find the point where your % of throttle and drag, are overcome by the % of fuel.

Some cars maybe 45mph, some maybe 70. I know my C5 corvette seems to do its best at 75, but ive made alot of changes to that car.

[KimberKenobi]

...

I'm sorry, were there words in your post?

just teasing.

[Kolk1]

Let me know if you want any pics.

List of cars since I got out of the Marine Corps.

07 Nissan Versa05 Yamaha Raven R107 Yamaha Glare White R606 GoMango Daytona ChargerC5 Corvette, 527whp 544wtorque02 Camaro, 11.1@122Z32 300ZX, NA + bolt ons and nitrous 13.8@10391 Civic Si, Engine Swap B16, and Turboed92 Honda Accord, Stereo stuff. 94 Del Sol, B18 Engine Swap79 Datsun 280zx, stock82 Camaro, stock just repainted it.88 Caprice Classic, stock, no pics94 Ford Probe, full stereo, body kit, FSZE swap and nitrous

Some I left stock, some I modded then traded for other modded cars. Blah.

Out of all the cars ive owned, I miss the C5 and the 300zx the most. I plan on buying a C5 Z06 right after I get settled into my new house. My C5 I used to have was an Auto, and I set it up for drag racing. When I get a Z06, It will of course be a manual, and just be a all around fun car, with basic mods, Intake, Full exhaust, small cam, better clutch, and that should be all.

[KimberKenobi]

Z32 300ZX, NA + bolt ons and nitrous 13.8@10391 Civic Si, Engine Swap B16, and Turboed94 Del Sol, B18 Engine Swap79 Datsun 280zx, stock

... ...

94 Ford Probe, full stereo, body kit, FSZE swap and nitrous

I applaud your tastes... but the 90 body style was WAY better... I had one. XoD

[Kolk1]

... ...

I applaud your tastes... but the 90 body style was WAY better... I had one. XoD

Well, when I bought the 94 Probe, I really wasnt into cars, just stereos. While owning that car, I got into performance, thus came the motor swap and nitrous, then said F it, and bought a new car. lol

[DUCeditor]

I'm not going to join in the wrangling. But I will make this observation: My 2009 Versa SL with CVT is more fuel mileage sensitive to small changes in driving style than any other car I have owned.

My daily commute is 150+ miles. About 50% is on multi-lane highway, 35% in fairly open two-lane roads, and 15% in a semi-urban enviorment.

If I drive at 50-55 on the two-lane portion and 62 on the highway (speed control set) I'll get 37 - 40 mpg depending on how busy the "urban" section is. - i.e, how many lights I get stopped at. But any change from that lowers my mileage to the low 30s. Such changes include accelerating quickly away from lights in the urban section, increasing my highway cruise speed to 70+ or just giving it enough gas so that it "downshifts" - i.e., the rpm rises - on hills.

So... moderate (but not crawling) speeds on highways and gentle everywhere else. That's the ticket for high MPG.

-don

[Kolk1]

I asked my buddy about this topic. For reference, when he talks about his car, he has a highly modded C6 Z06, and hes an engineer for Diamond Chrysler. This is what he had to say when I asked him.........

55mph for peak fuel economy is a myth.

Now... that said... it's definitely the general area for peak fuel economy in a vehicle.

Drag vs. engine power vs. fuel consumption is what needs to be looked at.

You brought up a Corvette, so I'll talk about mine. My Corvette actually geats peak fuel economy at 75mph. The gearing and power capability of the engine is the reasoning behind this (plus the cam dramatically shifting the power curve). When it was stock, peak fuel economy was around 65mph. I checked this through both the onboard fuel economy reading (which is based on injector pulse width, engine speed, and vehicle speed) and through actually dividing mileage traveled by fuel consumed. The Corvette is a lightweight vehicle with a low coefficient of drag, and the obnoxiously wide gearing allows the engine to operate at a high brake mean effective pressure at a low rpm. This means the engine is running more efficienctly at a lower fuel consumption rate.

Now, compare that with a typical economy car. Most cars are calibrated (both via the software and actual hardware, like the transmission and engine setup) for 58mph peak fuel economy. That's not an exact speed, but it's pretty close, because most vehicles generally share similar traits when comparing the powertrain's capability of delivering power versus the vehicle's drag (both from the wing, tires, and any outside factor).

If you have a given vehicle with a given powertrain, you can find the speed at which it would be most efficient. To do this, you'd need an engine dyno with capability to measure fuel flow. The idea is to find the minimum brake specific fuel consumption, or BSFC. BSFC is simply the fuel flow rate divided by the power output. This is typically most efficient at WOT and peak torque. Basically, starting at idle and locking in the rpm, you'd sweep the load range, measure power at every load (let's say every 5 MPa of manifold pressure), and then increase rpm by 200. Repeat this until redline so that you end up with a chart that has an axis for rpm, an axis for manifold pressure, and cells filled with BSFC.

So now, let's say you've got an engine that makes peak torque at 4000rpm. Chances are, the best BSFC is at 4000rpm wide open throttle (engines are most efficient when not throttled). So, at probably 100 MPa and 4000rpm, this engine is at it's highest efficiency. Let's say this is some little 2.0L 4-banger. For argument's sake, we'll say that it's making 100hp (TO THE TIRES) at full throttle at 4000rpm. The vehicle that this engine is in takes only 80hp to overcome drag at 55mph. At 65mph, the vehicle requires 100hp to overcome drag. Overcoming drag means the vehicle's energy production is enough to maintain vehicle speed at a given speed (effectively cancelling drag). Since 65mph requires 100hp to maintain, and the engine can put 100hp down to the tires at 4000rpm at full throttle, you'd want a transmission that makes the CRUISING gear run the engine at 4000rpm with the vehicle at 65mph.

Now let's use my LS7 for example. Mine makes peak torque at about 5000rpm, so it's safe to assume the best BSFC is at that rpm. However, my engine makes about 500whp at that rpm. Let's say my vehicle needs only 75hp to maintain 55mph. Theoretically, the engine operating at the best BSFC would net a vehicle speed in the 140s. This is a gross over-simplification, though, so these numbers are for example only. Theoretically, if my engine is operating most efficient at 5000rpm and makes 500rwhp, and it takes 500rwhp to maintain speed at 145, then it'd be best if I could get a gear that did that. These numbers aren't true though, because 4th gear would match that fairly close for me, and at WOT in 4th, the car accelerates past this mark. If you're at WOT, peak torque/efficiency, and a "cruising" speed, then you're topped out.

I'm sure you've all figured out the major problems with this, though. First off, some vehicles would be traveling at obnoxious speeds for peak efficiency. Second, this doens't even begin to incorporate emissions, which would be huge. Third, if you're basically at WOT in your driving gear, you'd have no passing power. This leads to the last point... if you have to take the engine to redline just to accelerate to cruising speed, and then run this thing at a high rpm on full load for a long period, that's going to cause some serious durability problems.

Ultimately, vehicle manufacturers balance out engine economy with emissions, longevity of parts, and drivability. They want you to still have some passing power, they don't want to pay for repairs, and they have to meet emissions restrictions. Ultimately, though... don't think that just because your engine is turning a low rpm that you're getting better fuel economy. Efficiency does not linearly scale with engine load or engine rpm. Because of how manufactuers set up vehicles, most of them are going to do their best around 60mph. There will ALWAYS be exceptions, though. It is not concretely set at 55mph for every vehicle, that's a fact.

[marlin29311]

Marlin, I'd have more respect for you if you just admitted you're wrong.

I'm not looking for your respect - i'm looking for you to open your eyes and stop believing the "experts" and do some testing on your own. Do you believe everything people tell you? I sure hope not. Try doing some real testing on your own with multiple vehicles and then come back and tell me that every car you tested from every class of car got it's best fuel efficency at 55mph. I'm telling you that based on my personal testing under controlled condition (as controlled as someone who doesn't own a personal track to test on) has yielded my car getting it's best MPG's at around 70 mph. You can tell me that you think I'm wrong all you want, but that's just being ignorant. Try doing your own testing.

Try each speed numerous times through the same section going in the same direction and be sure to use cruise control to eliminate pedal feathering. Then see if your results are the same. To be honest I suspect you've looked at your mpg through this section at those speeds once each and based it on that. If I'm wrong I'm wrong. I trust that you believe what you are saying but I don't trust your methodology.

I can understand you're skepticism, but I've done this multiple times on multiple days (as i said, i got to Philly a lot and drive this strech of 95 a lot, and I try this out almost each time I go), under the most control that I can have under the circumstances. I don't use cruise control as it seems to over-rev on certian hills along the way - i keep my speed within 2-3 mph of the target speed. Every time I do the trip, I get just about the same mpg reading ( + - .5 mpg).

I asked my buddy about this topic. For reference, when he talks about his car, he has a highly modded C6 Z06, and hes an engineer for Diamond Chrysler. This is what he had to say when I asked him.........

55mph for peak fuel economy is a myth.

Now... that said... it's definitely the general area for peak fuel economy in a vehicle.

Drag vs. engine power vs. fuel consumption is what needs to be looked at.

....rest of long quote

Thank you! Someone that does their own research and doesn't believe the "experts."

[Kolk1]

Thank you! Someone that does their own research and doesn't believe the "experts."

Im not going to argue about this, but I thought Id share my "opinion", My buddy Dave is more of an actual expert, and thats why I asked him. I was waiting for him to shed more info on the subject.

Like I said, if hes looking for somebody to argue with, its not me, but I thought id add some other insight on the subject.

[marlin29311]

I was referring to the people at the EPA and the like, who do all of their "testing." I agree more with the people who do independent testing like your bud, who understand cars much deeper than the average person.

[Kolk1]

Yea, I see what your saying. But looking at it from the EPAs stand point, they have to have a standard test for all cars. They cant do tank after tank of gas on each car to see what speed it gets its best gas mileage. So they probably test all vehicles at 55mph and leave it at that. If its gets better at a higher or lower speed, thats for the consumer to find out.

[Samyo]

...which is in essence saying that every car does it's best at 55. Does the car get better gas mileage at 45? Then 35?? Hell, I should just stop driving because that's my best gas mileage!

There is no way of proving every car gets better gas mileage at 55 over 65 without data. Going from 55 to 65 is a 18% increase in speed - can you prove that every car has an increase of fuel consuption of over 18%? How long of a drive are you talking about? The longer you are at a steady speed, the better you can realize economies of scale on your engine (aka efficency). There are way to many factors to make a blanket statement saying every car gets better gas mileage at 55 over 65.

I have an '08 altima coupe 3.5 and I get better gas mileage going 70 over 55. This is based on a steady 50 mile trip. Woops...there goes your theory. Each car has it's own speed that it reaches peak efficency. Stop believing the garbage the EPA trys to feed you.

Cars get more miles per gallon with lower RPMs. Period. Less stops, less starts, and low RPMs will produce better MPG than otherwise. If we took two identical cars, and started them at point A, one accelerated to 55, and one accelerated to 65, if we then drove 50 miles, the car going 55 will use the least amount of fuel. This is a rudimentary idea. The four-stroke engine uses fuel on every stroke. More strokes, more fuel.

[marlin29311]

Cars get more miles per gallon with lower RPMs. Period. Less stops, less starts, and low RPMs will produce better MPG than otherwise. If we took two identical cars, and started them at point A, one accelerated to 55, and one accelerated to 65, if we then drove 50 miles, the car going 55 will use the least amount of fuel. This is a rudimentary idea. The four-stroke engine uses fuel on every stroke. More strokes, more fuel.

Wrong. So you're telling me that since a car has lower RPM's at 35 that I am going to get better gas mileage at 35 than I am at 55, where I'm using more rpm's? I think not. Peak efficency is not the same on every engine in every vehicle because of engine architecture, transmission layout, etc. Bub's has a more convincing arguement that this one, and I still don't believe his.