Nah, I don't think the logic would work. But interestingly, I was reading about a Sea Ray that was capable of 52 mph (knots). They actually tested and reviewed, and spit out the fuel consumption at various speeds. The sweet spot or maximum mpg occured at 37 mph--at that speed the mpg's were higher than any speed lower or higher. It was a whopping 2.8 mpg!!!

If those calculations were applied to a Maxima whose top speed is 137, then 97 would achieve maximum fuel economy. but of course that defies common sense, just like a 15W50 Mobil 1 making your motor make strange noises until you drain it. From experience my Max has delivered the highest mpg's at around 73 mph--it's done 30+ mpg on a good day at that speed with the cruise control.

 

UMM ok.

 

always thought 50mph you get the bast gas mpg

 

i heard it was 55...thats why FDR [i think] put up speed limits of 55mph during the depression to cut back on ppl speeding and supposedly that worked...but hey, those were the the 30s [i think] and things change
atw

 

Probably a physics major could help out on this one. I think you probably use less fuel at 50 mph than 73 mph, BUT the marginal amount of fuel at that higher speed gets you 23 miles further per hour, and the MPG is actually higher.

When the car was new I used to have to make this 440 mile round trip with it, 1 or more times a month. It could knock-out 31-33 mpg consistently when I put the cruise at 72-73. I've never come close since but the car only gets a chance to go on the highway at a steady speed for about 55-60 miles tops these days, which isn't really long enough to get a good mpg calculation.

 

Ditto

 

72-73 does seem like the sweet spot. I drive 160 miles per day and my max get 32-33 mpg if I cruise around 72.

 

Please correct me if I'm wrong, but i don't think the 55 mph speed limit came in until the early 70's...

 

Good to hear you get that mileage. I used to be able to, but I just don't have any highway trips that exceed 60 miles to be able to check on it. When we don't go to the shore I don't even drive 60 highway miles!

That was always the shocker on the VQ--4 cyl. Camry mpg's possible, with 190 hp and 205 ft-lbs!

 

Optimal fuel mileage usually occurs near the torque peak rpm of the motor. Peak torque rpm is where the engine is most efficient. On the Maxima, that's around 4000-4500 rpm. One thing that also needs to be accounted for is drag resistance at high speeds, which increases exponentially as speeds increase. I can't account for that, but drag typically does not become significant until close to 100 mph.

However, the best mpg I've achieved was when cruising with the cruise set to 90 mph. I was able to get 32 mpg in Colorado, and 29 in Texas. That 90 mph corresponds to ~4500 rpm, which matches the peak torque rpm guestimate reasonably well.

The old "50 mph is optimal for fuel efficiency" rule-of-thumb came about in the 70's during the oil crisis. Back then, huge displacement engines that were realllllly detuned were used. We're talking 400+ cu in motors that only made 150 HP. This meant those motors had peak torque right off idle, like 1000-1500 rpm. With the reallly conservative gearing used back in those days, this meant 1000-1500 rpm occured in top gear at 50 mph, and the cars therefore achieved peak efficiency/mileage at around 50 mph. These brick-like land barges also were not at all aerodynamic, so drag resistance became a significant factor at lower speeds like 60 mph.

 

Why do people always say that in order to get good fuel economy, keep the tach below 3K?

 

If that's true, and it sounds very plausible, then that's VERY interesting, Keven. Like many, I assumed that 45-55mph was the sweet spot where the sum of friction and drag was lowest. It would make sense with newer, smaller, more powerful engines and aerodynamic cars that optimal fuel mileage would occur at a higher speed.

So is cruising at peak torque rpm ,e.g. 4500 rpm, for long periods of time on the highway ok for the engine? At first, it would seem that running at higher rpms puts more wear on the engine, but obviously the engine doesn't have to pull as hard when it's doing 4500 rpm at a given speed versus when it's doing 2000rpm at the same speed.

 

If you accelerate to redline in each gear, you're obviously not going to get as good economy as if you shift at 3k. If you're going past 3k in each gear, chances are that you're accelerating pretty fast and burning a lot of gas. If you are just cruising at 4500 rpm that's another story.

 

whoops...then im guessn it was the other roosevelt...mah bad...or maybe i have NO idea what im talkn about
atw

 

Doesn't mpg depend on the gear ratios...That is why the vette gets great mpg because it has an extra overdrive gear (the sixth). I think a combination of drag and gearing will depend on what mpg is optimal for a certain car.

 

Should have nevr told me that. I will do anything to save money. 97 in residential comunities.

 

Hey Frank;

FWIW, 52knots = 59.8mph

1 nautical mile (knot) = 1.15 statute mile (roads)

 

It happened when I was a kid in the mid 70's. There was a gas shortage and you could only buy like 3 gallons at a time(or something crazy like that). The 55 speed limit was imposed to reduce gas guzzling.

 

Works for me.

I have been driving extremely conservatively for the last couple of weeks. I never get above 2k RPM except on the highway where I cruise at 65mpn...approx 2300 RPM.

My average MPG has jumped from 19 to 25.

 

ok 30 mpg seems really high. I have never been able to get over 25/26. I need to know what you guys are doing to get that type of mileage. I drive 70-75 most of the time when on the freeway. Do you guys have mods? Do you guys drive a 4th gen? My car has about 40k miles so my plugs and throttle body and all that good stuff should still be good. Air filter is clean. Give me some advice guys. Have any of you guys tried that warpspeed b-pipe fix? THey say an extra 2-3mpg.

 

Because its true. I notice once I get the car over 3000rpm's, my mileage goes to hell.

 

Dont drive 70-75, drive at 50-60mph.

 

I agree with you. I always travel about 300 miles every weekend and I always cruise at 73-74mph at I-94 between Milwaukee-Madison, WI.

Mpg is dead on at 30+, assuming you never stop. Once you stop/reaccelerate though....it would be around 29...and if you keep on decelerating/accelerating along the way (due to traffic), it would be around 27-28.

City? This one is usually around 22-25 for me...