I have a 95SE 5-speed in excellent mechanical condition, with less than 16k on NGK platinum plugs. I run a Budget y-pipe, a K&N panel filter and 0w30 synthetic oil and typically over inflate my tires by 2 or 3 pounds.

Say I went on a long trip and the time to get there and back was not a consideration, what do you think the speed in 5th gear on average would be to achieve optimum fuel economy, ignoring changes in terrain.

At 50 mph, the tach states just over 2,000 rpms. Obviously one wouldn't want to get a ticket on freeways for driving too slow.

I suspect optimum fuel economy might be around 60 mph, perhaps even less.

I know my fuel economy is certainly worse at 80 mph than it is at 70 mph.

Any guesses out there?

 

In consideration of having a 5 speed, as slow as you can get away with while in 5th would be the best bet. You'll get better economy lugging up a hill and allowing the car to slow a bit than having to downshift. If you see a hill coming up, speed up a bit so that you can afford to slow back down a bit.

I'm also on a forum for fuel economy, and this quote concerning a Sentra might be useful for you.

I get 38 mpg on the highway w/ my 6 spd SE-R at 55 mph. If I push it to 62 mph, my mpg drops to 33-34, and if I push it to 72 mph, my mpg drops to 26. Those are all based on 400 mile drives w/ cruise control.

The thread I linked to from where this quote is taken is talking about a later model Altima, but there are lessons to be learned anyways. The Altima is essentially the same as our older Maximas as far as size and weight, and even use the same 3.5L used in later model Maximas.

I recently did a 1200 mile trip in my 98 with an auto and managed to average 28 mpg, which comes to 450 miles from full to empty (according to the guage.) My car is also stock, but I use 5w20 synthetic, and run around 45-50 psi in my tires (the sidewall calls for 50 psi max). I was afraid to use 0w oil, but I assume you've used it without issues? Only other thing i can think of is I replaced my rear muffler with a used glass pack, but i didn't really see a difference in economy.

On the air filter front, I would be more willing to use a traditional paper filter. The K&N lets through a lot more dust than the paper will, and you won't see an economy difference in our modern engines. If all your sensors are functional you can use the paper filter til it's nearly plugged and there would be no difference in economy. A plugged filter would let in less air, which would make the ECU pump in less fuel to compensate, so there is little difference. I know for me having a K&N made me use the extra power more often(I like fast cars) and I went downhill in economy.

If you can find a longer route away from the interstate where you can maintain 45-50 mph fairly regularly, I'd go for that. I suspect you would enjoy it more, since you seem to be the type that is in less of a hurry. I'd love to go on a long journey for once where I could afford the time to go slowly and take 2-3 breaks a day just to rest.

Check out the ecomodder site for lots of info (more like info overload) concerning fuel economy. You'll enjoy it.

Good Luck

 

The shortest distance between 2 points will give you the most mileage. That being said, a longer road with a slower speed could yield higher numbers per mile, but you are adding miles to the trip. 10 miles at 30 mpg is the same as 20 miles at 60mpg if the destination remains the same in both cases, but it still costs the same in fuel and you waist 10 minutes for nothing but some numbers. Also, roads with lower speed limits also usually have more stopping points and turns. Stops, turns, and hills all decrease mileage. Interstate at 82 over 600 miles got me 27 mpg, including the stop and go city driving while I was at my destination.

 

Thanks shadetree, that was a very comprehensive response.

On a trip I generally set my cruise control at about 6mph over the speed limit. Every summer I drive to my sister's home which is about 250 miles away and my wife goes on to her parent's for a few days which is another 50 miles further. I have gone as much as 540/545 miles on a tank of gas (albeit on fumes when I filled up) on this trip which entails going from sea level to as high as about 6,000 feet on the Coquihalla Highway in British Columbia and down to less than 1,000 feet elevation. It is the same coming home obviously.

So for a good portion of the trip, I am averaging 75 mph and at other times about 68 mph and less.

Obviously if I slowed down and only drove the speed limit I would see an improvement in fuel economy.

 

I'm not necessarily thinking of going the circuitous route.

That's pretty good gas mileage at that speed.

 

My best economy has come from staying closest to 3k as possible without going over.

My theory is this because this is where the engine has to do the least work to maintain speed without eating up gas.

My last trip (77x miles each way) I achieved a high of 35mpg north bound (The whole northbound leg averaged out to be 33.8x mpg). My southbound results were great until I got to Texas when my fuel eco tanked to like 25mpg, making the average around 30mpg (never did the full math on the southbound tank).

But both ways I stayed around 2.9-3k, because it was VERY easy to keep my car moving , more than 1/2 inch of throttle would probably start accelerating the car.

Another person I have fuel eco wars with also has the same results, achieving the best mpg near but not over 3k.

With my previous Maxima (it was stock though), it didn't make a damn difference, I could crusie @ 4k and still get 27mpg, same as cruising @ 2k, as long as I was cruising the mpg wasn't affected.

::EDIT::
BTW, I'm 5speed, don't think I'm crusing @ 3k in an Auto... what is that like 85? lol.

 

I dont know how much truth there is to this but i heard that as for as aero dynamics go, 60 MPH is the optimal point for most cars. Once you go over that, the drag from the air resistance will start to decreas economy... Again, i dont know if there is truth in that or not.

 

*shrug* idk. I've gotten my best fuel economy at 80 in my max (95, 160k, 5spd AUTO, CAI) @ 80 mph I seem to pull about 30 mpg!

 

Not to rain on your parade, but I don't believe you!

 

i try to estimate my mpg going to school and back (chicago to carbondale, IL,, about 300 miles. i seem to get about 29 mpg @ 72 mph.. when the car isnt full of all my school ****

 

Now that is more credible as I have achieved that kind of mileage numerous times averaging that speed for a portion of a trip and less for part of the trip.

What do you mean by estimate your mpg? It isn't rocket science.

I fill to the brim, set trip odometer, drive, fill to the brim again and divide miles reflected on trip odometer (don't forget to reset it again) by the gallons consumed.

Quite a bit of gas can be pumped in after the pump initially clicks off.

 

haha yeah i know its not rocket science. thats exactly what i do except i wait for the pump to click off, i usually dot go any farther than that

 

I also managed to get 30 mpg from a tank where I did 80 mph the whole way. It makes no sense whatsoever. Only thing I can think of is that i didn't stop at all and there was only light traffic, so I didn't have to slow down at all, and the land was flat. I kinda wonder if the car has a sweet spot at 80 mph, which is just uner 3k rpms? I'v been figuring gas mileage since I learned to drive and use the same technique each time. I don't top off much but do give it a few extra squeezes until it starts to argue too much. Completely topping off the tank would add maybe 1 quart so it wouldn't affect the mileage much over an entire tank's worth of driving.

I've been using 89 octane, but am tempted to run 91 again to see how it goes. Last time I used 93 it seemed to be a bit sluggish.

 

@89 octane, stock '97 automatic (my dad's)
Usually averages about 29 mpg on freeway at about 65 - 68mph. That runs the engine a little over 2k rpm.

I get worse with my '97, but then again i do about 80 - 85mph (sitting at a little less then 3k rpm). :P

Theoretically best fuel economy would be when your engine is just a bit over idle in the tallest gear. So, when you are running at about 1.5k rpms in top gear.
Since fuel usage does not increase linearly with engine speed (rather it consumes more then double gas for double the rpms) staying at lowest rpms would be best. That would also assure that you do not go so fast that air resistance starts to come into the equation.

 

Well, lets look at the math

I did 80 fairly consistently driving from Birmingham, Alabama. I got a bit over 500 miles on one tank (i think it was like 504 miles) and drove til I was on "E". Only had to fill twice and had gas left when I got home in Texas.

Do the math. 17 gallon tank/500 = ~30. Roughly 30mpg.

Read it and weep. :]

 

best economy for the engine would be wherever it has the best volumetric efficiency (and not WOT VE which is easy to calculate, but cruising power VE which would be much more difficult), however this does not take in to account aerodynamics and rolling resistance, etc. so it would be the intersection of the curves of those factors, probably with some other factors thrown in that I'm forgetting too.

 

I think this is a time when the theory doesn't match up to reality. If you had asked me the best speed to run the Maxima for fuel economy I would have said the same as the others, slow as possible in top gear, or the speed limit. That's what we did on our trip up to Iowa, we kept it around the speed limit, even allowing the car to slow going up hills a bit. We (my brother and I were both driving alternately) managed to get 28 mpg. On another trip with similar speeds by myself, I managed the same economy.

On the way back, we wanted to get to the house ASAP, so we dropped the hammer and got the cruise to 75-80 mph. We managed 30 mpg (actually 30.45 mpg IIRC) which somehow matched up to everyone else's experience.

The only logical explanation would be explained by looking at the brake specific fuel consumption chart (BSFC). The gist is that at certain rpms the engine's design would create optimum power when compared to the fuel consumption. It is possible the BSFC hits a sweet spot right under 3K rpms.

I've searched to no avail for the BSFC chart for our engine, but in consideration of everyone getting 30 mpg at around 80, there must be something to it.

 

Did you or did you not take the actual miles driven and divide by the gasoline consumed? The tank holds 18.5 gallons.

I have achieved 30 mpg in the past but at less than 80 mph on average, having eked out 540 - 545 miles to a tank about 3 times. However, my car is a 5-speed and that could make a difference on highway mpg.

 

well this is just about as basic as you can get here.

you get your best gas mileage at the rpm where you get maximum torque.

you look at that number, and you can look at your rpms. go slightly over that number, shift drop below then go til you go over shift again.

Simple as can be there. well how your gearing is set up is going to tell you how far PAST your optimum rpm you go before you shift again, just a feel thing normally.
accellerate slowly, hit that spot keep going .... very little gas just enough to get back to that maximum torque ( its going to be more like 2500 but i havent looked it up.)

I had a geo metro that had an idiot light that told you when to shift ( too early)
I believe the light improved gas mileage in the 15 mpg realm seriously. A geo metro is geared really strange and dramatic with a huge 1st gear and the smallest fifth gear you could have without rolling backwards.

It got over 50 mpg for real. beats any car sold today except for the insight in gas mileage, even that little smart car.

 

When i figure my mileage I reset the tripmeter when i refill, and next time i refil i take the miles covered divided by the gallons put back in to refill it.

Lately with my wife running the a/c a lot in her car the car's been getting 22 mpg past couple weeks.

To be quite honest I never knew the capacity of the tank until I had to input the capacity into my Scanguage. I figured it had a 16 gallon tank because I never put more than 15 in when refilling it from empty. Talk about a huge reserve past empty!

 

I am desperate to get that 15 posts on this forum. sorry but thanks

 

On my last road trip, I left here in Jax and when I crossed the border into NC (going up I-95) I had a 1/4 tank of gas left. I was going between 70-75 mph. Once I started getting farther north up into the hills, the fuel economy dropped quite a bit.

One of the benefits of living in a relatively flat area is getting good fuel economy so long as the speed is kept down. If the speed limit is 65, then that's what I usually do, but I go no more than 5 over since you can get a speeding ticket here when you go 6 or over.

 

Bobo is your Maxima still running?

 

Now that I'm more of a troll than I was back when I made my earlier post....


6mt swap.

kthx