# Low revs = better gas mileage?



## Greg200SE-R (Feb 5, 2003)

Is there a general way to drive your car in order to get the best gas mileage? Most people will say to keep your RPMs low as possible, but at some point won't you be making your engine work harder than it has to... 

For example, when riding a bicycle, you'll tire faster if you pedal slower at a higher gear than if you pedal somewhat faster in a lower gear.

I have an SR20, but if applied in general to 4-cylinders, I guess my general question is, in which situation should I be getting better mileage:

-- Cruising at low RPMs (say, 2500) but my exhaust/intake noise is telling me my engine is working a little harder

-- Cruising at a slightly higher RPM in a lower gear (say 3000 to 3250) with my engine purring and exhaust/intake nice and quiet

It's not just the RPMs, but also how far I'm pushing the gas pedal to sustain those RPMs, right?


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## psuLemon (Apr 23, 2003)

i dont know if i really should answer due to the fact, i can't provide any statistical data on my belief, so waht i will say is in opinion and from what i have heard

i believe our fuel cut off is somewhere aroudn redline, but i dont know the exact point where it runs optimal.. from what i have heard, people should shift around 4k and when you are in 5th gear, you should keep around 3k... i have always heard dont exceed 80 as it is a waste of gas which is around the 3k mark.. shifting too low will just add load on your car, so you do need enough power to keep the car in motion.. 



now if someone could provide an air/fuel chart to see where the points of dumping gas occurs, things could be more accurate


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## sukebegigi (Mar 5, 2005)

It's only when you wind your car out past the 6000 mark that you begin to notice better gas mileage.


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## Greg200SE-R (Feb 5, 2003)

sukebegigi said:


> It's only when you wind your car out past the 6000 mark that you begin to notice better gas mileage.


Hmm one more justification for driving the way I do. "Officer, I was just doing my part to reduce consumption of natural resources"

Seriously though, I am interested in hearing you elaborate. Can you explain your reasoning please?


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## Petrovich (May 13, 2005)

Drive at peak torqe point.
There, I said it.


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## psuLemon (Apr 23, 2003)

Petrovich said:


> Drive at peak torqe point.
> There, I said it.


considering all things, i would agree with max tq rather than 6k, cuz you are dumpin excess gas once you pass 5K...


http://www.nissanperformancemag.com/may01/dyno.shtml


lookin at the dyno charts and graphics, peek tq is btw 3750rpm and 4k, which was my previous assumption... but i know when it gets to full hp range, you will be dumping gas... by comparision, get in your car and drive at 6k as compared to 4k and see the difference...


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## Tavel (Aug 21, 2004)

i've notice a trend in my driving

all city driving with an SR20DE: accelerating while...
1. keeping RPM's between 2k and 3k = about 22mpg
2. keeping RPM's between 2.5k and 3.5k-4k = 25mpg
3. keeping RPM's between 4k and 5k =20mpg

so i'd say for city driving do number 2, i've had the best results with 2.5k to 4k range. i always cruise at about 2k-2.5k rpm's, never below 2k and always in the highest gear possible. i cant say highway mileage cus i hardly ever go on the highway


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## chimmike (Oct 17, 2002)

the more gingerly you drive, the better mileage you're going to get, to a point. Revving it to 6k is NOT going to save you any gas, that's for sure.

normal gentle acceleration, do not exceed 4krpm, that should give good mpg on the sr20.


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## thecolonelcm (Mar 28, 2005)

chimmike said:


> the more gingerly you drive, the better mileage you're going to get, to a point. Revving it to 6k is NOT going to save you any gas, that's for sure.
> 
> normal gentle acceleration, do not exceed 4krpm, that should give good mpg on the sr20.


I did a search and found this thread: 
http://www.nissanforums.com/showthread.php?t=79268&highlight=gas+mileage+write
Theres also another one floating around that is really helpful. Cant seem to find it right now though. Somone did a write up on the best ways to conserve fuel: ancicipating traffic, allowing a larger space between the car in front of you... dont date fat chicks... .etc.. If anyone finds it, post !!!


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## IanH (Feb 11, 2003)

Petrovich said:


> Drive at peak torqe point.
> There, I said it.


This was true on older engines before all the electronics and VVT etc. 
And still may be true.
This comes from real data on fuel consumption curve per HP and road mpg vs. speed. These used to be published in FSM and road tests in the UK. 

I changed my Cam on a 1978 Z28 to move the torque peak up to the cruise rpm, and improved the MPG from 14.5 to 15.5 – 16.0 mpg.

Since a major engine loss is pumping losses due to a closed throttle, running harder with lower vacuum but before the mixture is richened for max power should produce the best MPG. For carburetors this used to be about 8 to 10 inches of vacuum.
Also consider that aerodynamic drag increases with square of speed, and reducing speed increase MPG, but we know that don’t we.


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## Flying Vv (Apr 10, 2003)

peak torque point is at 5225 rpms i believe, and is the same peak for every car. after that no more torque can be produced.


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## psuLemon (Apr 23, 2003)

Flying V said:


> peak torque point is at 5225 rpms i believe, and is the same peak for every car. after that no more torque can be produced.


its different for each car.. look at the dyno sheet for the ga and the exel spread sheet


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## bahearn (Jul 15, 2002)

> peak torque point is at 5225 rpms i believe...


5,250 rpm is a constant derived from converting angular force into linear power. Torque * rpm / 5250 = horsepower



> and is the same peak for every car. after that no more torque can be produced.


Powerband is quite variable. My Bandit has peak torque at about 7,500 rpm (Suzuki air/oil-cooled 1200 cc inline four cylinder). Peak torque rpm will be at roughly 60% to 80% of horsepower rpm. Roughly. The Bandit's horsepower peak is at 10,000 rpm.

Any engine that spins past 5,250 rpm will see torque plot cross HP plot at 5,250 rpm. Hardley-Ablesons redline at 5k so their torque plot will never cross. Most diesels don't spin past 3k rpm.


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## muccman (Aug 24, 2003)

I found that if i drive my car sportier (rather then granny shifting it and such) it'll give me roughly 30mpg in the city. Not bad for a 13 year old car.


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## Flying Vv (Apr 10, 2003)

bahearn said:


> 5,250 rpm is a constant derived from converting angular force into linear power. Torque * rpm / 5250 = horsepower
> 
> 
> Powerband is quite variable. My Bandit has peak torque at about 7,500 rpm (Suzuki air/oil-cooled 1200 cc inline four cylinder). Peak torque rpm will be at roughly 60% to 80% of horsepower rpm. Roughly. The Bandit's horsepower peak is at 10,000 rpm.
> ...


 ah yes, my mistake. I forgot thats the corssing point not the peak.


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## IanH (Feb 11, 2003)

bahearn said:


> 5,250 rpm is a constant derived from converting angular force into linear power. Torque * rpm / 5250 = horsepower
> 
> 
> Powerband is quite variable. My Bandit has peak torque at about 7,500 rpm (Suzuki air/oil-cooled 1200 cc inline four cylinder). Peak torque rpm will be at roughly 60% to 80% of horsepower rpm. Roughly. The Bandit's horsepower peak is at 10,000 rpm.
> ...


 
Horsepower is a measure of work done. This is force times distance. 
The 5250 is a function of the definition of the units you are using and is not a fundamental constant. 
So different units, different constant. ie metric 

or change torque from ft lbs to inch pounds in your equation. 

Using your example and going further, hi revving engines do make their peak torque above 5250. For example your motorcycle, I believe the 2.0 S2000 and certainly the F1 racing engines that rev to 19,000 rpm. 

for reference.... 
One horsepower is the work done at the rate of 550 foot-pounds per second and it is equivalent to 745.7 watts. 
This can be angular or linear, it does not matter, its still One HP. Also please note this is a arbitary unit from James watt and steam engines.


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## Petrovich (May 13, 2005)

One thing I know, no matter how I drive my Legacy, it still does 16mpg... Even on the highway. Maybe I should stop hitting the speed limiter, though...


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## sukebegigi (Mar 5, 2005)

chimmike said:


> the more gingerly you drive, the better mileage you're going to get, to a point. Revving it to 6k is NOT going to save you any gas, that's for sure.


Gee whiz, do ya think so?


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## asleepz (Feb 24, 2004)

Get a vaccume gauge... More vaccume you have less gas you use.. (Cruising at a single speed)

And I'm not saying cruise at 45 in 1st gear..


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## IanH (Feb 11, 2003)

Petrovich said:


> One thing I know, no matter how I drive my Legacy, it still does 16mpg... Even on the highway. Maybe I should stop hitting the speed limiter, though...


I assume this is the 2.5 L turbo ?
Auto or 5sp ?
I had a Legacy for 10 years, 2.2 5sp and got 19-21 city and 28 -30 Hiway even when cruising at 80 plus.
So I am not happy I only get 28 -30 from a 1.6 L Sentra on the Hi-way.


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## Will (Jan 2, 2004)

LOL I had to check back see how this Nissan forum suddenly turned into a Legacy forum. I have one of those also. You guys are just 'messin with my head'. Right! Not much of a challenge lol. The best gas mileage of all is don't drive the car. lol


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## Tavel (Aug 21, 2004)

someone forgot to mention that you get better mileage by going faster in a higher gear..to a point. 3k at 60mph is going to get better mileage than 3k at 30mph cus you're going farther with the same amount of work :thumbup:


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## psuLemon (Apr 23, 2003)

^this is true, and one of many reasons why we have 6 speeds now..


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## No_Dice (Jul 4, 2005)

Another thing I've heard (correct me if I'm wrong) is a full throttle opening is the most efficient means of acceleration, meaning put the pedal to the floor for whichever gear you are in.

Also, has anyone tried one of those vortex-generating intake inserts?


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## asleepz (Feb 24, 2004)

No_Dice said:


> Another thing I've heard (correct me if I'm wrong) is a full throttle opening is the most efficient means of acceleration, meaning put the pedal to the floor for whichever gear you are in.



LMAO!!! HELL NO! 

I know from experience


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## Petrovich (May 13, 2005)

IanH said:


> I assume this is the 2.5 L turbo ?
> Auto or 5sp ?
> I had a Legacy for 10 years, 2.2 5sp and got 19-21 city and 28 -30 Hiway even when cruising at 80 plus.
> So I am not happy I only get 28 -30 from a 1.6 L Sentra on the Hi-way.


Tis a 2.5 Turbo 5-speed. It's notthing like subarus of yesteryear... Gobs and gobs of raw horsepower, and I bet if you look hard enough you can see raw gas flowing out of exhaust pipes, too. I hope it's just break-in stuff, otherwise I'd have to start measuring gas mileage in gallons per mile...
As for full throttle thing, I used to drive my Stanza at ~3/4 throttle and shift early to keep myself from accelerating too fast. The thing would then get ~35 MPG on mixed city/highway driving, which, IIRC, is like way better than stock figures. Then, on the other hand, it has all-synthetic fluids and prolly had some "work" done to it by the pevious owner cuz it's mighty fast for a 97hp mid-size sedan 
But then, it's hard to keep your foot off the floor...


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## No_Dice (Jul 4, 2005)

asleepz said:


> LMAO!!! HELL NO!
> 
> I know from experience


I took your advice and ran a test, as I wasn't sure where I'd heard that business: I generally get 38-39 mpg with a wide-open throttle, but for my most recent tank, I was very gentle with the accelerator, and I got only 34-35 mpg, with my normal driving circumstances. So, it my vary from car to car, but a WOT gets me about 3-4 more mpg.


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