Best MPG

[SleepyGorillaMuseum]

Was wondering at what RPMs does the 2.5 create the most torque?

[rockfordrabbit]

Probably should change the title of the thread.


For the 2010 peak torque is at 4250 rpm (I believe its the same for the 08s and 09s too).

I belive the 150HP versions had peak torque at around 3750 rpm.

[argue53]

im confused w the title and the question.

[le0n]

well, if you know where the torque is at it's highest point. you can stay away from that area in the band. more torque, equates to more fuel...

for instance, i cruise at 60mph in 5th, on the beginning of the flat-plateau trend of the torque line (2500-3200k) around 140 wtq. In theory, our best highway cruising speeds will be on the plateau. After that, the gas requirements jump to give you the spike in the power band.

here is a chart i made for the 08-09 (left-hand axis is wtq, whp & mph)

[rockfordrabbit]

well, if you know where the torque is at it's highest point. you can stay away from that area in the band. more torque, equates to more fuel...

for instance, i cruise at 60mph in 5th, on the beginning of the flat-plateau trend of the torque line (2500-3200k) around 140 wtq. In theory, our best highway cruising speeds will be on the plateau. After that, the gas requirements jump to give you the spike in the power band.

here is a chart i made for the 08-09 (left-hand axis is wtq, whp & mph)

Someone has been misleading you....... the specific torque output of the engine at any particular rpm has very little to do with fuel economy directly.
The gearing of the transmission, the engine speed (and associated fuel metering) and the drag created by the cars forward speed are what determine the perfect crusing speed for fuel economy...not the torque curve.

And it is totally incorrect that "more torque equals more fuel"...just plain wrong.

Edit: Think about it, If what you are saying was true...then the poor GTi owners are in trouble...their peak torque occurs from 1800 rpm all the way up to 5000.

Infact the perfect cruising speed of a lot of vehicles is often right at the peak torque area of the curve....not only is that the point where the engine is at its most efficient (in terms of amount of work produced that is NOT a factor of engine speed)...but the tranny is set up to milk that zone for all its worth.

[SleepyGorillaMuseum]

I was under the belief that you use the least amount of fuel when your torque is at its peak...?

[le0n]

i honestly don't see myself getting the best mpg if i cruise at 120mph in 5th gear (the 'peak' on my torque band), nor if i cruise at 60mph in 3rd gear.

so please lead me in the right direction on this, because 'my' logic has apparently misled me...

[rockfordrabbit]

i honestly don't see myself getting the best mpg if i cruise at 120mph in 5th gear (the 'peak' on my torque band), nor if i cruise at 60mph in 3rd gear.

so please lead me in the right direction on this, because 'my' logic has apparently misled me...

So you are saying that at peak torque (3750 rpm) in 5th gear you are doing 120mph?

Again, you are talking absolute nonsense.

Just look at the graph you posted...the horizontal yellow line at the top...thats the torque curve...as you can see the peak torque occurs at around 4250rpm (so its probably the curve of a MKVI Golf...not an MKV Rabbit).

Hp is the horizontal red line.
Hp= torque multiplied by engine speed divided by 5252.

So torque is engine work without the multiplication of engine speed taken into account....the engine is at its most efficient when producing its maximum work that is not dependant upon engine speed (as higher engine speed results in higher fuel consumption over a given time....as rpm literally means revolutions per second you can see why this is the case).

The torque curve has little to do with fuel consumption....higher torque does not require more fuel... higher engine speed requires more fuel over a given time....torque is a measure of rotational work in lb-ft and the curve is produced by characteristics of the engine (its stroke, bore, header airflow characteristics etc)...not by the amount of fuel being used.

As I said before engine efficiency is just part of the equation...transmission gearing and drag coefficients have a major part to play in optimal cruising speed as well.

So to sumarise (Again!!): It is pure nonsense to say that peak torque consumes more fuel and that you should stay away from that area of the graph when aiming for best mpg. The Peak torque zone is actually the most efficient part of the curve.... but there are so many other factors involved.

You get it now?...please don't make me go into more detail.

[b.a.]

knowing at what rpm you make torque really won't help you with your quest to reduce fuel consumption torque is defined as "a turning motion. It is the ability to make power, and it is defined as a tendency of force to rotate a body on which it acts"

Horse power has more of an effect on gas consumption since hp is the measure of your engines ability to preform work. but ultimatly displacement and gearing have the final say. think of it this way

your grandmas V8 buick is perfectly fine with plugging away at 70mph at an rpm of about 2k. now your brothers civic at the same speed will be pushing about 3500rpms. in theory the civic should use more gas because it takes a higher rpm to do the same amount of work as the buick... but the buick has a large displacement V8 meaning it takes a much larger amount of fuel just to turn the engine compnents now the civic has a small 4cyl engine that spools up quick and is comfortable plugging along at 3.5k rpms all day.

whats going to detemine your fuel economy with the rabbit is your ability to match you gear to the work your car has to do and your ability to keep from pressing down on the accelerater.

if you want to increase your fuel economy work out a way to get your engines thermal efficiency over 33%. and good luck with trying to do that.

[le0n]

now it get it rockford, thanks for clearing that up for me...

[SleepyGorillaMuseum]

Great post rockford. I was aware of the fact that there are many, many components when it comes to calculating best mpg. I knew that torque was one of them, which was why I asked that in the OP. Would you care to delve into possible all around solutions for maximizing mpg with the 2.5l. I'm sure this has been discussed numerous times so if someone has a link with good info, that would be great as well.

[DigitalPirate]

A couple of easy ways to increase fuel economy on our cars are:

* Reducing rolling resistance by:
1) over inflating tires (40+ PSI)
2) stiffening the suspension

* Increasing the efficiency of the engine
1) With a cold air intake
2) reducing restriction in the exhaust

[jthj]

Also, how you drive is very important. If you keep your acceleration gradual and coast to lights that are about to turn red ect you'll see a big improvement. Assuming you don't already do this.

[AcADIeN]

my experience, if you want best mpg, don't go higher than 3000 rpm before shifting, and use your cruise control to speed up. (if you have an automatic, there is not much you can do about the rpm)

I'm able to do approx 650 km per tank on the highway, and arround 550 km per tank in the city (was not able to do better, and I have my car since nov 97).

if I don't use that technic but still with a relax driving, I do 550 on the highway and 450 in the city.

if I drive like I usually do (lot of rev), its max 450 on the highway and 380 in the city.

[BadEgg]

OP - Go drive a car w/ an Inst. MPG guage. Whenever the engine is under load, the MPG will drop. Take your foot off the gas when coasting downhill, etc and the MPG will go up to 99. What does that tell you? Drive in a way that doesn't tax the engine - if your goal is best possible MPG.

- Keep speed constant on the highway.
- Coast over the crest of hills, try to speed up a little bit when coming to a hill instead of gassing it on the incline.
- Downshift when coming to off ramps and red lights. Shift early. Don't race people (esp. Honda's - waste of time/gas).
- Don't let the car warm up for a long time.
- Keep the accessories in check (don't run the heated seats or A/C longer than you have to do).

Unless you feather the clutch to keep the engine at a certain RPM (which will burn out your clutch early), what's the point of driving the car at a certain RPM to get best gas mileage? Just keep her in the highest gear for conditions, and do the speed limit. You pretty much don't have a choice anyway, except to control what gear you're running. Road conditions, traffic, and Popo will dictate how you drive most of the time anyway. But if you want to experiment, try this.

Reset the odometer. Drive like you alway do for one full tank. Fill the tank and divide your miles by gallons ( Trip mi / gal gas purchased).

Reset the odometer. Drive the next tank like you have a full cup of coffee on the dashboard and you don't want to spill a drop (throwback to License to Drive). Fill up and do the math. Compare MPG for both driving "styles."

I drive conservatively 95% of the time and have fun 5% of the time, which results in 29 MPG average. Good luck.


If that don't work for you, I hear the Prius is on sale now, and the light-blue ones are a real popular color

[SleepyGorillaMuseum]

Thanks BadEgg alot of that stuff I try to do as much as possible. All good advice except for that last bit lol. Question... Is there a best Highway crusiing speed i.e; is staying at 75mph more effiecent than cruising at 85?

[BadEgg]

Thanks BadEgg alot of that stuff I try to do as much as possible. All good advice except for that last bit lol. Question... Is there a best Highway crusiing speed i.e; is staying at 75mph more effiecent than cruising at 85?

Dude, I have no idea. Sometimes it seems I get a little bit better mileage when I'm running late and have to do 85 mph all the way down the highway (I personally hate speeding/driving fast). I usually drive mad slow so I can crank tunes. Plus, the way my car looks in the Summertime, it gets enough attention w/o breaking the law.

I would say whatever mph is 3k RPM for your Rabbit (depending on rims, x-mission, tire inflation, etc). 69~72 mph sound resonable? Unless you're in The South, then you'll get mowed down b/c the speed limit is 75 there!