What RPM range do YOU get the best mileage at?
 

Is there a general rule of thumb for better/best FE in certain RPM range?

For my Ranger it's around 2k rpm. That's 55 mph in 5th gear. At 1900 rpm the engine really gets smooth but I can't drive that slow on the highway without causing other drivers to have some "road rage".

I know there are a lot of factors that go into FE. Things like speed, gearing, tire size, etc. And that all vehicles are different. Things like weight, aero, drive train (FWD/RWD/AWD), etc. And where we drive them most often, either in town or on the highway.

So where do YOU get YOUR best mileage?

I use 1000-1200 ft/mn piston speed as optimal efficiency zone. I have not personally tested it but several sources that seem legit to me point in that direction.

As slow as possible. With both my current 2.4L engine and the previous 1.0L engine, it would peak around 30mph and remain nearly constant until ~50mph, where it would begin to drop pretty rapidly.

1.0L engine: 1075rpm - 1720rpm
2.4L engine: 975rpm - 1560rpm

You ask a question, then give your answer that doesn't fit the question. You are adding speed into the equation when you are looking for peak miles per gallon or liters per 100 km or however you measure fuel economy. If it happens at 35 mph, then it happens at 35 mph. If 35 mph isn't allowed on say an interstate, that doesn't mean that your peak efficiency now happens at 55 mph.

To answer the question for my TDI touareg I'd say right about 38 mph in 7th gear which puts me at about 1300 rpm and it goes over 40 mpg on a steady level road, and that's with winter fuel. The problem is, I can't force the shift to 7th gear until I'm goin over 40 mph so I have to get it up to 41, shift to 7th, and then let it drop back down to 38. If I go as low as 35 mph it will probably shift back into 6th with any addition of throttle. It still gets pretty good economy at 55 mph and will run in 8th gear there but it's more like high high 30's mpg vs into the 40's. At 65 it's dropped into low 30's

Unfortunately most vehicles can't divorce RPM from speed, and it seems to me a rare case where going faster in top gear actually improves economy.

How do you calculate/track that while driving? Is there a formula? Seems like you'd need a variety of piston and stroke data as well as RPM.

To the OP: my preferred shift ranges are 1500-2000 rpm or 1700-2200 rpm, and I kinda use the latter more often. My fav cruise option on the freeway is 60 MPH @ about 1900 rpm. At that speed I can get high 60s mpg on average. But I often do pulse and glide on the freeway, using 55-65 mph, 55-70 mph, or 60-70 mph speed ranges.

at 45MPH = 40-45mpg reading on the instant gauge @1,080rpm
3.0L/6.0L V8 engine btw.. once it flips to v8 mode it drops to 25-29mpg but soon will shift back to v4 mode and 40-45mpg..

the best ever was 31.5mpg


I just reset my MPG average it's at 30MPG avg in 4 miles of travel..


the reason for resetting it as my suv have some issues with a dirty power cable causing issues with the engine. =poor mpg my fill up was only 18.9 but i did idle and short trips = lost mpg it probably would have been in the 22-25 mpg range otherwise

I have found that for large v6 engines of the american style. (3.0-4.X L) anywhere from 1200-2700 RPM are within a couple % of peak BSFC.
I really tested this out on the Ranger when I only had 1,2, and 5th. I would drive anywhere from 1st to 2700 RPM at 90% load, 2nd to 3000 RPM at 90% load, then shift to 5th and hit about 1075 RPM at 30 mph and continue increasing speed at 90% load to 45 mph. (28" tire and 3.73s) Then I would just stay in 5th and cruise around at 45 mph since that is the speed limit here. A little pulse and glide with EOC and what not, DWB up to stop signs. I did note that you get charging issues doing that and wouldn't dare use the starter. I actually had a tank of cruising around town at 25 mpg for about 100 miles on a stock 1996 Ford Ranger 3.0 5 speed with EGR issues, vaccum leaks, and more sensor issues. Been working on getting the transmission back in it now that Quarantine has hit and I have more free time. It has been one hell of a pain in the ass!

*I think skip shift is the way to go on these bigger non 4 cylinder engines. Going gear to gear at 90% load on the bigger stuff is a little too brisk for me versus how slow the old 96 civic was at doing it.

Get the stroke then online calculators can tell you the rpm range that 1000-1200 ft/mn piston speed is. If your car has a tach you are now golden. If not then you need gear ratios and tire size and another online calculator to spit out the ideal speed range in top gear. Incidentally most of my cars don't have tachs so that is how I did it, and they usually calc out to be in the 45 to 50 mph area.

Stroke differences are how a large engine can be putting along and a tiny engine can be screaming and they will both be at the same piston speed and optimal efficiency range.

This is a very good approximation at high load, but cars that are geared way too short or have really overpowered engines do better if you run them on the slower side.