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Old 04-06-2020, 02:31 AM   #21 (permalink)
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Quote:
Originally Posted by hat_man View Post
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?




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Old 04-07-2020, 02:09 PM   #22 (permalink)
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Quote:
Originally Posted by Ecky View Post
That's probably true with fixed gearing, because load is *probably* more important than piston speed in the vast majority of cases.

But, let's say you have a hybrid vehicle, which can spin the engine at whatever RPM, and toggle it on and off whenever. Is it going to be more efficient to spin the engine at, say, 3000rpm 90% load for 30 seconds out of every minute, or to spin it at 1500rpm 90% load and leave it running all the time?
This is basically the difference between 40mpg in the Prius and 60mpg in the Prius. If... Its warm enough and the cars warm up protocol doesn't sabotage me.
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Old 04-08-2020, 02:46 PM   #23 (permalink)
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Quote:
Originally Posted by 2016 Versa View Post
My Versa with CVT seems to get it's best mileage between 1400-1600 RPM and depending on terrain is usually 40-50 MPH.
I think it is important to remember that mileage (fuel Economy) and volumetric efficiency are not the same. You may get your best mileage in specific freeway conditions at 40-50 mph and 1400-1600 rpm. However, Frank's formula applied to your 2016 Versa with its 3.29 inch piston stroke should be moving at a rate of about 1100 ft/min at 2000 RPM. That might be your greatest volumetric efficiency. But if you drove 65 mph or more to cruise at 2000 rpm your aero drag would be MUCH higher and you fuel economy would suffer.
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Old 04-09-2020, 06:24 AM   #24 (permalink)
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Yep, actual results trump theory every time.

We seem to be seeing this in action as the predictive models are embarrassed by actual results during the current pandemic.

Could Global Warming modeling be far behind? :-)
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Old 04-15-2020, 05:25 AM   #25 (permalink)
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The best mileage so far, for a long distance (150 miles) was 71 MPG
The second best mileage I achieved for a very long distance (400 miles) was 68 MPG. Those MPG's are real MPG's, measured at the fuel pump.

Both distances were traveled at speeds between 55 and 60 MPH at 1750 - 1900 RPM in 5th gear. The car is not yet modified.

I recon that lower speeds will increase the mileage a little. However, the highest gear is quite long for the tiny three cilinder diesel engine, and lower speeds will make the engine hum with greater load.

The very very best mileage could probably be achieved in 4th gear at 35 - 40 MPH? Less drag at those speeds.
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Old 04-15-2020, 07:39 AM   #26 (permalink)
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Quote:
Originally Posted by GreenTDI View Post
The best mileage so far, for a long distance (150 miles) was 71 MPG
The second best mileage I achieved for a very long distance (400 miles) was 68 MPG. Those MPG's are real MPG's, measured at the fuel pump.

Both distances were traveled at speeds between 55 and 60 MPH at 1750 - 1900 RPM in 5th gear. The car is not yet modified.

I recon that lower speeds will increase the mileage a little. However, the highest gear is quite long for the tiny three cilinder diesel engine, and lower speeds will make the engine hum with greater load.

The very very best mileage could probably be achieved in 4th gear at 35 - 40 MPH? Less drag at those speeds.
US or UK gallons? Care to start a fuel log? Which vehicle exactly?

Wish we had 3 cylinder diesels here.
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Old 04-15-2020, 08:02 AM   #27 (permalink)
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For me it's 1100 RPM.
My Insight refuses to drop RPM below 1100 RPM and the CVT maxes out ('top gear') at 50 km/h per 1000 RPM, so I get best economy driving 55 km/h @1100 RPM.
In nice weather that can be 35 to 40 km per liter (80 - 92 MPG)...!

60 km/h @1200 RPM is hardly any worse though, but it climbs ever faster with more speed. Anything above 80 km/h (50 mph) @1600 RPM hurts a lot.
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Last edited by RedDevil; 04-15-2020 at 09:15 AM..
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Old 04-15-2020, 08:51 AM   #28 (permalink)
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Quote:
Originally Posted by Ecky View Post
US or UK gallons? Care to start a fuel log? Which vehicle exactly?

Wish we had 3 cylinder diesels here.

US gallons, I'm converting the km/l that we use into MPG (US) The car is a Skoda Fabia Estate with the 1.2 CRTDI engine, which is a VAG product and similar to the Volkswagen Polo.
I'm certainly going to start a fuel log here. Fact is that I don't drive a lot right now because of the virus lockdown …
I have some fueling data from a couple years ago on spritmonitor.de
https://www.spritmonitor.de/en/detail/465392.html
The car is definitely more economically now than those first 5 years.

Edit: link of my early fuel log in my signature
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Last edited by GreenTDI; 04-15-2020 at 09:05 AM..
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Old 05-05-2020, 10:28 AM   #29 (permalink)
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In nearly all the road vehicles I've owned, best MPG is around 1500-1600 RPM. That's where the torque curve gets fat, but low enough in RPM to keep the fuel consumption down.
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Old 05-05-2020, 02:00 PM   #30 (permalink)
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This probably depends alot on overall engine design. While done for reasons other than MPG, my engine is destroked and has large custom cams and much higher than stock static and dynamic compression; yet it seems to run best/most efficient between 2700 and 3000 RPMs (compared to about 2500 RPM stock). My piston design is kind of terrible for DI, though, so I'm sure that's costing me quite a lot of efficiency; I have yet to implement piggyback PI and/or WMI so it remains to be seen if going to a full time hybrid fueling setup can reclaim any of that.

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