best speed for fuel economy - Printable Version
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best speed for fuel economy - encantotom - 09-14-2012
i thought it would be an interesting thread to provide data on what speed provides the best fuel economy for different engines used in our newells
i will start with some speculation on my series 60. i have read that the optimum rpm for best efficiency is 1400 on a 12.7L series 60.
i had taken a few pictures of my vmspc while driving so had a couple of data point.
70mph was 1566 RPM on a snapshot i had taken. from another one it was ~ 11 RPM per MPH in 6th gear.
so to hit 1400 RPM i would need to be at ~55 MPH.
i tend to drive in the mid 60's typically. i heard somewhere else that MPG goes up about 1 MPG for every 10mph you slow down if you are driving 55-75mph. i got about 7.4mpg on my 4300 mile trip. lots of long grades and hills on it and pulling a car.
any other data on this and for other engines as well? i know on my 8v92 i seemed to get about 6.5mpg no matter what i did...
discussion?
tom
RE: best speed for fuel economy - rheavn - 09-14-2012
My experience is that if you slow down much below mid 60s, unless you are on perfectly flat road, you will experience a lot more shifting. That will burn up any increase you gained by slowing down. I also believe that using cruise control will improve mileage.
RE: best speed for fuel economy - RussWhite - 09-14-2012
I challenge our back to back coaches to a mileage run - you on cruise and me on my throttle. Whoever runs out of fuel first is a big looser :-)
Are you at Bella Terra? Have fun! Russ
RE: best speed for fuel economy - rheavn - 09-14-2012
Sounds good to me! 165,000 miles of driving electronically controlled diesels has proved to me that you will experience less shifting, therefore better mileage, letting the computer control the speed. Yes we are at Bella Terra. Weather has been perfect!
RE: best speed for fuel economy - RussWhite - 09-14-2012
A geek like me thinking I can beat the computer - what has happened to me! I think my edge may rest with what we call "feed forward" in engineering terms. The ability to anticapte the future ( coming terrain ) and adjust for what is ahead. I think it would be interesting.
So glad to hear all is well at Bella Terra. There are no guarantees this time of year and so pleased it worked out. Hi to Suzy!
RE: best speed for fuel economy - Express1 - 09-14-2012
(09-14-2012, 11:33 AM)rheavn Wrote: Sounds good to me! 165,000 miles of driving electronically controlled diesels has proved to me that you will experience less shifting, therefore better mileage, letting the computer control the speed. Yes we are at Bella Terra. Weather has been perfect!
Steve, Perfect weather? really? Not just a little HOT?
RE: best speed for fuel economy - rheavn - 09-14-2012
Matt,
Mid 80s, with little humidity, is not hot after an entire summer of 90s & 100s
Russ,
I am amazed how well the computer does at anticipating grades and adjusts. Running I-40 to Cal the coach downshifts just a handful of times. Seems like the engine computer can anticipate additional load quicker than I would. And does so much smoother. Whenever I have tried to go off the cruise control, I feel like I'm playing catch up which causes additional shifting. On the other hand an engineer designed the system so I guess an engineer would be the one to beat the system. I'm just not that smart.
RE: best speed for fuel economy - RussWhite - 09-14-2012
I'm pretty sure I can see that hill coming before the computer can - Ha
RE: best speed for fuel economy - Richard - 09-14-2012
On some of the bus conversion forums, they make reference to the DDEC responding differently when the cruise is on. It is actually possible, and common, that the engine is programmed to have more HP and torque when on cruise to encourage the truckers to run on cruise (aka to drive the speed limit)
I swear my engine pulls hills on the cruise without shifting, that it will not pull without shifting when I am the cruise control.
RE: best speed for fuel economy - Express1 - 09-14-2012
(09-14-2012, 05:48 PM)Richard Wrote: On some of the bus conversion forums, they make reference to the DDEC responding differently when the cruise is on. It is actually possible, and common, that the engine is programmed to have more HP and torque when on cruise to encourage the truckers to run on cruise (aka to drive the speed limit)
I swear my engine pulls hills on the cruise without shifting, that it will not pull without shifting when I am the cruise control.
Richard, I took note of that today going west on I80. Now doubt with cruise off and mode button on, performance feels stronger..
