mpg? altitude issues?
Junior User
Joined: Nov 2010
Posts: 54
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From: Weaverville, CA
We live at 2000 feet. Over the first 1000 miles my 6.7 is averaging 13.8 mpg. While running on the flat interstate, I was able to get 15.9 mpg while travelling 74 mph. I have no idea how guys are getting 18 mpg. The power of this motor is incredible. I didn't upgrade to it for the MPG.
Senior User
Joined: Nov 2010
Posts: 376
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From: Tempe, AZ
Joe
Junior User
Joined: Nov 2010
Posts: 54
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From: Weaverville, CA
I don't know if we are buying winter diesel. There is no indication on the pumps at my station. We are in Northern California. Like I said, mpg is not a big factor to me. I only put about 10,000 miles a year on my pickup. It wont hurt my feelings if the mpg goes up 10% in the summertime.
Cross-Country
Joined: Sep 2010
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That is a good estimate... It is generally accepted that gas engines lose 5% of their power for every 1,000 feet in elevation- That's why at 8,000 feet a gas vehicle has literally "run out of gas" since it has essentially lost 40% of it's power. On the same note, turbo-charged ... are less affected by elevation and lose about half of a normally aspirated gas engine, or about 20% at 8,000 ft elevation.
This is almost entirely to do with the turbocharger, especially the compressor's A/R and airflow characteristics. Installing a turbo that is absolutely 'perfect' for a vehicle's requirements at sea level, for example, will make that turbo significantly undersized for 10,000 feet, and thus very inefficient up there. The opposite circumstance can also happen/be true. The thing is, once you reach the altitude at which a given turbo 'maxes out,' so to speak, the engine's power output will drop _faster_ than a naturally aspirated engine from there on up. At least, that's my experience with them.
Postmaster
Joined: Apr 2009
Posts: 3,839
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Keep in mind the truck did not slow to a stop on the big hill. IIRC it crested the hill at 40 plus mph. Also remember they started from a dead stop on the side of a major expressway at 8000 feet elevation.
The turbo is not sized for maximum power at sea level. Ford tested both turbo's during development and testing, yes the same exact turbo on the GM. Their decision to use the current turbo was based on a number of performance and fuel economy test results. They do need to do some fine tuning though...hope to see it soon.
Regards
The turbo is not sized for maximum power at sea level. Ford tested both turbo's during development and testing, yes the same exact turbo on the GM. Their decision to use the current turbo was based on a number of performance and fuel economy test results. They do need to do some fine tuning though...hope to see it soon.
Regards
Post Fiend
Joined: Jul 2005
Posts: 6,127
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All things considered, a larger diameter turbo, holding everything else constant, will result in slightly slower boost (acceleration) but better top end performance.
Compromises need to be made for the majority of users, who do not tow uphill at 8,000ft and above.
There is nothing that can be done to reduce how a bigger turbo will spool up slower (and soak up more energy) than an identical smaller turbo.
Mass is mass.
My fig Newton's worth.
Compromises need to be made for the majority of users, who do not tow uphill at 8,000ft and above.
There is nothing that can be done to reduce how a bigger turbo will spool up slower (and soak up more energy) than an identical smaller turbo.
Mass is mass.
My fig Newton's worth.
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Cross-Country
Joined: Sep 2010
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I like Fig Newtons, too!
I'm sure you're right that the stock turbo wasn't sized for 'perfect' at sea level. Your comments on 'performance' and mpg testing being a factor in selecting turbo sizing and trims are well taken, too, and translate into: the turbo is certainly sized for elevations closer to sea level than 10,000 feet. Given the fact that most pickups, even diesels, are primarily personal transportation devices (even commuter vehicles) just like a Ford Focus, this kind of trade-off makes sense. We don't have any complaints about our trucks, thus far, operating from ~4800 - 7500 feet, but then again we haven't any other diesel pickups with which to compare. We've not been disappointed with the performance of our 8.1-liter Chevys nor V-10 Fords, but the smaller engines are real dogs up here.
I'm sure you're right that the stock turbo wasn't sized for 'perfect' at sea level. Your comments on 'performance' and mpg testing being a factor in selecting turbo sizing and trims are well taken, too, and translate into: the turbo is certainly sized for elevations closer to sea level than 10,000 feet. Given the fact that most pickups, even diesels, are primarily personal transportation devices (even commuter vehicles) just like a Ford Focus, this kind of trade-off makes sense. We don't have any complaints about our trucks, thus far, operating from ~4800 - 7500 feet, but then again we haven't any other diesel pickups with which to compare. We've not been disappointed with the performance of our 8.1-liter Chevys nor V-10 Fords, but the smaller engines are real dogs up here.
Postmaster
Joined: Apr 2009
Posts: 3,839
Likes: 2
I like Fig Newtons, too!
I'm sure you're right that the stock turbo wasn't sized for 'perfect' at sea level. Your comments on 'performance' and mpg testing being a factor in selecting turbo sizing and trims are well taken, too, and translate into: the turbo is certainly sized for elevations closer to sea level than 10,000 feet. Given the fact that most pickups, even diesels, are primarily personal transportation devices (even commuter vehicles) just like a Ford Focus, this kind of trade-off makes sense. We don't have any complaints about our trucks, thus far, operating from ~4800 - 7500 feet, but then again we haven't any other diesel pickups with which to compare. We've not been disappointed with the performance of our 8.1-liter Chevys nor V-10 Fords, but the smaller engines are real dogs up here.
I'm sure you're right that the stock turbo wasn't sized for 'perfect' at sea level. Your comments on 'performance' and mpg testing being a factor in selecting turbo sizing and trims are well taken, too, and translate into: the turbo is certainly sized for elevations closer to sea level than 10,000 feet. Given the fact that most pickups, even diesels, are primarily personal transportation devices (even commuter vehicles) just like a Ford Focus, this kind of trade-off makes sense. We don't have any complaints about our trucks, thus far, operating from ~4800 - 7500 feet, but then again we haven't any other diesel pickups with which to compare. We've not been disappointed with the performance of our 8.1-liter Chevys nor V-10 Fords, but the smaller engines are real dogs up here.
Last edited by rickatic; Feb 15, 2011 at 04:51 PM. Reason: Redundant
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