Need Advice Immediately! MPG Towing Nightmare
03-17-2011, 10:29 AM
#46
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I would contest that there is a lower limit to the RPM band as well where the BSFC is going to go the other way. Just maintaining lowest RPM for best economy has been proven not to work. Again the 12V engine due to its design had a peak in the BSFC near the 2000 mark. Surprisingly thats around the 60 mph mark and nets me the best mileage.
Understanding the comparison of the 7.3LPSD my 97 also got 13 mpg in stock form, but with power additions it never comes out of OD when towing but gets 11 mpg. More power=more fuel.
Understanding the comparison of the 7.3LPSD my 97 also got 13 mpg in stock form, but with power additions it never comes out of OD when towing but gets 11 mpg. More power=more fuel.
Chris
03-17-2011, 11:37 AM
#48
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03-17-2011, 02:48 PM
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I would contest that there is a lower limit to the RPM band as well where the BSFC is going to go the other way. Just maintaining lowest RPM for best economy has been proven not to work. Again the 12V engine due to its design had a peak in the BSFC near the 2000 mark. Surprisingly thats around the 60 mph mark and nets me the best mileage.
Understanding the comparison of the 7.3LPSD my 97 also got 13 mpg in stock form, but with power additions it never comes out of OD when towing but gets 11 mpg. More power=more fuel.
Understanding the comparison of the 7.3LPSD my 97 also got 13 mpg in stock form, but with power additions it never comes out of OD when towing but gets 11 mpg. More power=more fuel.
Well, it depends on which engine you're talking about. In the case of a 2008 Dodge, BSFC is constant along the torque curve from 1800rpm to any lower RPM you'd consider running.
Obviously, this doesn't necessarily apply to other engines or even other years of CTD.
For example, my '02 has lowest BSFC at 2000 rpm. But that doesn't mean I get better mpg going 72 instead of 65. The difference in BSFC points is just too small to matter compared to the difference in engine loaded (and hence, demanded fueling).
JH
03-17-2011, 04:45 PM
#50
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I guess where I was going is that for static variables of road speed (resistance) and engine load that just advancing to the highest gear ratio to minimize engine RPM is not the best economy for the engine and over a distance would negatively affect fuel economy. Now for the newer HPCR engine, that range of RPM is more broad and I understand that.
Anyone towing an RV will notice how much the fuel gauge is inverse to the speedo and keeping the speed down near the 60 mph mark and below drastically increases fuel economy. So those factors do affect the mileage more that what we are discussing WRT BSFC.
Driving around empty at an idle with no resistance would obviously reduce fuel consumption, I don't contest that.
Anyone towing an RV will notice how much the fuel gauge is inverse to the speedo and keeping the speed down near the 60 mph mark and below drastically increases fuel economy. So those factors do affect the mileage more that what we are discussing WRT BSFC.
Driving around empty at an idle with no resistance would obviously reduce fuel consumption, I don't contest that.
03-19-2011, 06:16 AM
#51
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Not to sound dumb but what does BSFC & HPCR stand for ?
The sweet spot on my '03 is 2100 and i get between 9.5 - 11.9. I have found the overhead to be real close if i reset it evertime I fill up. Most of the time I reset it at the beginning of the trip to get the trip average.
John
The sweet spot on my '03 is 2100 and i get between 9.5 - 11.9. I have found the overhead to be real close if i reset it evertime I fill up. Most of the time I reset it at the beginning of the trip to get the trip average.
John
03-19-2011, 07:48 PM
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my previous cummins an 01 dually 6spd 4:10's 4in to 5in stacks got 12 14 all the time empty loaded i ran 68 all the time my new 08 with 3:42 6spd srw gets 23 empty 12 loaded running 80 and its all stock
03-21-2011, 09:21 AM
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Yeah, 23mpg @ 80mph is NOT going to happen with these trucks...too heavy, too much wind.
I think I could squeak 20 out of mine now after deletes on an all highway trip, but my last mixed tank was 16.4mpg.
Chris
I think I could squeak 20 out of mine now after deletes on an all highway trip, but my last mixed tank was 16.4mpg.
Chris
03-21-2011, 10:46 PM
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Chris, i dont understand your previous statement. You preach your 3.42's are so much better than a lower ratio and your fuel mileage reflects that. I have 4.10's and all highway flat ground i can just touch 20 mpg at 67 mph (hand calculated). Hills where i normally drive is around 18 highway.
You can argue that you may be able to drive faster, 75 or so and get that mileage, but if you have to tow in fifth at around 2200 rpms as you have previously stated, you arent getting better mileage overall. I can also argue i can tow at a lower rpm then you which makes your argument null and void. i guarantee that us with 4.10's dont have to tow in 5th, In addition we can tow thru hills in 6th, do it with heavy loads and not strain the tranny.
I dont care that you tow 30k as im not interested in that foolishness.
I wouldnt care to try with my srw, not that i doubt it would pull it but common sense comes in to play here.
So Please explain to me how your 3.42's are that more efficient at both towing and empty? Were you the one who said 4.10's are for gassers, or was that someone else?
You can argue that you may be able to drive faster, 75 or so and get that mileage, but if you have to tow in fifth at around 2200 rpms as you have previously stated, you arent getting better mileage overall. I can also argue i can tow at a lower rpm then you which makes your argument null and void. i guarantee that us with 4.10's dont have to tow in 5th, In addition we can tow thru hills in 6th, do it with heavy loads and not strain the tranny.
I dont care that you tow 30k as im not interested in that foolishness.
I wouldnt care to try with my srw, not that i doubt it would pull it but common sense comes in to play here.So Please explain to me how your 3.42's are that more efficient at both towing and empty? Were you the one who said 4.10's are for gassers, or was that someone else?
03-21-2011, 11:48 PM
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Yikes, something must be wrong with my truck, 23 mpg ? 15,000 miles and no where near that .... whats the secret because at 3.75 a gallon I am interested in doing whatever I can to improve my mileage !
03-22-2011, 07:51 AM
#59
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I averaged 12-14mpg towing my 12k RV last year. The first 10k, the truck was a fuel pig, after that the power came up and got better fuel mileage. The fresh engine and 4.10 gears aren't helping you to much. My 02 gets around 12-13mpg towing the same trailer. I tow around 60-70mph. My fuel mileage is calculated off my garmin GPS. Unloaded I get 18-20mpg out of the 10 and 17-18mpg out of the 02. These fuel consumptions are using summer fuel and no winter idling warm-up cycles.
Best fuel mileage I got was 22mpg, at 55mph going from Calgary to Vancouver.
Best fuel mileage I got was 22mpg, at 55mph going from Calgary to Vancouver.
03-22-2011, 08:16 AM
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Chris, i dont understand your previous statement. You preach your 3.42's are so much better than a lower ratio and your fuel mileage reflects that. I have 4.10's and all highway flat ground i can just touch 20 mpg at 67 mph (hand calculated). Hills where i normally drive is around 18 highway.
You can argue that you may be able to drive faster, 75 or so and get that mileage, but if you have to tow in fifth at around 2200 rpms as you have previously stated, you arent getting better mileage overall. I can also argue i can tow at a lower rpm then you which makes your argument null and void. i guarantee that us with 4.10's dont have to tow in 5th, In addition we can tow thru hills in 6th, do it with heavy loads and not strain the tranny.
I dont care that you tow 30k as im not interested in that foolishness. I wouldnt care to try with my srw, not that i doubt it would pull it but common sense comes in to play here.
So Please explain to me how your 3.42's are that more efficient at both towing and empty? Were you the one who said 4.10's are for gassers, or was that someone else?
You can argue that you may be able to drive faster, 75 or so and get that mileage, but if you have to tow in fifth at around 2200 rpms as you have previously stated, you arent getting better mileage overall. I can also argue i can tow at a lower rpm then you which makes your argument null and void. i guarantee that us with 4.10's dont have to tow in 5th, In addition we can tow thru hills in 6th, do it with heavy loads and not strain the tranny.
I dont care that you tow 30k as im not interested in that foolishness.
I wouldnt care to try with my srw, not that i doubt it would pull it but common sense comes in to play here.So Please explain to me how your 3.42's are that more efficient at both towing and empty? Were you the one who said 4.10's are for gassers, or was that someone else?
20mpg with 34x11x20's?? What's your effective final drive ratio now? Very close to mine...maybe 150RPM difference at 67mph
Why am I not getting better mileage overall? I can run in 6th no problem with all but the heaviest of loads I haul...power is not the problem, the questionable reliability of the 68RFE is, which is why I CHOOSE to run in 5th gear. I never once have said I HAD to tow in 5th....hills, flat ground, empty, loaded, whatever....this is a Cummins, remember
4.10's are for gassers, with the exception of larger tires on trucks....if I knew I was going to change my tire size, I would have ordered something other than 3.42...since I have grown past big noisy tires (at 25 years old), I picked the gearing that I thought would do the job I needed, and get be the best mileage when empty. I've done that.
And as far as my common sense, I'll leave that alone as I do like this forum, and I don't intend on losing my privilege of being allowed to discuss trucks here...I'll just say that at 25 years old, I have logged about 45-50K miles a year for 10 years now, most of them towing with not one incident. My common sense works much better than a lot of other drivers on the road, and since you have never met me, ridden with me, or seen me tow anything, you have no idea if it's done safely or not. In the days of rising fuel prices, and with more miles to cover to keep these farmers happy and their machines running, we have to do what we have to do. We also can not get a Class 8 truck into a lot of farms and places we need to get into.....but I guess according to you we should just treat them like a car dealership and tell them to have it towed in?
Chris