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 > Your search for posts made by '4x4ord' found 578 matches.

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RE: Why diesels are most efficient around 1,800 rpm

"When towing, whatever gear keeps engine rpm between 1,800 and 2,000 rpm will give the best fuel mileage and power because that is the rpm window where the Cummins 6.7-liter makes peak torque. I tow at 60 with rpm's about 1,750. Just right! That's with 4.10's. At 70 I am about 2,000. With my last DRW I had 3.42's. I would tow in 5th at same rpm's as above, just right! Exactly right Exactly wrong. The 6.7 cummins only makes it's peak torque at wide open throttle and full boost at that rpm and I'm pretty sure no one drives down the highway at wide open throttel. Fish, I believe you are misunderstanding what is being said here. Generally, engines are more efficient under load around the rpm that they make peak torque. This is actually true for most engines. They are not saying to drive around at WOT. I guess I'm having a hard time wrapping my head around this. Diesel engines make peak power at WOT and full boost, and typically are most fuel efficient at minimum boost. I'm not sure how that can happen at the same ~ rpms. It is not about making peak torque. They are just talking about the rpms at which it makes that peak torque. This is basically what 4x4Ford have been arguing. Towing my 13k 5ver at 65mph would put be at in 6th which is the yellow line below. The red line is about where I am in 5th gear. As you can see, under medium to heavy loads for my gear ratio, I am closer to or actually in the "sweet spot" they were talking about which happens to be around where my engine makes peak torque. https://i.postimg.cc/05YMn9sQ/BSFC.png height=550 width=400 I like the way you do your graphs. I'd like you to draw a line showing the rpm and torque output of your engine while pulling your trailer from 60 to 70 mph in both 5th and 6th gear. What kind of fuel economy do you get at 60 vs 70 and 5th vs 6th gear?
4x4ord 10/25/20 05:44pm Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

"When towing, whatever gear keeps engine rpm between 1,800 and 2,000 rpm will give the best fuel mileage and power because that is the rpm window where the Cummins 6.7-liter makes peak torque. I tow at 60 with rpm's about 1,750. Just right! That's with 4.10's. At 70 I am about 2,000. With my last DRW I had 3.42's. I would tow in 5th at same rpm's as above, just right! Exactly right I’ll expect to be getting the 3:31s in my next truck. Whether I’ll have to lock out 9th or tenth will depend on the load I’m pulling but with 1050 lb ft of torque most my loads will be considered light. It not a factor of engine power. I can and have towed my camper many times on my level three tune which puts me at around 470 hp/1,020 lb-ft at the wheels which is about 540 hp/ 1,175 lb-ft at the crank with the standard 15% loss from the drivetrain. These were my dyno numbers with my stock turbo and they are probably 30-50 hp more than that with my current turbo, but I haven't put it on a dyno yet to verify. I still have one more level on my CSP switch that will put me well over 500hp/1,100 at the wheels. So as I have been saying over and over and over..... my truck has more than enough power to tow in 6th and would blow that 1,050 lb-ft PSD out of the water. It just gets better fuel economy in 5th than 6th towing my 13k RV since it puts me at a more efficient rpms (@ 1,800) at the speeds I tow which is backed up by the BCFC map I posted earlier. I feel sorry for you that you refuse to believe that. I will also say that 6th gear in my trans is the same ratio as 10th in the Ford trans. So if I did have a hard time holding 6th with the power that my 3.42 rear geared truck makes, then you would definitely have a hard time holding 10th in a 3.31 geared truck with less power. What kind of fuel economy do you get towing your trailer with the custom tune? If you look at the BSFC map you posted you see that the stock Cummins is similar to most diesel engines in that when you are only requiring a fraction of peak HP you get better fuel economy running low rpm and higher torque. If an engine is capable of 1050 ft lbs of torque at 1800 rpm and only 380 lb ft are required to tow the trailer at 1800 engine rpm and 60 mph, it would be running way off its peak cylinder pressure at that rpm. Better to slow it down.
4x4ord 10/25/20 05:40pm Tow Vehicles
RE: comfortable ride in an one ton dually??

You could try one of these:Air ride seat
4x4ord 10/25/20 06:31am Fifth-Wheels
RE: Time to retire the 7.3 OBS?

If you buy another old used truck you could end up needing to spend money on it as well. If you sell it in non running condition it won’t be worth as much as it is after fixing it. I’d fix it. It will likely go another 15 years if you need it to.
4x4ord 10/25/20 05:25am Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

"When towing, whatever gear keeps engine rpm between 1,800 and 2,000 rpm will give the best fuel mileage and power because that is the rpm window where the Cummins 6.7-liter makes peak torque. I tow at 60 with rpm's about 1,750. Just right! That's with 4.10's. At 70 I am about 2,000. With my last DRW I had 3.42's. I would tow in 5th at same rpm's as above, just right! Exactly right I’ll expect to be getting the 3:31s in my next truck. Whether I’ll have to lock out 9th or tenth will depend on the load I’m pulling but with 1050 lb ft of torque most my loads will be considered light.
4x4ord 10/24/20 11:41am Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

Yup that was kind of stupid of me ..... sorry Shiner if you took offence. I’m certain if Shiner took a ride in one of our big trucks he’d see those engines are happier at 1300 rpm than they are at 1800 under light loads. Certainly the operator is happier.
4x4ord 10/24/20 08:35am Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

Did you notice that by dropping from 6th to 5th and slowing down from 65 mph to 55 mph he said his engine rpm increased from 1401 to something like 1565. Cummins says slowing down should have gained him 1 mpg for the lower wind drag and Shiner says he should gain some fuel economy speeding his engine up a bit. Combined you’d expect a fairly significant gain. Turns out it was only a gain of .4 mpg. I thought the Cummins rock solid rule of gaining 1mpg sounded reasonable but my take away would be that the gear drop hurt a bit so the net gain was only .4 mpg.
4x4ord 10/23/20 11:47pm Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

Sounds like this guy likes to tow in 5th for many of the same reasons as Shiner but he does indicate he gets slightly better fuel economy in 6th. He might have slightly bigger tires? Seems like splitting hairs to me. I’m certainly going to go for the quieter cab with the lower rpm if I can save a few pennies at the pump. If the transmission needs to be babied to handle towing light why not just buy a Ford? Link
4x4ord 10/23/20 04:53pm Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

Commenting on Fish's video: It's kind of hard for me to have a whole lot appreciation for a guy's comments who is blown away by the fact that he got better fuel economy when he slowed down.
4x4ord 10/22/20 07:06pm Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

Shiner I really don't think we are that different in how we understand things. For one thing I am giving the Ram/Cummins engineers a bit more respect than you do. I believe with today's technology it is not that difficult for an engineer to program a transmission to select the right gear for the load being towed. The truck computer has a lot more information to base things on than you do. Based on what you have posted I would likely lock out 6th gear with your truck if I was towing 13k at 60 mph. If I was towing at 65 mph I would definitely be in 6th unless the terrain, wind or traffic conditions were such that the tranny was shifting back and forth. Between 60 and 65 I really doubt it would make much difference what I did.... According to the BSFC map that you posted the fuel economy would be the same.... Likely about 9.5 mpg.
4x4ord 10/22/20 01:20pm Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

Funny how even TrailerLife.com even states that around 1,800 is the best rpm for fuel economy. I guess they are wrong too along with the Cummins engineers. Diesel Tech Q&A: Axle-Ratio Selection "When it comes to fuel economy, running empty around town or when driving where speeds are less than 55 mph, you’d see very little difference in fuel mileage between the two axle ratios because the transmission will never get the engine rpm high enough to be a factor. When towing, whatever gear keeps engine rpm between 1,800 and 2,000 rpm will give the best fuel mileage and power because that is the rpm window where the Cummins 6.7-liter makes peak torque. With a little time, you’ll find the engine’s “sweet spot” with the trailer you are towing. The difference in towing mpg between the 3.42 and 3.73 gears at highway cruise speed, under the same conditions, should be less than 1 mpg because of the slightly higher rpm running 3.73s. Vehicle speed actually plays a bigger role in fuel economy than engine rpm. That’s because towing or unladen, mpg drops exponentially at speeds above 60 mph, which is when aerodynamic drag (Cd) really begins rearing its ugly head related to pickups." I'd be willing to bet the Cummins/Ram engineers have got things set up so that their 400 HP 6.7 Cummins/Aisin will tow light loads, such as a 13k fiver on a level road, at 1500 rpm before downshifting to 5th and towing at 1833 rpm.
4x4ord 10/22/20 12:06pm Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

"When towing, whatever gear keeps engine rpm between 1,800 and 2,000 rpm will give the best fuel mileage and power because that is the rpm window where the Cummins 6.7-liter makes peak torque. I tow at 60 with rpm's about 1,750. Just right! That's with 4.10's. At 70 I am about 2,000. With my last DRW I had 3.42's. I would tow in 5th at same rpm's as above, just right! Sounds just right. What is your fuel economy at 60 mph and 30,000 lbs combined? How many lb ft of torque was your last DRW?
4x4ord 10/22/20 11:51am Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

The facts from the manufacturers is that they have been adding gears to the transmissions so that they can pick the best rpm for the load on the engine to obtain better fuel economy. I realize the 6.7 diesel and any other engine have their own BSFC graphs and that to get best efficiency the engine would run in a sweet spot. I can see from the graph that you posted that the 6.7 engine is most efficient when running from about 1500 rpm and producing 130 hp to something like 225 hp at 1600 rpm and at1800 rpm it is most efficient producing between 150 and 225 hp. The reason I’m asking you for your actual measured mileage is because I would like to see where your truck fits on that graph when towing your rv.
4x4ord 10/22/20 03:09am Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

My fuel economy is roughly .5-1 mpg on average.. I would say a 1 mpg savings is significant if you’re actually getting 6 mpg in 5th and 5 mpg in 6th. If on the other hand you’re getting 13.5 in 5th and 14 in 6 th .... it’s still something but I know I find I can get a difference of more than that between two trips leaving the transmission in drive both times. Anyway, what you actually measured for fuel economy in each gear really is relevant to our discussion. Did you set the cruise at 65 mph each time? Was the wind each time from the same direction and speed?
4x4ord 10/21/20 08:40pm Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

^^^ if the engine is not loaded heavy it won’t be lugging. Check your boost pressure. When a turbo diesel is pulling hard at a low rpm the turbo will be producing high boost pressure.
4x4ord 10/21/20 05:34pm Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

When that engine is working at 1800 rpm and just up to the dark blue sweet spot as you call it it is putting out a minimum of 150 horsepower. (440 lb ft of torque) According to the graph it would be burning 7 gallons of diesel per hour. Assuming you’re towing at 65 mph you’d be getting 9.3 mpg. So in order to be in the dark blue you’re working that truck . The dark blue represents 6.2 to 9.8 mpg at 1800 rpm and 65 mph. I would expect when you’re down at that kind of mileage the automatic is going to be selecting 1800 rpm over 1360 rpm. Edit: I didn’t do the math on whether or not you can get a tire size and final drive ratio to do 65 mph at 1800 rpm. If you’re only doing 60 mph at 1800 your fuel economy is going to be about 10% worse to get into the dark blue of the graph. The 1,800 rpm is not the thermal efficiency sweet spot because I call it, it is the sweet spot due to the burn rate of diesel fuel. It is not like it is an opinion that I can change at will. Doing some more research on it, there have been many studies proving this. Of course thermal effiecny of diesel fuel is a little different than the point at where a certain diesel is most efficient due to rev limits and so on. However, most diesels that can rev that high, then 1,800 is generally their sweet spot because of this. Take this slide from a study Caterpillar did for the DOE showing that their C15 engine having much higher thermal efficiency at 1,800 over 1,200 rpm. Peak torque of the C15 is at 1,200 rpm for most if not all applications yet it has a higher thermal efficiency at 1,800 rpm. https://i.postimg.cc/LXjg8Fhj/Cat-TE.png height=500 width=600 Just to tow a combined weight of 21,000 lbs(sometimes 22k) at 65 mph up a slight 1% grade requires 150 hp. Of course this does not account for a lot of wind drag which gets worse the closer I get to the coast. The automatic will try to hold 6th for as long at it can and will for most slight hills, but the boost will be high, fuel pump will be close to max, and my EGTs will be 1-200 F higher than what it would if it were in 5th. My brothers 2012 F350 PSD 3.55 did the same towing his 5ver and he locked out 5th as well. My whole family camps out at the same RV park at the coast and we live within 5 miles of each other so we generally follow each other down when we are towing the RV's. The rear wheel HP required to tow 22k combined up a 1% grade at 65 mph is 38 hp plus the power required to overcome drag and rolling resistance.... So 38 more ho is required on a 1% grade vs level ground. It makes total sense that the EGTs are going to be higher doing the same work at lower rpm.... so what? Are you saying the EGTs are too hot? What kind of fuel economy are you getting in 5th vs 6th? Maybe this is a result of after market tuning?
4x4ord 10/21/20 09:53am Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

^^^^ According to the graph the 6.7 Cummins running in the dark blue is running at 41% efficient.
4x4ord 10/21/20 07:20am Tow Vehicles
RE: Why diesels are most efficient around 1,800 rpm

On the right is the BSFC of the new 2019 standard output Cummins with a higher compression ratio. Its sweet spot is much larger than the 2018 and it would be even more advantageous to tow in 5th at more speeds and loads than 6th if you had a 3.42 axle. https://i.postimg.cc/G2gygv6Y/2018-vs-2019-6-7-BSFC.png height=600 width=800 When that engine is working at 1800 rpm and just up to the dark blue sweet spot as you call it it is putting out a minimum of 150 horsepower. (440 lb ft of torque) According to the graph it would be burning 7 gallons of diesel per hour. Assuming you’re towing at 65 mph you’d be getting 9.3 mpg. So in order to be in the dark blue you’re working that truck . The dark blue represents 6.2 to 9.8 mpg at 1800 rpm and 65 mph. I would expect when you’re down at that kind of mileage the automatic is going to be selecting 1800 rpm over 1360 rpm. Edit: I didn’t do the math on whether or not you can get a tire size and final drive ratio to do 65 mph at 1800 rpm. If you’re only doing 60 mph at 1800 your fuel economy is going to be about 10% worse to get into the dark blue of the graph.
4x4ord 10/21/20 04:14am Tow Vehicles
RE: Junk Food Breakfast Cereals

This thread has made me realize how seldom I have walked through the isles of a grocery store over the past decades. I have no idea what’s available for cereal. About a month ago I started eating breakfast for the first time in about 50 years. I am eating fruit, coffee and or some kind of porridge my wife puts in front of me.
4x4ord 10/21/20 03:24am Around the Campfire
RE: Why diesels are most efficient around 1,800 rpm

There are times it would be advisable to manually shift or lock out gears I’m not arguing that. I am saying that revving an engine higher under light loads with the idea of increasing fuel economy is foolish. No one in their right mind is going to make it a habit of locking out overdrive gears to increase their fuel economy, I never said to revving to 1,800 rpm is a good idea under light load. In fact I said the opposite that under light loads it is best to be at the lowest rpm and higher gear possible. The 1,800 sweet spot only comes into play when you are moderately to heavily loaded, towing something with high wind resistance(like an RV), and/or going up grades. Also, 5th gear is still overdrive on both my Ram and your Ford so you are not taking out all of your overdrive gears, just one of them. I also have 3.42 gears which puts me exactly at 1,800 in 5th at 65 mph while 6th puts me below 1,400 at the same speed. I guess we agree then. When you look at the BSFC map that you posted you can see that the rpm and load you selected are for one very specific circumstance. If you start pulling a little harder the transmission is going to automatically shift down a gear. If you start pulling slightly lighter you will be getting better fuel economy in the higher gear. Towing a trailer down the road is a constantly changing load so the actual load might seldom be at the average. Even if you have a BSFC map for your engine, unless you are constantly watching your instantaneous fuel consumption and are able to calculate in your head how your mpg converts to engine torque and rpm, you will have an impossible task of knowing which gear is most fuel efficient. I'm saying it is best to keep it simple and just let "Drive" with "tow haul" do the thinking for you. The basic principle is throttle down and gear up for better fuel economy. If we find ourselves on a road where the transmission is constantly up shifting only to end up in too high of gear where it needs to recover with a downshift then I know we would agree it's time to lock out 6th.
4x4ord 10/20/20 04:23pm Tow Vehicles
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