Aerodynamics and other factors for mpg
 

Hi guys. Quick preface, last tank I ran stock tuning and recorded a best mpg average for a tank hand calculated of 18 mpg with the 01 in my sig. I decided to try stage one on this crappy hypertech the truck came with to see if mileage was better. I did another trip on the same stretch of highway but this time I had my 16' enclosed trailer for work that isn't even really that heavy say 7K tops?? And I could practically watch the fuel guage go down. It DRANK fuel holding 65 mph on a flat highway. Last time I saw the needle move that fast I was in my v10 truck towing. The average for this tank was a disgusting 10.5. Now I know that I introduced more than one variable in to the equation by changing tuning and picking up the trailer but still? What gives. I am thinking that I need to reduce towing speed more because the cap is causing air to just slam into the front of the trailer. It may be better with the cap off since yo get that swirl effect in the bed that kicks air up and over the trailer. What do you guys think? Is hypertech just crap tuning? What percentage blame lies with aerodynamics? Are the high 3.55 gears that are keeping the engine out of it's efficiency range for towing a contributing factor? I almost think 4.10 would help my mpg in many cases. I didn't expect the full 18 mpg as this tank had some more city but still that is the worst mileage I've ever gotten. Usually around 13-14.

I did fill up again at my destination and removed the tune. Running stock seems to immediately increase mpg for the exact same driving cycle. Like I can drive more miles before I notice the needle start to move off of full. Weird. Guess that's why this tuner is the cheapest and least popular. Does anyone know how their tuning works? It doesn't sound like it gives much timing, which would be a big factor in efficiency. But I'm still curious if anyone has comparisons of towing with cap on and off. I'd like to get some sort of deflector for on top of the cap to direct air over the trailer but it will interfere quire a bit with my ladder rack. Maybe I can figure something out.

A big square trailer, especially at speed and into a head wind, is an effective parachute.

I usually get 12-13 Pulling the Fiver and a 150 HP bass boat. Last trip west I was in a bit of a hurry, didn't have the boat, but bucking a head wind. First time I can remember getting under 10 mpg.

I cant comment on your chip as to whether or not its negatively affecting fuel mileage..... But I would definitely consider it. Try removing it and see what happens. I know power will be horrible but just remember you're collecting important data, not running a race.

As for things which affect fuel mileage. Well above all is aerodynamics. With physics telling us that it takes FOUR times the horsepower to DOUBLE your speed means that the aerodynamic resistance increases exponentially. So you can expect the fuel consumption to react in the same manner.

Point being, lifted trucks sitting higher than stock, larger aggressive tire treads, lots of aftermarket lighting getting in the way, etc... will all affect fuel mileage because they affect aerodynamics. Also if you're driving against the wind then just think of it as driving that much faster. So yes, driving against the windy weather will also result in less fuel mileage.

Obviously in addressing aerodynamics, towing speed is a huge variable. If you want to tug along at 75 mph then you have to understand that your fuel mileage will simply suck. No way around that. But tow more conservative at around 60 and you should see some far more realistic fuel mileage figures.

You can generally tell how much stress and fuel you're using too by what the boost gauge is doing. Boost is a direct byproduct of the fuel being used. So if its hovering around 7-10 psi while towing then you'll probably be getting around 14-15 mpg. But if that gauge is well over 10 psi all the time then you can expect fuel mileage to be more around 8-10 mpg at best.

Actually all that said, the Cummins doesn't seem to care much about how much weight you're towing (to a point). Therefore as long as the object being pulled isnt a massive billboard size shape, you can achieve pretty impressive fuel mileage.

For instance, when I tow a 6k boat which sits low and tight behind the truck, I get great fuel mileage. But when I tow a 7k travel trailer which sits high and obnoxiously flat, my fuel mileage drops by about 6-8 mpg.

I currently tow my 14k 5th wheel which is just a tad smaller than my home and I can get around 10-12 mpg depending on weather, wind, and how many hills I have to go up. I think thats about the norm for these trucks too.

On a side note, you can always try doing things to increase fuel mileage like running 2-stroke fuel, a quality tuner which adds the right amount of timing, run good injectors a tad larger than OEM, and make sure your valves are correctly adjusted. Those few things will help some. :thumbsup:

Thanks for the info. I removed the tuner and went back to stock, before running the same stretch of highway but with the same trailer. Now mind you, I was heading west coming back and so should've had more headwind in my area. Just a crude judge of needle movement, or lack thereof, would suggest the tuner really does a poor job. Time will tell with actual mpg on this tank, but it seems better. I don't think I'll use this tuner anymore and just wait and grab something else later when the tranny is done. Might as well jump on the smarty bandwagon. That or edge comp box. I'm still curious about the hypertech tunes and how they work. Unfortunately I don't have complete guages in this truck yet, they're sitting in the hallway because I haven't gotten around to ordering a pod yet for this truck, but I suspect hypertech just bumps the whole fuel curve higher. Timing advance should result in audible changes that are clearly obvious right? These tunes don't make the truck sound much different.

Unless the box taps into the VP fuel solenoid it doesn't have the capability to add more fuel but rather all the power/torque increase comes from manipulating timing.

Clearly not all boxes are the same either so maybe you Hypertech is just bad mapping or maybe somethings wrong with it. Not sure since I dont know much about those tuners.

NoseCone Pull Trailers

Whoa! That is a dramatic difference. I will surely look into getting one of those cones. Thanks.

That is interesting..... I wonder how effective those nose cones are when you add the variable of a truck ahead of it since generally trailers aren't cruising along by themselves. Another video with a toy truck connected to that toy trailer would be worth making. [laugh]

As for these particular Dodge truck aerodynamics, about 8-10 years ago there was a diesel truck magazine who did an article on making a 1 ton Dodge Cummins 2 wheel drive dually as fuel efficient as possible through aerodynamics. If I remember right they lowered the truck, installed wheel covers like moon caps, took off the engine fan, installed a shell on the bed, etc..... They did everything they could.....and some things which would be completely unrealistic too. But in the end the truck ultimately got somewhere around 30+ mpg. Pretty impressive but no longer a truck you could use for what it was intended for. [coffee]

Call the folks at nose cone and talk to them, every conceivable combination has probably been tested. Trucking companies with 100's of trucks / trailers in there fleet take this very seriously.

Dont get me wrong Colo_River_Ram, as I wasn't trying to insult your input. Very valid points on nose cones but just that the little video made me laugh. [laugh]

Obviously air dams and various items intent on directing air away from turbulent areas of the vehicle are going to help tremendously. Look at the trucking industry and all they go through trying to save a mile or two per gallon. Over millions of miles that adds up for them, but not very logical for the every day family campers pocket book. Although.....I remember back when all this aerodynamics stuff was new technology for the trucking industry, it was claimed that they could make a class 8 semi truck/trailer offer the same coefficient drag as a late 80's Pontiac Firebird. Pretty impressive indeed. :thumbsup:

Great info here. I went to Youtube and watched all the parts. I definitely want to get the nose cone for the trailer, unless the ROI ends up taking years as I may end up moving to a slightly larger trailer within that time. But the discussion makes me wonder how much the 3" leveling kit on the truck reduced aero efficiency. I think the truck looks way better, and it came that way to me, but I wonder if a chin spoiler would make any noticeable improvements. Moving air around the truck instead of underneath. Similar to what is being employed from the factory on the new trucks. I don't get into difficult terrain ever so the reduced approach angle is immaterial to me. Another separate, but equally interesting concept is commercial tuning. I can't recall the thread, but it was on here somewhere where a fellow was remarking on the difference between a cummins with "dodge" tuning and a cummins set up for a commercial chassis application. Apparently, the commercial tuning creates a very small "sweet spot" of increased efficiency while creating compromises outside of that envelope. They mitigate this with use of additional gears to keep you in that 300 rpm envelope (1600-1900). Dodge, being a producer of vehicles that are much less task specific and available to a far wider range of users, opted for a more compromised set up that doesn't perform as well in that narrow band but performs to acceptable levels across a wider rpm range. IIRC the commercial tuning capped rpm at 2600 too. I am intrigued by this specific tuning and I don't think I'd mind a 2600 rpm cap at all as I rarely get there. Provided the truck could do what is needed below that. Which may be hard with the slush-omatic but maybe with a built auto and low stall converter it could stay in that rpm range. Have you guys heard anything about these tuning differences?

No insult taken, we need to be entertained as well as informed and their vids do that. I hope the dude drawing on the truck did not grab a permanent marker by mistake


[coffee]

I've never heard of any different tuning for the ISB but I guess it could be possible since it did come in a wide array of applications. I remember Edge offering a fuel mileage tuner. Maybe checking into what Edge did to achieve any gains would answer some questions. :thumbsup:

From my poor empirical data with enclosed trailers I believe V-nose trailers possible more aerodynamic than ones with nose cones. Had a Wells Cargo 6x7x16 enclosed tag trailer with cap that was replaced by a larger Millennium 8x8x24 V-nose tag and pretty much get the same highway mileage. My last trip to North Texas and back in December I averaged 13.7mpg with the V-nose. Previous towing experiences was anywhere from 10 to 14mpg with the trailer.

So I bet a cap is better than no cap.:thumbsup: