20.5 mpg Dodge RAM ABA testing run

[JRMichler]

Originally Posted by slowmover

So, while it's always a pleasure to see a guy get 20-mpg in a pickemup (an impossibility in the years I was growing up, it still astounds me) and I pass along my congratulations to you, I'd be mighty careful about gearing/tire-height/load capacity changes.

I once had a 1955 Ford 1/2 ton six cylinder that would get 20 MPG. The king pins were worn so bad that it could not be driven over 50 MPH and the engine was so loose that it rattled until the oil pressure came up.

I also had a mid 70's Ford 1/2 ton that got 20 MPG. That one had a small block V8 and three on the tree. I wondered why the engine rattled until I dropped the pan and found a handfull of piston skirts laying in the sludge. I assume that losing half of each piston had something to do with reducing friction, which would at least partly explain the good mileage.

[ECONORAM]

OUCH!! I guess that might help...lower piston weight.
The Dodge 4.7L is supposed to be a sludge engine, but when I pulled the valve covers off, everything was clean as a whistle (whew). No extra parts either! I am a little anal, as I've only run synthetic oil in it since 1500 miles, and I keep a FilterMag on the oil filter.

Thanks for the kudos. It has taken me a few years to get to this point. I was not convinced aerodynamics really helped until I moved back to North Texas from northern Utah. There I could get 24 mpg on I-80 from Salt Lake to Wendover. But the air is thinner at 5,000 feet. Once I realized the drag reduction was a key element, I got really serious about researching drag and reducing it. Ecomodder has been a great site for learning!

@Blu3Z3rg, I heard it will help Dodges to get rid of the OEM muffler. Guess I'll find out soon enough, as I bought a couple 3" pieces from AutoZone to replace my muffler with. Wonder if the wife will notice?

[edit] It's 4 hours later, straight pipe installed, muffler removed. WOW, is it LOUD! That small resonator after the muffler seems to do nothing. I guess I'll be putting the muffler back on... Glad I didn't damage anything during removal.

[edit 2] Oh was that loud! Around town it was not too bad. It did have a nice loud crackle when I cranked it up for cold starts. On the highway, as long as I was at 60 mph or less it was okay. Above that and the resonation in the cab was not tolerable for me. I had to turn up the radio just to hear it. OEM muffler is back on now, until I can figure out what high-flow muffler combo will keep it quiet enough to maintain my hearing.

[ECONORAM]

Sigh, I guess I should have just stayed home tonight. I went out, despite seeing we had 12 mph winds, to do some ABA testing. Non-starter. I did learn 2 things: 1) if I can't keep the vacuum gauge above 7" Hg for any length of time on a flat stretch of road (there's one about 12 miles away, on the way to my test road), it's time to park the truck and wait. 2) while driving to the test road, I had the 12 mph tailwind and noticed my truck getting mid-20s for mpg. I then surmised if I can figure out the drag at that speed, minus the wind, and then use ratios to compare with my drag and mpg at 0 wind speed, I should be able to compute what I need my drag coefficient to drop down to in order to achieve the fabled 25 mpg @ 65 mph. It's a shame :banghead: I had to burn :banghead: over 5 gallons :banghead: of premium :banghead: to figure this out. I've not figured out what the FE was tonight, but after the return trip where a panel came loose, I'm not sure I care. Guess I'll wait another couple weeks for better weather.

[ECONORAM]

Originally Posted by brucepick

Good on all the work you've done so far. With EPA Highway of 17 and you're getting 20.5 approx, that's a really good improvement - more than 20% above EPA already.


I think aero mods are definitely going to help you. I'm guessing that in Texas you do lots of highway miles, 60 mph and above. I got a lot of benefit from my belly pan on the Civic, and most of that benefit seemed to come from the front section between bumper and firewall. The planned wheel covers are a good idea.

Think about a tapered cap, one that gets shorter at the rear. I saw some discussions and pics of those in the Aerodynamics subforum. Should be pretty easy to build one that actually helps your aerodynamics. If you want to make it look cool or macho, you'll need to tackle that separately.

Oh yeah - tires. If yours are knobby off road capable ones, consider tires with a smoother highway tread. And in any case, air them up to the max imprinted on the sidewall. And check pressure often.

Mostly we find that better flowing intake and exhaust don't help fuel economy a whole lot. They improve the max power output you can achieve, if the original provided some restriction. Remember, you're likely only using a tiny percentage of the engine's available power. At the low throttle levels used in hypermiling, the amounts of air in and exhaust out are far below the capacity of even a bone stock system - in my humble opinion, of course. Three inch pipes can help at wide open throttle at max rpm. You're likely at 1/3 throttle and 1/3 max rpm most of the time, so 1/3 * 1/3 = 1/9 of max/max air and gas flow. Am I close in my guess?

Yes! In fact, I noticed that my engine is only showing like 12-14% throttle opening when going down the highway; that was a real eye-opener.

I do want a tapered cap but the spousal unit likes the one we have now (stnd Leer type).

I did a new aero mod this weekend, which seemed to help. I put some fairings in front of the rear wheels, as I have done with the front wheels. I have not been able to test this ABA style yet, but on my trip back from OKC Sunday the truck got 20mpg into a 12-20mph headwind, while I was traveling @63mph. I've never gotten that good FE into that much wind before. Now, it was 90* out, and I would not use cruise much, and did let the truck slow down to about 58mph up most hills. I plan to rig up something to help me maintain a 90* air stream into the intake, and ABA test that as well as the new fairings. Any ideas on the hot air intake? I tried one briefly, but my exhaust manifolds have an exhaust wrap on them and I didn't see any intake air temperature difference...

Originally Posted by mcrews

good job!!!
trucks are tough.
Think about going up a size on the tires (ex 245 to 255) when you go to buy them again. as brucepick said, it's about lowering the rpm on the road

I am actually considering some 255/55R20s; a little shorter and a little narrower. My truck's tires are 33" tall (275/60R20) and wide, and give me an effective 3.55 rear end...which is pretty tall for my 4.7L. These would bring my gearing to about 3.78 and would be nearly an inch narrower each. Plus less rotating weight...
But that is only after these tires wear out. 46K and they still look good!

[ECONORAM]

An update on my continuing wheel cover saga. I have tried using 2" clear packing tape, 4mm corroplast, and LEXAN in 0.100" and 0.015" thicknesses for covers. I've tried to secure them to the wheels with doubled up tape, double-sided tape, adhesive backed velcro, 550 cord, white string, zip ties, ==>and soon double-sided velcro straps. Clear tape worked fine aerodynamically, but it did not do well in 30*F temps. I then tried black 4mm corroplast first with double-sided tape and then tied on with 550 (parachute) cord. Tape doesn't work--Period. Front covers would depart the vehicle upon reaching 65mph. 550 cord worked well, but the corroplast didn't look that great. Not even when I painted them silver. I flipped the painted side against the wheels and left the unpainted black outside. That looked a little better. It was also a little tough to run the cords through the holes, and I had to use pliers to pull the knots tight.
Special NOTE: It is only NOW I start using 2 inch (or so) pieces of foam weather-stripping stuck to the wheel covers so the foam rubs against the wheels and doesn't scar up the paint anymore. I place it between the holes where I run the 550 cord thru the covers. The wheel spokes aren't so pretty after getting rubbed on by painted corroplast for 4K miles.
Next up was LEXAN. I wanted 0.125", but the shop only had 0.100" Turns out #1 even 0.100" LEXAN is heavy and #2 when I cut them into 20.5" disks for my 20" wheels, that left a little too much room for flopping up and down as the truck rolled down the street. So much I'll have to touch up the clear paint on the rims damaged by the covers. To compound matters the cover flopping was actually causing a wheel balance problem on the highway. It did not matter that I used pliers to tighten the 550 cord; the covers were so heavy they'd work the knots loose. One trip from OKC to Wichita Falls, at 70 mph the truck was averaging 20mpg...but I had to take the covers off because of the vibration. To still maintain 20mpg, I could only drive 65mph. That was proof positive to me the wheel covers were beneficial.
Next I ordered some 0.015" LEXAN. Figured I'd drop some of the cover weight and still keep the see-through look. I first tried double-sided tape but it still didn't work. I should have used 550 cord and pliers again, but I elected to use white nylon string. Mistake. The aero forces on the covers are enough to work the knots loose, causing the covers to flop around and eventually catch air...and depart the vehicle. I ended up loosing the front two covers somewhere between here and Fort Worth because they tore right through the strings. Good news on that trip: before the front covers departed the truck I was getting over 21mpg on the tank--no wind that day (rare here in north Texas) and I was traveling 65-67 mph.
So now I am using 14" nylon zip-ties to secure the 0.100" LEXAN covers. I was afraid to use zip-ties initially because I did not want them rubbing through the paint on the wheels. But with the previous experiments I've done and how torn up my wheel paint is I think that's a moot point now. The good thing about the zip-ties is I can get them tight, and they hold the 0.100" LEXAN covers but good!! Using the foam weatherstripping here helps, as you can see it compress as you pull the zip-tie tight.
Next on the list is to cut another set of 0.015" LEXAN covers but at 20.75" diameter. 0.015" LEXAN is thin enough to cut with scissors--the 0.100" I had to cut with a Rotozip. The inner diameter of my wheels where the wheel weights get clamped on is 21", but I cut the last ones to 21" and had some trouble getting them to stay flush against the wheel. Now I'm really glad I ordered enough 0.015" LEXAN for two sets! I recently ordered some 3/4" double-sided velcro to secure the covers to the wheels. Fuzzy side in to protect the wheel paint on the spokes, sticky side out, overlapped on the outside of the wheel cover to secure.
The intent is to find a secure method to keep the covers on without marring up the paint or requiring modifying the wheels in any manner.

[ECONORAM]

Another wheel cover update. Cut the 0.015" LEXAN to 20.5-20.6" diameter and used some velcro on the rear wheels (ran out of velcro) and used nylon tie-wraps on the front. Still couldn't get them to stay flush. Even tried using double-sided tape to glue it down. The zip-ties starting tearing through the covers as we drove down the road. A 20-mph headwind probably didn't help, but it is apparent the forces on the front wheels are stronger and more varied than on the rear wheels. Looks like I'll be going back to the 0.100" covers for the meantime, with velcro or zip-ties to secure. I might try some .040" in the future... That said, the corroplast worked just as well, but you can't see the wheels.

[t vago]

I've bought a set of Impostor Wheel Skins for my truck's wheels, along with a set of aluminum pizza pans. I prepared the outer edges of the pans and the wheel skins, then bonded them to each other using urethane windshield RTV. As an added safety precaution, I also used zip ties through 5 sets of holes near where the wheel skins and covers were bonded to each other, spaced equally among the circumference of the wheel skins. They attach pretty easily to the wheels, and take a fair amount of prying to remove.

Wheel skins: Impostor Wheel Skins

They've held up for nearly a month now, with no noticeable looseness or imbalance.

[ECONORAM]

Vago, those covers look like a good idea. If the pizza pans stay you have it made!
In other news, my truck went through a hailstorm last Monday and broke 2 blades on one of my front mounted radiator fans. Vibration was so bad even with it windmilling that I had to remove it. So, this weekend I installed a used Taurus 3.8L e-fan. Learned the hard way I wired it backwards, so it was pushing warm air out the front inside of pulling it through the radiator. Got it rewired and on low speed, it works very well. Keeps temperatures more stable than the previous fans, and nearly as good as the clutch fan. Haven't wired up the high speed part yet, but figure I can get to that before I start towing later this summer...
Turns out one or two of my wheels are out of balance, not the fault of the 0.100" LEXAN covers.

[ECONORAM]

I've not forgotten to mod; just been pretty busy. Moved this summer to a new job in San Antonio. Bought a house and had to clean it up good (previous owner had cats...LOTS of furballs remained). I'm getting the truck ready for a road trip and here's what I've done:
Added third belly panel that extends coverage to the rear axle. Replaced front fwd wheel fairings smith better pieces. Replaced rear wheel fwd fairings with better pieces (one old one flew off on the interstate...). Installed the 0.015" LEXAN covers on all four wheels with velcro. Briefly tested today at 60mph and so far so good. Hoping to see low to mid-20s this trip, despite the terrain.

[ECONORAM]

Originally Posted by Blu3Z3rg

I just converted to a straight pipe... i'll let ya know!

And YOU let me know about them cams!!!!

I'm looking to do underbelly pans as well, do you think this is where your most significant change is? And 3" on the intake is plenty large, 2 3/4" is what I calculated to be ideal for a 2500 power peak from flow. I won't say it has made or broke the mpgs, but I'm not going to redo it. I just have a shield I can put on or take off for the varying temps.

The problem with trucks is the weight and the huge front area, which is why letting the piston speed go a bit faster is better for trucks.

HO cams. As for MPG, I think I lose a small amount. At least when I was puttering around the air base and in town. On I-44 however, things were different. It was obvious the truck was making more power. It did not downshift when I set the cruise and left it. Can't remember if it was at 65 or 70 mph, but I know pre-HO cams install, the tranny would downshift several times at that speed with the cruise set. Will I go back to the OEMs? No way. These are way too rewarding.

Belly panel kit. I do think this is a big area for mpg gains. This, some splitters or fairings in front of all four wheels, and blocking part of the front grill. These and the wheel covers also help things along.
--that said, the belly panel kit is about to undergo a major renovation. I did my 20.5 mpg runs with a hand-cut piece under the engine bay that barely allowed me to make normal city turns; it was so close to where the tires and wheels turned into. When I tore it up going through a huge rain puddle, I had to revert to my old 4' wide Al sheet, which left a lot of the front suspension and wheel wells hanging out in the breeze. I did have the areas covered between the frame rails and the body, which are big air catchers. I also noticed the panels were about as smooth as the Black Hills of South Dakota; didn't know I was so sloppy. Despite these shortcomings, we did manage a tank at 21.4 mpg from Oklahoma City to San Antonio this month. Nearly 450 miles with not quite a quarter tank left.
My lessons learned: #1. panels need to overlap a couple inches, end to end, so the front of one doesn't get sucked into the airstream. #2. the cleaner you make the front, the better off you are. Cover as much as you can. (I let the front wheels abrade the corroplast so I could trim it a bit at a time.) #3. Make it smooth. Look at the bottom of an F1 race car; nearly seemless and flat. #4. Make your mount brackets accessible. One of mine can only be reached from the driveshaft, not the framerail...which is a real hassle. #5. mount your panels from the inside out. I run 4' wide panels down the middle, then add the sides. #6. Make the panels removable. I can remove nearly the entire kit in an hour. #7. Use L channel for most of your brackets. Why? Flat metal strips don't offer enough rigidity to keep the panels flush. #8. Beware of what factory bolts you loosen to install stuff. I loosened two that blew my alignment and didn't know it for some time. #9. If she who must be obeyed gripes about the truck's appearance 'cuz of all the stuff you strap to it, keep going.

Wheel covers. UPDATE. I am using 3/4" wide velcro strips (thanks Ebay) to hold the 0.015" thick covers on all 4 wheels. Worked great on the above road trip. Didn't lose any, didn't tear any. I have learned not to cinch them down super tight; leaving a little slack lets them stay near perfectly flush. Brake dust does accumulate on the wheels though.

Tire fairings. Big item. I fashioned some wedge shaped fairings to mount in front of each tire. My truck has 275/60R20s; 11 inches wide, that is a LOT of tire. These definitely cut the drag...don't change my S (frontal area) 'cuz they are just as wide as the tires; maybe a couple mm more. Mine hang down about 8.5 inches from the front spoiler lip. I do need to take care in steep entrances, and avoid getting close to parking blocks.

Frontal area. In time, I plan to fabricate a slope nose (a Daytona nose for you old MOPAR fans) to block the entire front grill, and open the narrow slot in the center of my bumper. That should still give the radiator enough airflow, yet reduce the truck's parasitic drag.

Wheel balance. Not sure it affects MPG, but it does make things smoother. 51K on the tires now, and 3 of 4 wheels were out of balance. I could tell because of the dirt spots left from the old wheel weights...

Intake. I agree with you there. I still have my 3.5" steel mandrel bent pipe, but anticipate I'll soon change it to a 3" PVC pipe. PVC is quieter. Since it's 3" inside diameter, that is pretty close to what my throttle valve is (68.5mm). Future plans include repositioning the filter box right behind the radiator, getting a direct feed from it, and then straight into the throttle valve. Coming through the radiator is worth about a 5* temp rise.

Hope to make some test runs later this week. Found a good 1.1 mile stretch of flat road I can use. And it's not too far from home!