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!