Shag

What 4wd gets the best mpg?

33 posts in this topic

I need to replace our 2000 Pathfinder, which was my wife's car for the beach but is now our around town car. I have a diesel F350 but it is a lot of truck to go on the daily run and a lot to air down and up. It doesn't have to

be newish, just not someone else's beach truck, hopefully better mpg and much shorter air ups. 

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If price is no option, the new Colorado/Canyon diesel, almost 30 highway, 20 city.  

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We've got a all wheel drive 2014 Sub Forester, thing gets like 32 mpg. And it has some pep!

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has anybody seen this ? ..... imagine getting 37 mpg from a full size truck ? :eek:

 

We've been covering Achates Power's highly unusual inline-three-cylinder two-stroke engine with six pistons and two crankshafts for some time now, and it's finally installed in a Ford F-150 truck for demonstration and fine tuning. The stats are pretty impressive if they prove reliable in production trim: 270 hp, 480 lb-ft, and 37 mpg combined fuel economy. The test engine is running 18.5:1 compression with direct gasoline injection. The long stroke of this 2.7-liter engine allows the pistons to extract maximum work, and because there are no cylinder heads (intake and exhaust flows through ports in the cylinder walls that get exposed at the extremes of the piston travel), there's far less heat rejection to the cooling system. Achates says this helps deliver thermal efficiency of near 50 percent—and that's before any in-vehicle thermal-management optimization work.

The current design features a single large-diameter gear connecting the upper and lower crankshafts. Interestingly, the two cranks don't do equal work. The one on the side exposing the exhaust ports transmits about 60 percent of the torque while the one with the pistons that expose the intake ports bears 40 percent. The engine is twin-charged, with a supercharger (needed to move sufficient air at startup and low speeds) and a turbo. They operate at low levels of boost, so less air flows through this engine than is typical for a four-stroke diesel. This helps keep the exhaust temperatures in a narrower range—the lowest operating exhaust temperatures are higher, and the highs are lower than in "normal" engines. This makes life easier for the exhaust after-treatment system, which will likely include a lean-NOx trap. The engine produces sufficient heat to warm the cabin, but the required radiator capacity should be less than in a traditional truck.

The Delphi direct-injection system features two injectors per cylinder operating at about 22,000 psi on gasoline (36,000 if running diesel, which reportedly increases the combined economy to 42 mpg). They spray directly at each other, with combustion initiating in the center of the cylinder, so the cylinder walls never get sprayed by fuel. Achates claims there has also been no issue with oil finding its way out of the intake or exhaust ports because the oil control rings remain below the ports. At least one (as yet undisclosed) manufacturer has plans to build the engine, and several more have expressed interest. Stay tuned, as this promises to be the most radically reimagined engine to power a passenger vehicle since the Wankel rotary.

 

 

BBIwSel.jpg

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6 hours ago, ne_dan said:

If price is no option, the new Colorado/Canyon diesel, almost 30 highway, 20 city.  

 

 

Yep'

 

Amazing... but pricey as hell 

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The Achates engine is being developed with Army money, initially as a replacement for a particular, much-used Cummins engine - I forget which one. The description of the valves, as replaced by holes in the cylinder wall, sounds like the designers have stolen an idea from sleeve-valve engine design, which was widely used in the UK and Europe through WW II and a bit thereafter.  Opposed-cylinder engines have a long history, too. Many US subs in WW II were powered by opposed-cylinder engines from Fairbanks Morse, and those engines were carried as an emergency go-home power by nuclear subs until quite recently. 

 

I'll venture a WAG that the engines' lifetime will be much less then a traditional diesel with poppet valves, but the tradeoffs in power/weight ratios may be well worth it in some applications.  If it works in this engine, you can anticipate progressively bigger engines coming along, too.

 

Betcha the proposed manufacturer is Cummins. 

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13 hours ago, ne_dan said:

If price is no option, the new Colorado/Canyon diesel, almost 30 highway, 20 city.  

My GMC Canyon 6cyl gas gets 25 hway 19 around town

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13 hours ago, BrianBM said:

 ...................sleeve-valve engine design, which was widely used in the UK and Europe through WW II and a bit thereafter...................

 

.................Opposed-cylinder engines have a long history, too. Many US subs in WW II were powered by opposed-cylinder engines from Fairbanks Morse,.............. 

 

 

Sleeve valve engine were also used by Willys in the Willys Knight  here in US. The F-M opposed cylinder engine was the prime mover in a line of locomotives built by them such as the Trainmaster.

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Aha!  

 

AFAIK no one is building classic sleeve valve engines anymore. The poppet valve, in one form or another, reigns supreme. Am I correct in that?  

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Posted (edited)

I guess I should have worded this better. Not looking for a new vehicle nor even new technology. Looking for the best mpg for the used buck. Years ago the old Troopers with a 4 cylinder stick were getting about 24 hywy with mega room for storage. Looking for a similar     outcome. A friend suggested a Honda Element with 4 wd, but I think it's really AWD and I'm not convinced AWD would fit where I go clearance wise as well. Keep the suggestions coming. I thought Subaru's just came with  those Coexist bumper stickers. Like Rams come with rubber testicles.

Edited by Shag

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