https://ecomodder.com/forum/member-a...mendations.jpgI looked back at the 2002, Popular Science Magazine's mpg shootout, between a Ford sedan and Chevy Silverado LS 2500 Crew Cab, with 6.6-liter turbodiesel V-8, 2,667- kg curb weight, at 55-mph test speed.
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Internal GM memorandum placed this pickup at 17- mpg highway, @ 55-mph.
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GM's mpg guru, Roger Clark, recommended five aero-mods:
1) upper grille-block
2) upper fascia grille-block
3) lower fascia grille-block
4) underbody, inter-wheel, body-to-frame gap- sealing
5) and a full tonneau cover over the bed
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@ 55-mph ( 88.5km/h ) these five aero-mods increased constant-speed cruising fuel economy to 26.0-mpg ( 9.064-liters/ 100 km ), a 52.9% improvement.
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The thermal efficiency of your gasoline-powered RAM is less than a turbo-Diesel, and Diesel fuel itself has more energy density than gasoline, so your absolute mpg numbers would fall accordingly, but 12-L/100km/h is only 19.61 mpg ( at US Gallons-equivalency ), and I've seen as high as 39.9 mpg @ 65-mph ( 104 km/h ), compared to 25.14 OEM, with my gasoline-powered Toyota, so the 12-liter target seems very 'achievable.'
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And the 'faster' you drive, the more important aero becomes, as the power to overcome it is increasing with the 'cube' of the velocity, whereas, the drag is only increasing with the 'square.'
EXAMPLE:
@ 65-mph, your aero hp is associated with 65- cubed ( 65 X 65 X 65 ) =274,625.
@ 75-mph, you're at 75-cubed , or 421,875.
Performing the ratio, whatever your aero horsepower requirement was at 65-mph, at 75-mph it's now 153.61% of what it was, with just a 10-mph velocity increase ( 53.6% ), while your rolling-resistance power requirement has only risen by 15.3%.
Speed costs!