Vortec Vs. Duramax for Gas Mileage

The Duramax has come in a number of different variations. The 2001 to 2004 LB7 was a 6.6-liter V-8 producing 300 horsepower, and the 2004 to 2007 LLY produced between 250 and 305 horsepower. A variant of the LLY known as the LBZ -- 2006 and 2007 -- produced 360 horsepower, but improvements kept it as efficient as the standard LLY. Later LMM variants produced as much as 400 horsepower, but retained the less-powerful engines' 6.6-liter displacement and efficiency.

Vortec engines have been around since the 1990s and have come in all GM trucks produced since then, but only a handful of Vortec-labeled engines came in the same chassis as 2001-later Duramax diesels. The Vortec 4300 (code name LU3) was a V6 based on the original small block, and produced 180 horsepower. The Vortec 4800 LR4 V-8 produced 270 to 290 horsepower, and the 2007-later 4800, coded LY2 produced upwards of 302 horsepower. The Vortec 5300 from 1999 to 2007, LM7 model produced between 270 and 305 horsepower, and the L33 Vortec 5300 produced 330 horses. The 315 horsepower LY5 replaced the LM7 in 2007, Vortec 6000 and 6600 engines are the largest and most powerful, producing around 400 horsepower depending on the application.

Diesels are, by nature, more sensitive to driving conditions and driving style than gas engines. In the city, LB7 drivers can expect 17 to 18 mpg, though figures might vary as low as 15 or higher than 20 mpg depending on your driving style. Highway figures may come in as low as 17 mpg, but land between 19 and 21 mpg at interstate speeds.

Expect between 15 and 16 mpg in the city for your LLY or LBZ-equipped truck. Mileage should range between 17 and 20 mpg on the interstate, but could dip down to 15 to 16 mpg depending on your particular truck. The LMM tends to achieve about the same fuel economy as LLY and LB7 engines.

In the Silverado 1500 pickup, a Vortec 4300 will return 15 city and 20 highway mpg with an automatic, one mpg less for both with a manual transmission. Vortec 4800 trucks return an identical 14 city and 19 highway mpg with a manual, one less mpg highway with an auto. The Vortec 5300 will net you about 14 mpg city and 18 highway miles. Heaver SUVs return about one mpg less per gallon across the board. Vortec 6000 and 6200-equipped SUVs like the Cadillac Escalade and Chevy Tahoe will net about 12 mpg city and 19 on the highway.