During its first race season, our goal was to get into the 12s, which was accomplished with a best run of 12.8 seconds at 111 mph. Now that the season's over, we'll work on a few chassis refinements and plan to significantly improve performance by next season. At more than 1000 pounds lighter than a stripped-down heavy-duty 2WD 3/4-ton GM diesel pickup, our street-legal and air-conditioned 4x4 hot rod definitely has an advantage.
While a highly modified big-block gas engine might produce 12-second performance in a similar truck, it also loses much of its streetability and gets abysmal fuel economy. Our Duramax hot rod will produce nearly 25 mpg cruising at 75 to 80 mph on the Interstate, with road manners that return to normal by switching off the extra power.
We drove the truck through the summer with the original 3.42:1 differential gearing, but considered installing 3.73s to match those used by GM's new diesel pickups. However, after discovering the ease at which it cruised at speed on the highway (while getting excellent fuel economy) and how it performed at the track, we decided to keep the 3.42:1 gearing. Someone with the willpower to drive at a more sedate speed could probably get even better fuel economy by another two or three mpg.
The Allison is arguably the toughest automatic transmission offered in a light-duty truck to date, but there's a limit to how much torque it can handle. Designed to live behind a factory Duramax 6600 (rated at 615 pound-feet of torque as of January 2005), the Allison torque limit will be exceeded with some of the higher-rated aftermarket power products in a conventional 3/4- or one-ton truck. However, Allison engineers and diesel race enthusiasts have suggested that this lightweight hot rod could likely "squirt" out from under the factory Allison torque limit. We've yet to slip the Allison during a clean launch, but we're watching a number of companies that offer performance transmission upgrades, should the need arise.
This has been a fun project that'll see continued development and may even appear at a couple of the larger diesel-pickup events during the upcoming season. Keep your eyes open at any number of diesel drag races around the country. You may see us there.