 When the front wheels come...  When the front wheels come off the ground, the steering wheel is nothing more than a handle. Dual master cylinders control cutting brakes that slow the left and right tires individually so the tractor can be directed down the track. |  The Firestone Puller 2000HP...  The Firestone Puller 2000HP tires most competitors use have been tested to wheel speeds in excess of 200 mph! Now you understand why these earthmovers have rollcages. |  John Deere and International...  John Deere and International DT466s are the most popular engines to build for smoker tractors. Figure engines like this put out 1,500-2,500 hp in competition trim. |
Pro Stock is the smoker tractor class that really gets every fan's blood pumping. There are many factors, but the biggest is the 80-foot plume of smoke that is belched from the exhaust stack of these machines. Pro Stocks (in ATPA trim) are allowed a 680ci limit, a single turbo, diesel fuel only, no intercoolers, and the engine can be moved to better balance the tractor. Most tractors are component chassis, meaning that they are tube chassis with a drop in style rearend. Old-style non-tube tractors have a tendency to break in half because stock bellhousings are rated for 145 hp and were being tortured with 2,500 hp. The skinny on these guys is pure overkill. We caught up with one of the biggest names in the Pro Stock class, Lance Little. He and his brother Chris have been national champs and currently run Tantrum Enterprises, one of the premier tractor-building shops in the country. Lance was able to fill us in on some of the finer points of building a Pro Stock tractor. "If the engineers at John Deere knew what we were doing with their engine blocks, they would scratch their heads and wonder how we did it," Little said. These guys are taking blocks rated in the 200hp range and pushing 2,500 horses through them and Lord knows how much torque. "There really has not been a dyno that could measure the torque, but it is astronomical."
Although the tractors resemble their stock brethren, below the sheetmetal, not much remains of the original mechanical assembly. "The block is a John Deere block, but everything else in that motor is billet. We are just making so much power, no stock parts will survive in that environment," Lance said. Would you believe that these tractors use steam technology, too? According to Little, "We're at 1,200-1,250 cc of fuel, and we burn about two or three gallons of fuel on a 10- to 12-second run. We are also using water injection in these tractors, and that does two things. It helps keep the motors from melting because we are making exhaust temps of 1,600-1,900 degrees. And [the] water turns into steam, a lot of steam, and that steam creates a lot of horsepower." One of the most important developments in diesel pulling history was the introduction of billet aluminum and steel cylinder heads about a decade ago. These heads are far stronger and more readily adaptable to the pulling application than the stock heads ever were. "We were blowing stock heads right off of the motors. The heat of the exhaust would make them crack, and we were just breaking them left and right. The billet stuff has allowed us to make so much horsepower because we can modify them and try new things. Our head flows 475-500 cfm, and we run a (roughly) 2-1/2-inch-diameter intake valve."
To get all of this power to the ground, a Crower-glide four-disc slider clutch is employed. This sounds familiar to you drag racing fans out there because it is the same style of clutch used in many ultra-high-horsepower drag racing applications, but unlike drag racers, once the clutch is tuned it stays where it is for most, if not all, of the season. Little said, "We start out with the clutch set to 0.085 or 0.090 of an inch, and by the end of the season we are around 0.120 of an inch. That clutch sends the power to a Pro-Fab transmission. Those guys build transmissions for all of the high-powered pulling classes." Finishing off the drivetrain, a stock rearend housing is highly modified to accept an Eaton rearend center section and differential from a semi-tractor. Little currently runs a 3.90 gear ratio to make the wheel speed needed to pull the sled.
But, the whole sled-pulling program comes together with the right turbo. The Pro Stock class has no restrictions on turbo size, so you won't be surprised to know that Little said he runs a 5-inch exhaust wheel and a 5-inch compressor wheel. Yikes!