GMC Duramax Diesel Racer - Really Truckin'
Duramax-Powered Road Course Racer
Gale Banks could have invented that familiar expression about thinking outside of the box. Long known for developing a number of innovative high-performance projects, his latest endeavor is not just a hot ride but a whole new approach to diesel performance. Banks is out to prove to the road-racing world that a 6.6L Duramax diesel can rev up like a gasoline engine and best the competition.
"I'm taking all of my years of gasoline performance and applying it to a diesel engine to make it more gas-like," he explains. "We got rid of some of that diesel torque and lost some of the weight, because we like it to spin faster." And in the process, he created a whole new breed of engine. Think of Banks' truck as crossbreeding between a sturdy Clydesdale and a thoroughbred racehorse.
It's easier said than done, of course, but keep in mind that the Duramax engine is very robust, so it has plenty of oats to spare. "The durability of this thing is unbelievable," Banks says. "We've tuned it to death and haven't hurt it."
Let's take a look at just how much power he's squeezing out of a Duramax. Normally, a stock LLY block calibrated with a manual transmission cranks out 310 hp at 3,000 rpm and 605 lb-ft at 1,600 rpm. Now, imagine it revving up to as much as 5,000 rpm-nearly 2,000 rpm above redline. Depending on the tuning, Banks' dyno figures show outputs of 650 to 700 hp and 800 to 900 lb-ft of torque. Note that the horsepower more than doubles, while the torque increase is about a 50 percent gain (we'll explain why in a moment). More torque could be dialed in, but the Banks team has to make sure the rest of the drivetrain will survive this flood of power. What a concept-and one that requires digging into some serious tech details.
Before getting into that, however, let's cut to the juicy part. Gale Banks wasn't just planning on printing out dyno sheets. Instead, he hitched this spotted pony engine program to a tube chassis GMC Sierra race truck and created the Sidewinder D-Max Type-R. The "R" refers to the fact that it's been heavily modified for road course racing.
The plan is to have the truck compete at the 2006 National Auto Sport Association series in the Super Unlimited Class, which can include World Challenge and other high-end road-racing cars. Other endurance events are in the works, as well. (Lest you think it's odd for a diesel to compete in an endurance event, look no further than the Audi R10 TDI that just won the 12-hour race at Sebring.)
Getting a truck to run hard and long in a road course race required a massive amount of development to build the NASCAR-style chassis and fabricating the aerodynamically enhanced body panels.
Starting with the frame, it was fabricated from a combination of mild steel and chrome-moly tubing. Rules don't restrict engine placement, so the Duramax was located 18 inches back and 16 inches lower than stock to achieve a 50/50 front to rear weight balance. For an improved power-to-weight ratio and handling agility, the overall vehicle weight was kept to 3,200 pounds.
Working in conjunction with crew chief Sheldon Tackett, driver Don Alexander, who manned the wheel for the Banks' land speed record in the Cummins-powered Dakota, designed the front and rear suspension geometry. Custom front A-arms and spindles were fabricated at Banks and mounted along with Koni shocks and Eibach springs, which control the rear three-link. Massive 13-inch Wilwood brakes put the bite on the Bogart wheels, shod with Goodyear Eagle racing rubber-Fronts are 25.5x12-17 and the rears are 28.5x14.5-17. These Le Mans prototype tires are available in soft, intermediate, and hard endurance compounds to meet varying traction and tire-wear conditions.
Knowing that tons of torque is on tap, Banks is experimenting with a four-disc carbon/carbon clutch assembly in a Tilton magnesium bellhousing. The rest of the driveline is equally stout. The gearbox is a four-speed clutchless unit linked to a Speedway Engineering Track-Nine 9-inch Ford-style rearend with a Detroit limited-slip differential.
As for the body panels, although loosely based on the GMC Sierra, they were heavily massaged and remade in composite material by Banks' stylist Sean Torres, all with an eye for less wind resistance and improved performance. The latter aspect required designing special vents and ducting to ram air to the turbos and for engine and brake cooling, along with shrouding around the tires and rocker panels to take advantage of ground effects. The Type-R was also outfitted with a rear aeropan to better manage airflow exiting underneath the rear of the truck.
Getting back to that unusual engine configuration, what does it take to nearly double the operating speed of a diesel? Beginning with the fundamentals, Banks explains that, "Most gas engines have a 1:1 torque to horsepower ratio, while diesels make torque at 2:1 ratio over horsepower. The main thing is to maintain the torque advantage but get rid of the current weight. My goal is to shift the ratio to 1.5:1." In other words, keep a 50 percent torque advantage over a gas engine. This stated performance goal also helps to explain, in part, why the horsepower figures increased so much more over stock than the torque numbers, as noted before.
To find out how Banks engineers skewed the ratio, let's work from the top down. They designed custom intake manifolds that feed air into the carefully massaged ports of the cylinder heads. Flow testing produced data that helped to increase intake port flow by more than 30 percent at 0.500 lift, and exhaust port flow by a whopping 50 percent at 0.500 lift.
In the company's typically meticulous fashion, Banks engineers experimented with four different cylinder heads, in order to achieve a fine balancing act between flow versus swirl. "Everything you think you know about porting a gasoline cylinder doesn't necessarily apply to a diesel," points out Banks Power's engine builder Dave Basham.
Some of the alterations included custom stainless steel intake and larger-diameter Inconel exhaust valves to replace the stock intake and exhaust valves. Both valves are now 33mm (stock exhaust valves are 31mm).
In addition, custom Manganese bronze self-lubricating valve guides and tungsten carbide alloy valve seats were used to conduct as much heat away from the surface of the valves as possible. To reduce valvetrain mass, smaller, lighter, and shorter cam lifters were developed to travel in bronze guide bushings pressed into the Duramax block.
Other measures are required to keep this engine from tearing itself apart. That's because the twin Garrett Le Mans-style racing turbochargers generate enormous boost pressure in the neighborhood of 44 pounds. Of course, this much pressure requires special means for sealing the heads to the block. Garlock Helicoflex low-distortion sealing rings are being tested, and Banks-spec custom studs will also replace the stock head bolts.
Banks-designed custom tube headers, fabricated from stainless steel, channel exhaust gases to the dual turbos, and electronically controlled Banks-designed dual wastegates have been built. A pair of large air-to-air intercoolers will be used to reduce inlet air temperature to provide maximum air density.
Obviously, with this much airflow you need way more fuel, not merely in quantity but also in quality. Bosch created a higher-capacity fuel system and matching engine management package, with custom programming handled by Banks engineers. Included are special fuel injectors with modified spray angles and flow ratings, as well as a higher-volume injection pump built to Banks' project specifications. The Bosch fuel delivery system is capable of providing adequate fuel (at 26,106 psi) for a turbodiesel engine producing as much as 750 hp and 950 lb-ft.
The upgrades don't stop there. Inside the block, the 14.5:1 forged pistons have custom 4340 billet-steel H-beam connecting rods with lightweight tool steel piston pins. Interestingly, the combustion chamber is in the piston head in order to facilitate the swirl mentioned above, which in turn reduces smoke. A special flow bench that measures swirl was used to design the proper piston shape.
To further reduce the heft of the rotating mass and its resistance, the crankshaft was lightened, knife-edged, and contoured. To handle the increase loads, it was also shot-peened and stress-relieved in a cryogenic bath at -300 degrees Fahrenheit.
For additional strength, Banks custom-machined a billet aluminum dry-sump oil pan that also serves as a block reinforcement girdle. The new oil pan is shallow enough to permit the engine to be mounted extremely low in the chassis.
The hard parts were not the only challenges. Tuning the fuel injection for smokeless performance required countless hours of laptop time. The engineers can't just pour buckets of fuel into the cylinders at will and then blow out all kinds of sooty exhaust. Black smoke will lead to a black flag from race officials. "Smoke is the negative legacy of diesel-it's just plain wrong," Banks points out. "It's power you can see but not use."
Suffice it to say, a project vehicle of this scope and audacity has many more technical aspects than can be covered here. What's even more amazing is that the Sidewinder D-Max Type-R is just the first of many more diesel performance machines in the works.