Diesel Drag Racing, Stage II

Nov 24, 2009

Diesel drag racing offers some of the biggest motorsports fun available. Businesses who sell traditional speed parts for cars might not know how competitive a late-model diesel pickup can be at the track on Friday night by adding a few off-the-shelf parts. Even better, no tow vehicle and are trailer required.

This time, we’ll cover ways that diesel shops and parts retailers can help enthusiasts get in the 12s or even the 11s while keeping their trucks street-legal in many states.

More Power Vs. Usable Power

Racers always want more power. Most people assume that going faster automatically requires making more power. People who were in the diesel industry before they got into drag racing might disagree, but those of us who “discovered” oil-burners after years of racing everything else believe that a 14-second truck already has enough power to go faster: These rigs typically put out 450 to 500 horsepower at the rear wheels. The trick is applying the power in a way that’ll kill a Mustang off the line.

Planting what you already have moves the focus from the powertrain to the chassis. But before we get to that, novice diesel racers often think that four-wheel drive is best for off-the-line traction. In stock form, a four-wheel-drive is faster than a 4×2: having all four wheels engaged controls rear wheelhop during launch. For real racing, though, a 4×4 isn’t the way to go. Besides the extra weight, the drivetrain will begin to spit parts as the truck gets into the 12s. To put it another way, a two-wheel-drive that transfers weight correctly is faster than a 4×4 that makes the same power.

The most obvious way to help get more power to the ground is through traction treads. DOT-approved drag radials are the answer here [Mickey Thompson, McCreary and M&H are a few manufacturers]. Even though these radials are road-rated, I don’t recommend commuting on them – save the drag tires for fun only.

Traction bars are also critical for controlling wheelhop. I haven’t tried them all, but CalTracs from Calvert Racing transfer weight better than anything else I’ve used. Another modification for improving weight transfer is a pair of 80/20 front shocks [80 percent jounce, 20 percent rebound]. These allow the front end to lift, which really plants the rear tires. Stiffer 90/10 shocks are even better for racing but give a hard ride on the street.

Controlling wind is another way to go faster without having to increase power. Putting the tailgate down is the easiest way to improve aerodynamics [For safety reasons, most tracks won’t let trucks run with their tailgates down, so some racers leave their tailgates in the pits]. Adding a tonneau cover accomplishes the same thing. I don’t have any test numbers but estimate that removing the tailgate or adding a tonneau saves around two-hundredths of a second. Tonneau style doesn’t seem to matter, and I’ve seen an aluminum-framed Downey vinyl tonneau hold up at 160 mph. Front airdams also help. However, they must be over three inches above the ground in order to properly stage the truck at the timing lights.

Into The Low 12s

The suspension, tire, and body modifications mentioned above plus bolt-on engine additions should be enough to get well-maintained late-model 4×2 diesel pickups into the 12s. However, additional parts and labor are the next steps toward the low 12s or possibly even the high 11s.

First, basic head-porting-matching the ports and unshrouding the valves-will improve breathing. Next is swapping in a camshaft with a grind that’s racier than stock to improve turbo spooling and higher-rpm power but still remain streetable [kind of like putting a hydraulic roller setup in a street machine]. Cummins examples include the Helix from Formula 1 and MotorsportsSupply’s MaxSpool.

More fuel is the next step. Diesel is different from gas: It needs to be rich instead of lean for maximum flat-out acceleration. “Stacking” a performance module with a tuner/programmer is a good way to make the engine run richer. Choose aftermarket electronics that bump up the rail pressure and modify the bypass for adequate fueling. After racing, the computer can be reprogrammed with a less-aggressive tune so that the truck can be driven to work and get 20 mpg.

An aftermarket lift pump is another key component for feeding enough fuel to turn 12s. Aeromotive is one manufacturer, and other systems are available that include dual filtering to remove water. The OE fuel lines still work fine at this point. In my opinion, the stock injector pump is also okay for a street truck. Some people in the industry might disagree, but I don’t think that a modified pump is necessary for a truck that’s driven mostly on the street: Why risk over-fueling and burning it up?

Now for the expensive part: Once the truck starts lashing up, parts tend to spit back. Stock transmissions aren’t designed for drag-racing 6,000-plus-pound vehicles that put out around 500 horsepower. Here again, there’s an off-the-shelf solution – a tough but streetable aftermarket transmission from companies such as NADP, Sun Coast, and ATS.

At The Track

Safety requirements vary from track to track. Generally, additional safety equipment won’t be required for most street-legal diesels, even at DHRA-sanctioned events: no helmets, fire jackets, SFI belts or rollcages.

That covers the parts that diesel enthusiasts need to buy [hopefully from you if you’re in that part of the performance business] to go as fast as possible while staying streetable. After that, it’s all fun and games. Diesel owners should plan on a 50- to 60-pass learning curve, which is a total blast. Driving techniques that require practice include foot-braking and how to “cut a light.” Bench-racing with other enthusiasts and industry experts helps, but trial and error is how everybody ultimately learns to get the most out of their diesel trucks. By making changes after every run, diesel owners refine their driving techniques and can experiment to find out what tire pressure works best for their trucks.

This sport is still in its infancy, and I learn something new every day. At this point in time, the modifications mentioned above are about as far as I feel you can go before moving up to a race-only vehicle. Then we’re talking about a tube chassis, bigger turbos, high-flow injectors, modified injector pumps, nitrous oxide, water/methanol injection, and other things that turn the vehicle into a full-blown race truck.

The diesel segment is in a unique position right now. By offering off-the-shelf performance parts [many of which are owner-installable for the mail-order market or straightforward jobs for truck-performance shops], the diesel-performance industry makes it relatively easy for a grassroots motorsports novice to run 12s on the weekend, then drive the truck to work on Monday. A fast street-legal truck is a fun toy that appeals to enthusiasts from 16 to 60 years old.