Oftentimes, much of the magazine industry tends to focus their efforts on performance parts for fairly stock trucks—mainly those that will bolt on without major internal engine modifications. But what about the “rock stars” of the industry—the all-out sled pullers, drag racers or dyno kings? Sure, we feature these vehicles, but what does it actually take to build a true race-winning diesel? The following should give you a good general idea as to how to build an all-out race truck!
How To Build A Diesel Drag Truck Engine
Most of the serious diesel drag racing trucks find themselves in the 10, 9 or even 8-second bracket in the quarter-mile, which means they have somewhere around 800 to 1,400 horsepower at the wheels. While there are a few ways to accomplish this, some are better than others. For turbo selection, competitors are all across the board, with some running big single turbos, while others are running triple turbos. While there’s no “right” choice, running compound turbochargers allows for a tighter torque converter, allows for quicker spooling at the line, and are more manageable coming off the line than rigs with larger compounds or singles.
“Go with the lightest truck possible. And drag radials or slicks are a must.”
Engine speed is another area that varies greatly, with some trucks shifting as soon as 3,000 rpm, and others wringing it out until 5,000 rpm. Again, there’s no right answer, but a higher engine speed produces less torque at a given horsepower, which again is easier on transmissions. If it were us building a diesel drag truck, we’d use a large displacement engine with moderately sized compounds, and a small shot of nitrous. Something like a 6.7L Cummins or 7.1L Duramax stroker with a 63.5mm small turbo, an 88mm large charger, and a couple stages of spray.
The transmission area is probably the toughest part of building a drag race vehicle, as many enthusiasts can attest to. We talked to one competitor who had spent more than $50,000 in transmission parts over the years, trying to get things right. Automatics rule down the quarter-mile, and virtually every serious drag racer runs them. While there are planetary-gear manuals that can be shifted without a clutch (like a Lenco or B&J), their price tag usually excludes them from the picking. No matter whether it’s a TH400, 47RH, Allison or 4R100, drag racing transmissions have a lot in common including billet input, intermediate and output shafts, higher-stall torque converters with additional lock-up clutches, and serious transmission coolers.
Other go-fast items such as trans brakes or manual valve bodies are available for the racer who wants more control over their truck. One good setup would be a Dodge 47RH or 47RE transmission, with an automatic valve body and a host of billet parts. The converter would be a high enough stall speed that the small turbo should light within a few seconds, and not struggle against the converter, and taking forever to spool. At the highest levels of performance (1,000+ rear-wheel horse power) transmissions will still need to be regularly checked for wear.
Chassis and Drivetrain
The first question on everybody’s mind, chassis-wise, is whether they should go with a two-wheel drive or four-wheel drive truck. Again, here the answer is muddled, as either one can get the job done. What people should do is go with the lightest truck possible, like a lot of the regular cab short beds we’re starting to see pop up. Drag radials or slicks are a must, and proper suspension tuning that allows the truck to leave the line hard without bouncing. While it goes against the current trend of two-wheel drive trucks, here we’d go against the grain and build an ultra-light (4,500 lbs. or so) four-wheel drive truck, as the initial traction advantage, braking advantage for staging, and ability to steer the truck if it gets loose rather than lift off the throttle makes the four-wheel drive a good choice for most slippery diesel tracks.
Final Thoughts: Drag Trucks
Perhaps the most overlooked part of building a diesel drag truck is the practice. Competitors make change after change, and then just show up at the track and hope everything works. Testing is an all-important part of the sport, and racers should test as much as possible in order to dial in their combination.
When it comes to building an engine for a pulling truck, the first question will most likely be “what class will you run in?” Since most sled pulling is rule-based, and involves limiting turbo size, many pullers build a specific combination for a specific class. As of right now, 2.5, 2.6 and 3.0-inch turbo classes are the most popular, with some of the upper echelon of trucks competing in Unlimited Single Turbo classes or Super Stock (multiple turbos and cut tires allowed) classes. For most, they’ll be building a 2.5, 2.6 or 3.0 class truck, so we’ll focus on that. First off, the engine must be able to spin some rpm. With pulling, the entire run is often done in one gear, which also means the engine must have a decently wide power band.
“2.5, 2.6 and 3.0-inch turbo classes are the most popular.”
It’s here that mechanical trucks do well, as their injector design lends into making bunches of high-rpm power. Many pullers will leave the line at 5,000 rpm or even higher, and slip the clutch out until the engine is dragged down until about 3,500 rpm. This means the engine will need to be built extremely strong, and turbochargers will normally be very expensive. An upgraded HX60 Holset that has been modified into a 2.6 turbo can cost $4,000 to $8,000, but right now that extra bit of power over the competition is what’s needed to win. Our choice here would be a 12V Cummins engine with a 13mm pump and supporting modifications to turn 6,000 rpm, along with whatever turbo fit our class.
How To Build A SLED PULLER
As a polar opposite of drag racing, manual transmissions exclusively rule sled pulling. While automatics may be found here or there across the country, almost everyone in a competitive Midwest points series runs a manual. Many of these transmissions are simpler than one might think, as a Dodge NV4500 for instance, can handle an immense amount of power with just an upgraded input shaft, and a dual or triple-disc clutch. ZF6s, NV5600s and other models are similarly strong, although aluminum-case transmissions such as G56s can often break with big power. We’d run the stout NV5600 with a triple-disc pulling clutch, because in sled pulling there’s no such thing as overkill.
Chassis And Drivetrain
When building a pulling truck, having as long of a wheelbase as possible, having as much weight over the front as possible, and having as rigid of a chassis as possible are all benefits. With up to 40,000 lbs. in tow, the axles of the truck must also be upgraded, as failures are fairly common. A lot of serious 3.0 class pullers will run Rockwell axles or something similar in size, because of the incredible strain. Building a ladder-frame section to the chassis is also very common. A Dodge Mega Cab body and frame from a salvage yard would be one of our first chassis choices, with upgraded axles and differentials both front and rear.
Final Thoughts: Sled Pullers
It’s not that newer electronically controlled common rail trucks won’t work well because they do, it’s just that we’ve seen a strong resurgence of the mechanical trucks helped by the backing of many serious shops devoted to their performance. And in sled pulling perhaps more than any other diesel sport, the help of shops, friends and family must be secured before a competitive truck can be built.
“For a street vehicle, 600-800 rwhp is hard to beat for the fun factor.”
While competition vehicles are awesome, building a fast street truck is perhaps the most common dream among diesel enthusiasts. And again like drag trucks and sled pullers, building a street demon has a few formulas that work rather well. For starters, the engine we’d choose would be a common rail, thanks to the immense variety of tuning available for them. The tuning is so advanced in fact, that a tough, medium-sized single turbo such as the BorgWarner 67.7mm S400 can be used to make upwards of 800 horsepower. On a street vehicle, 800 rwhp will feel crazy fast, and will still spool-up quickly enough to be fun to drive. It’s also a horsepower level that often (but not always) can be run without a full engine build, rather just head studs and a few other supporting modifications. For a street diesel the 600-800 rwhp range is hard to beat for the fun factor, and usually will be pretty reliable unless the truck is abused.
How To Build A WILD STREET TRUCK ENGINE
Unlike the drag truck and sled puller builds, either a manual or an automatic can be used in a hot street truck. They both have their advantages, and disadvantages, however. A manual transmission is usually cheaper to build for high horsepower; in many cases just requiring a stout clutch. When a larger turbo is used, they also offer the advantage of winding out gears, to use every last bit of engine speed. However, large pressure clutches can also be hard to shift, and jerk at low speeds. Automatics on the other hand can be pretty smoky if the shift timing isn’t altered, are more expensive to build, but are easier to drive. In the end, the choice here is up to the truck’s owner, and whether he wants to go drag racing or sled pulling with his daily driver.
Chassis And Drivetrain
One of the great parts of making a diesel have more power is much of the suspension, chassis and drivetrain can be left alone. In a street application, the axles, suspension, transfer case, frame and cooling systems are all up to par at higher horsepower levels on most street trucks. Gauges are a must to monitor the engine, and a positraction unit is a worthwhile investment if your truck doesn’t have one. Other than that, they’re pretty much ready to pour on twice the factory power, with just engine and transmission upgrades.
Final Thoughts: Wild Street Diesels
Fords from the 7.3L engine on up, Duramax-powered GMs, and all years of Cummins-powered Rams can be made to handle 400-800 rwhp, and still be streetable. This is perhaps one of the most exciting parts of owning a diesel, as a 7,000-lb truck with 700 rwhp can scoot from 0-60 mph in about 3.8 seconds, which puts it in pretty fast company, like the Corvette Stingray (3.7 seconds), the 707-hp Challenger HellCat (3.7 seconds), and the ZL1 Camaro (3.9 seconds). On the street where the surface is un-prepped, it’s not even a race as the diesel will easily win, all while being able to seat a group of people, tow a trailer, or haul a load of bricks. And that’s what having a hot street truck is all about. DW