It is one of the purest forms of American motorsports. One guy pulls up next to another guy at the starting line and revs the engine. A simple glance over, a nod and a green light.
In a fury of sound and smoke, the two racers take off down the straight stretch of pavement. If it’s got an engine and there is another one around someplace, someone will want to race it.
Only this time, it’s not the small block Chevy, 5.0L Ford or Hemi’s that are making all the noise. Nor it is the little pocket rocket four-bangers coming in so many great little domestically badged sport compact cars. To be sure, they’re coming from the Big 3, but think about Dodge Cummins, Ford Powerstroke and GM Duramax-powered pickups lined up in a drag strip’s staging area as far as the eye can see, ready to launch down the quarter-mile – often in 4WD – to 14-, 13-, 12-, even 10-second (and under!) runs.
Although embraced so far by a relative few, the practice of drag racing diesels has been making a slow but steady assault on the strips of America and offers performance engine builders a real opportunity to make some noise.
Drag Racing Diesels?!
It’s often a shock to learn that the phrase “diesel engine on the track” isn’t necessarily talking about just sled pulling trucks or tractors anymore. Yet it shouldn’t be surprising. Diesel engines are known for their strength, power and durability. With relatively minor adjustments to their internal components and the addition of or modification of external power adding parts, diesels can provide a stunning display of drag racing potential.
Diesels and gas engines differ in more ways than just the fuel they use to operate, of course, but it is those differences that can make diesel drag race engines so attractive.
Using either carburetion (where air and fuel are mixed together before entering the cylinder) or fuel injection (in which the fuel is injected outside the cylinder before the intake stroke), a gasoline engine ingests a mixture of gas and air, compresses it and ignites the mixture with a spark. A diesel engine takes in just air, compresses it and then injects fuel directly into the compressed air. The heat of the compressed air lights the fuel spontaneously.
The compression ratio of a gasoline engine is typically between 8:1 to 12:1, while a diesel engine uses a compression ratio of between 14:1 and 25:1. The higher compression ratio of the diesel engine leads to better fuel efficiency, which is great. But because it doesn’t require the heat of a spark plug, the problem of detonation is also eliminated, meaning that turbochargers are great additions (and, in fact, standard on every production diesel truck engine), giving factory-supplied boost in the 25-30 psi range.
“The problem most diesel guys run into is that they’re always thinking about the torque of a diesel,” says Greg Hogues, diesel engine builder and drag racer. “In drag racing you don’t want the torque – you want to use whatever horsepower you can get and rev the engine up.”
Hogues, who has developed engines and raced a diesel pickup for several years, believes that because of this horsepower bias, gasoline engine builders are in a great position to build diesel drag racing engines…perhaps even easier than their diesel-expert brethren. “The problem with a lot of diesel guys is that they need to learn to run these engines as a tuner would. You need to learn to rev the engine up. It’s time to get away from the ideals of torque; get into the rpms and make the thing accelerate.”
Hogues says “Diesel people seem to be of the firm opinion that cylinder head development and camshaft improvements are stupid. ‘Why would you want to do that? You just put a bigger turbocharger on.’ Yet, with my last race truck, we worked carefully on the Cummins cylinder heads, the camshafts and the valvetrain geometry. We got the motor to where we would turn the engine 6,000 rpm, and I went 8.72 at a national event. I eventually ran an 8.62, and a buddy of mine then turned an 8.44 – the thing will go 7.90 before it’s all over. Oh, and that’s at 160 mph, top end.”
Ray Little, of RayMac Racing Engines in Texas, has a long history of building a variety of gasoline engines. “I started in a reman facility long ago, building all sorts of different passenger car gas engines. That got me into building engines for GTP racing, Trans-Am and NASCAR race cars, and then I worked at Reher-Morrison doing drag motors.”
Until recently, Little says the diesel market was strange to him. But while it may still be below many engine builders’ radar, the opportunities will continue to increase. “It’s a market that has just taken off over the past couple of years,” he says.
Little has been working with Hogues to push diesel development further along than it has been, and Little admits that, for a gasoline guy, it’s been very enlightening.
“I guess it’s because diesel burns much more smoothly than gasoline, much more controlled, further down top dead center. It still amazes me about the power levels we’re making and how little stress the bottom end of the engine actually has. Even with smaller main bolts, less clamp load on the bottom end, and with way more cylinder pressure, the caps don’t walk around nearly as much.”
Little says he’s still amazed by what he sees, although he’s beginning to accept it: “A gas motor guy would look at the power these motors make and think there’s no way the bottom end will stay in it. That’s just the way I was.”
To put it in perspective, Little points out that diesel drag motors often turn in excess of 6,000 rpm. “That’s twice what they were designed to do. Considering how heavy the reciprocating and rotating weights are on these things, it G’s out to tons! But the parts are so robust and built to last, I’m not sure where the limit is.”
Machine Shop Magic
Another gas engine expert who has turned his attention to compression ignition engines is Gale Banks, of Gale Banks Engineering. His goal in developing a new generation of engine is combining his years of gasoline performance and applying it to a diesel to make it more gas-like. All current diesels make torque over horsepower at a 2:1 ratio and gas engines have a 1:1 ratio of torque to horsepower. My goal is to make a diesel that has a 1.5:1 ratio of torque to horsepower. The main thing is to maintain the torque advantage but get rid of the current weight.”
The changes that Banks has implemented for (in this case) a Duramax, include reducing the weight of the rotating mass and its resistance; lightening, knife-edging and contouring the crankshaft; and giving the counterweights an “aero wing” shape, with a blunt leading edge that trails to the tail end.
Other internal changes included replacing the stock connecting rods with 4340 billet steel H-beam connecting rods that have been both polished and shot peened. Changes to the oiling system included adding oil pathways to the block where none existed, to help the engine withstand the increased loads and higher rpms than they had been designed for.
“There are great opportunities for people to build these motors,” explains Hogues. “The problem that many people face when they start working with them is they think about them wrong.”
Internal parts aside, say our engine building experts, some of the most important upgrades include a simple change of attitude.
“The first thing you need to do is upgrade to premium engine studs, rather than head bolts. Plus, with the diesel, guys assume they’re so rigid that you don’t need to worry about torque plates. When Ray and I started working together, I didn’t believe torque plates were necessary. I thought the block was so heavy it would never flex…but after I machined the cylinders I found it was way off,” Hogues admits.
“Just look at the numbers,” he says. “The Cummins block doesn’t weigh as much as a big block Chevy! The Duramax bare block weighs even less. Once I saw how much those diesel blocks move it just blew me away. Torque plates are absolutely necessary.”
Another problem some performance engine builders face when building diesel drag race engines involves the practice of O-ringing the cylinder heads. “Designed for drag racing heads, a lot of people think it’s necessary for diesels, too,” Hogues says. “But too many times, even from the big shops, the protrusions are wrong, the receiver grooves are wrong. They have to retorque the heads four, five or six times, thinking the head studs are stretching. What they’re really trying to do is press the thing into the stainless steel fire ring on the head gasket.”
If you’re going to do it, says Hogues, it’s best to put the grooves in using a mill. But it’s not always necessary. “Boring these blocks correctly is critical,” says Hogues. The reason they can’t hold head gaskets on them is usually because of faulty machine work. They’re not using torque plates, they’re not putting O-rings in right. If you put the thing together correctly, you can use a stock MLS head gasket and ARP studs.”
Another aspect of diesel performance that many engine builders don’t understand, according to experts, is the impact of nitrous oxide on the system.
“Nitrous has the opposite effect on a diesel than it does on a gas motor,” says Hogues. “Diesels are naturally oxygen deficient and nitrous has oxygen in it, so it actually serves as an intercooler and cools down the combustion process. It actually makes it safer.”
Because the fuel is packed so tightly in the combustion chamber, some of it isn’t burned until during the exhaust stroke. “You get heat going out the exhaust valve, which is why you see the smoke,” Hogues says. “That’s where these things burn up – they are running too fat. You can’t run them too lean, and nitrous helps a lot because it helps burn the excess fuel.
While some of the concepts may change, a skilled engine builder or machinist can adapt to the diesel world with relative ease, believes Hogues. “You just need to realize that everything you do for a gas motor will work for a diesel engine. Everything. Camshafts, head work, it doesn’t really matter. It shouldn’t be a big deal. There’s nothing they can’t do.”
Little says that, since his baptism in diesel fuel, he has built most of the popular powerplants, but tends to focus on the Cummins. “They’ve all got a few weak points. The rocker systems aren’t perfect in any of them. At this point, even at 6,000 rpm, they haven’t been an obstacle, but they tend to worry me. We’re trying to find a more efficient system.”
Additionally, Little says, the rod/piston combination in the Powerstroke seems to be its weak point. The Duramax seems to be in the same boat. “But they’ve beefed up the rods and the pistons and now they’re getting forged parts, so durability should improve,” he says.
“It’s just a matter of making sure the components are there to get the fuel to the engine and making sure the bottom is robust enough to support it. Unlike high performance gas engines, lighter isn’t necessarily better,” Little cautions.
Of course, all the standard parts that are needed to rebuild a diesel engine are available, but are performance parts available in the diesel aftermarket to upgrade these engines? According to Little, the answer is a qualified “maybe.”
“Bolt-on parts, like turbochargers, intake manifolds, fuel pumps are available, some of which may come from bigger diesel engines or some from custom castings, and there are companies making rods and pistons today, but we don’t have the performance cylinder heads or crankshafts,” he says. “All of the development has gone into the bolt-on parts and the electronic tuning required to keep the efficiency.”
Little reminds his fellow engine builders that when making the move to diesel, one of the biggest hurdles to overcome is the mindset. “You have to rethink a lot of what you know – this is essentially an air-cooled engine. It forces you to take a step back and look at the advantages and disadvantages…almost like looking at the differences between a 2-cycle and a 4-cycle engine.”
It’s not uncommon, due to the lubricity in the fuel, to tear a standard diesel engine apart at 200,000 miles and turn it into a performance monster, says Little. “You simply rework the compression, put valve pockets in, replace the rings, rework the ring tension, use some coatings, open up the clearances, hone the stock bore (which will probably still have its original crosshatching) and button it back up. It’s already lived a life and now you’ve quadrupled its power.”
Little says its easy to make such an engine turn at 6,000 rpm, producing 800-900 hp. “And that’s normally aspirated! Imagine what happens when you hit the nitrous!”
This is a great opportunity for low-buck drag racing, Little explains. “You can easily take a farm truck and make it into a dragster. It takes a little acceptance, but the first time you see a one-ton crew cab dually blow a Z06 off the line, you’ll be a believer.”
A History of Diesel Engine Development
In 1893, Dr. Rudolf Diesel, a Bavarian scientist, patented a design for an internal combustion engine, which was termed a “Diesel” engine. He considered previous internal combustion engine failures and applied himself to designing an engine to operate on an entirely different thermodynamic principle.
Using the mechanics of the 4-stroke cycle, Dr. Diesel proposed that only air be drawn into the cylinder during the intake stroke. The compression stroke was to compress the air in the cylinder to a high enough temperature to induce ignition and combustion without the use of added heat (spark). It was the original Dr. Diesel’s theory that if the rate of injection were properly controlled during the combustion phase, combustion would occur at a constant temperature.
A single-cylinder working model was constructed and first experiments were conducted using coal dust for fuel. All efforts to build a working model on the cycle proposed by Dr. Diesel resulted in failure. Consequently, an engine operating entirely on the theoretical cycle proposed by Dr. Diesel was never produced. This cycle subsequently became known as the diesel cycle.
Many designers realized the value of the practical elements outlined by Dr. Diesel. Subsequently, experimenters began to achieve favorable results by eliminating the impractical elements and altering the cycle of operation. By this time the more volatile petroleum fuels were more commonly used and diesel engines were designed to run on liquid fuel. These engines operated on a cycle in which the combustion phase occurred at constant pressure rather than at constant temperature. Designers also found that it was essential to cool the combustion chamber externally.
Progress in diesel engine design has been rapid since the early models were introduced. The demands of war, progress in metallurgy, fabrication, engineering and refinements in fuels and lubricants have all served to produce modern, high-speed diesel engines of exceptional efficiency.
|The Diesel Hot Rod Association (DHRA) is dedicated solely to diesel motorsports competition.
The DHRA organizes drag racing and sled pulling competitive events. These events include member track bracket drag racing series, our sportsman sled pulling series, our national Pro Diesel Shootout series, and national events. The national events combine sled pulling, drag racing, dynamometer and burn-out competitions and a vendor fairway; these events bring diesel competitors, fans and vendors/manufacturers together in one place.
The DHRA is an NHRA-approved alternate sanctioning organization, that works with both NHRA and the SFI Foundation when developing its rules to ensure, as much as is reasonably possible, the safety of its competitors, fans and sponsors.The sanctioning body has networked with tracks and motorsports officials and is today the only sanctioning body outside the NHRA and IHRA to have member track across the country.
For information contact: Diesel Hot Rod Association (DHRA) 765-768-6400; www.dhraonline.com
There are other diesel drag racing resources available as well, including: