Inside Diesel’s Most Extreme Competition Engines
About 15 years ago, diesel truck engines were around to be sure, but for the most part they weren’t considered in any sort of performance category. Diesel tractors made some good power, sure, but pickup trucks engines? Nah. But that’s all changed. Cummins has led the charge, with a heavily-modified 5.9L 12valve that made 1,500 horsepower in the mid 2000s. That’s pretty good considering it was initially offered at 160 HP in Ram pickups.
“1,500 horsepower is pretty awesome considering the original design, but that’s light-years away from what’s out there currently.”
How they did it
To achieve big horsepower, early sled-pullers used compound turbos with large injectors and modified injection pumps. That’s with stock blocks, modified crankshafts, some industrial-spec pistons, and a few other tricks. Other traditional horsepower modifications like filled blocks, and O-ringed or fire-ringed heads were also used, along with high-tensile-strength studs and girdles everywhere. You might think that 1,500 horsepower is pretty awesome considering the original design, but that’s light-years away from what’s out there currently. What’s light-years? Oh, how about…
A Minimum Of 2,000 Horsepower
The big power crowd is now a group of trucks with 400-cubic-inch engines or more. In other forms of motorsports, 600- to 800-cid engines are commonplace, and most don’t make nearly the power that these diesels do. How can these engines generate so much horsepower?
The Engine Block
All Duramax, Cummins, and Power Stroke engines can be built to handle 2,000 horsepower. Remember the 1,500 hp that we discussed a while back? Cummins engines had some serious problems between 1,500-1800 hp with excessive cylinder pressure, boost and timing, which would tear the top third off the block. The problem was that the majority of combustion pressure occurs in the upper part of the engine block. This meant it had to be fixed before power levels could be increased. A tractor-puller trick was used to solve the problem. The steel deck plate would absorb the majority of the cylinder’s pressure. After that, the block was re-machined and sleeved. The block was also filled with steel, making it a solid piece. This has proved to be very reliable.
“Many trucks are getting close to 3,000 horsepower.”
Although most of the engines nearing 2,000 hp were Cummins engines, there have been a few Duramax engines and Power Stroke engine that have come close. At these power levels, the blocks found on the Power Strokes 6.4L or 7.3L, as well as the newer Duramax engine, have proven to be very reliable. This is especially true with the installation and maintenance of the main studs and girdles.
There are many aftermarket blocks available for those who want the most out of a block. These include the aluminum Cummins piece offered by Scheid Diesel or the 7.3L CGI block (compacted graphite iron) from Hypermax. Select racers have also been able to get their hands on aluminum Duramax engines blocks.
Rotating Assembly
Perhaps the hardest part of keeping an ultra-high-horsepower diesel together involves keeping the crankshaft, rods and pistons all where they’re supposed to be as they’re flying around the engine. Connecting rod failures and wristpin failures were common in the early days, as were pistons that couldn’t handle the stress. Aftermarket products such as forged pistons, steel rods and updated crankshafts have all addressed this issue.
On odd occasions, crankshafts can be modified to produce 2,000 hp. This is true for many Cummins (as also some Fords, Duramax and Ford units). Some engines have the crankshafts redesigned to remove weight. (Especially the Cummins which can lose up to 20 pounds. Weight can be removed from the crankshaft on some engines (especially the Cummins, where more than 20 lbs.
A new generation of maximum horsepower diesels has an interesting feature: the compression ratio. Many competition diesels run compression ratios of 12:1 or even lower, the theory being that there’s more volume in the cylinder to cram in a bunch of air without excess cylinder pressures. Some people run at or near stock compression ratios (usually 15.5:1), while some class-limited sled pulling teams actually increase compression to 18:1 or higher. This higher ratio of compression helps the turbo spool (and stay on) top, and provides a little more power than competitors.
Camshaft Specifications
If there’s one big secret in competition engines that builders keep close to their chest, it’s usually camshaft specs. We managed to get a little information out of some engine builders if they agreed to remain anonymous. The cam specs for many competition engines have been radically altered from the original specifications. While a “performance” street truck cam may be in the 180-200 degree range on duration, some competition engines are running as much as 260 degrees duration, and more than 0.800 inches of lift. The reality of the matter is it’s probably even more, as many people we talked to would only give us “last year’s” cam specs. The big bumpsticks are due to the fact that diesel engines can now produce more power when rpm is increased, thanks in part to advances in cylinder heads design.
Cylinder Heads
The cylinder head is another area of extreme engines where radical improvements have been made in the past few years. There are now cylinder heads available for Cummins Duramax Power Stroke that are completely different castings that provide more flow and durability and therefore more power. The cylinder head department is largely responsible for the fact that competition diesel engines can now produce more power with 80 to 120 psi than they could at 150 to 200psi just a few year ago.
The maximum stock casting is usually around 250cfm. Aftermarket heads, however, are well above this mark, with some even reaching 350cfm. While testing varies from flowbench to flowbench, the dyno numbers from those who’ve ran higher-flowing heads back to back are clear—they just plain make more power. With improvements in fire-ringing and O-ringing as well as running sleeves which protrude slightly out of the block to allow the gasket to seal only water and oil, head gasket sealing is also improved.
Injection System
Injection systems are now all about big, huge, massive. There’s only so many degrees of crankshaft angle you can inject fuel to make power, otherwise it just gets blown out the exhaust as heat, or creates too much cylinder pressure early and results in broken parts. To overcome this limitation, the size of injection pumps has increased from 13mm barrels and plungers to 14mm and 16mm. We’ve even heard of tractor pullers trying 20mm plungers or even larger, but there seems to be a point of diminishing returns. Injectors have also gotten more extreme, with many Cummins engine-based pullers running International injectors as large as “5x39s,” or five-hole injectors, with a .039-inch orifice. This size injector will deliver approximately 800% more fuel than the factory version.
Common-rail power hasn’t been left out either, as different injector bodies, extreme internal modifications, and very large nozzles have all upped the CR game in recent years. Pumps are also improving. We know that some Duramax engines run four or five CP3 pump to maintain rail pressure. Some pumps from larger engines are also being tested, but their owners are keeping quiet.
Turbos and intercooling
Another big piece of the “more horsepower” puzzle came with advancements in airflow on the turbocharger end. Two large-frame turbos, usually with a 100mm atmosphere turbo, were used in a composite arrangement to produce a lot of power. Water injection was also used to regulate EGT. Today, the majority of big horsepower engines use triple turbos with atmospheric turbines between 90 and 100mm. They also intercool with water to air. Those who do run traditional “twins” now use atmospheric turbos in the 5-inch (127mm) range.
Air-to water intercoolers were a major improvement over the old water injection system. They produced more than 100 horsepower. Water injection is still used however, and it’s the equivalent of about 20 low-pressure injection setups. More advanced “billet” compressor wheels for large-frame turbos have also made their way into the market, and again, have been shown to be worth more than 100 hp on certain applications. If you’re thinking that turbochargers and intercooling have been advanced across the board in all areas in the past few years, you’d be right.
What’s Next?
We’re happy to report that as extreme as all this may sound, it’s for a purpose. The Cummins engines that produce 2,000 or 2,500 hp are reliable and can last an entire season. There are some Ford and Chevy engines that can reach 2,000 hp, but they are not as successful as the Cummins.
What is the future? There are a few CGI 7.3L engines that have mechanical pumps and there are more Duramax engine (even those in the 3.0-inch pulling class) which are getting closer to 2,000 horsepower. Expect to see more small, but important advancements (like the breakthrough in water-to air intercooling) and larger displacements if rules permit. While it’s hard to accurately predict the future, if the past few years are any indication, we’re in for one heck of a ride. DW
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