The Outer Limits: Inside Diesel’s Most Extreme Competition Engines

About 15 years ago, diesel truck engines were around to be sure, but they weren’t considered in any sort of performance category. Sure, there were diesel tractors that made some pretty good power, but pickup truck engines? Nah. That’s all changed. Cummins engines have led the way, with the legendary 5.9L 12-valve making 1,500 hp in the mid 2000s, which is pretty dang good, considering that it was originally offered at 160 hp in Ram pickups.

“The legendary 5.9L 12-valve, originally offered at 160 hp, made 1,500 hp in the mid 2000s.”

How They Did It

Early sled pullers switched to big compound turbos, enormous injectors, and modified injection pumps to hit some big horsepower marks. 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…

2,000 Horsepower At Least

Nowadays, you have to bring at least 2,000 horsepower to the party to be in the big power crowd, and there are rumors that many trucks are getting close to 3,000 horsepower, all with engines that are at or around 400 cubic inches. In other forms of motorsports, 600 to 800-cid engines are commonplace, and most don’t make nearly the power that these diesels do. So how do these engines make so much power?

“Many competition trucks are getting close to 3,000 horsepower.”

The Engine Block

As nuts as it sounds, Duramax, Cummins and Power Stroke engine blocks can all be built to withstand 2,000 horsepower. Remember that 1,500 hp we talked about a bit ago? Well, Cummins engine ran into some big problems in the 1,500-1,800 hp range with too much cylinder pressure, timing and boost, and would rip the top third of the block right off the engine. Since most of the combustion pressure is in the top part of the block, it was a problem that needed to be addressed before advancing power levels. The solution was an old tractor puller trick, which involved installing a steel deck plate that would take the brunt of the cylinder pressure, and then machining and sleeving the block. The block would also be filled, effectively making it one solid piece with steel on top, which has proved to be very reliable.

While the majority of the engines approaching 2,000 hp are Cummins-based, there are a few Duramax and Power Stroke engines that have hit close to that number. Surprisingly, at these power levels, blocks such as those found on the 6.4L and 7.3L Power Strokes, or newer Duramax engines have been very reliable, especially with the installation of girdles and main studs, and filling the engine blocks.

For those wanting the absolute most a block can offer, there are also completely aftermarket blocks, such as the aluminum Cummins block available from Scheid Diesel, or the 7.3L CGI (compacted graphite-iron) piece from Hypermax. We also know of a run of aluminum Duramax engine blocks that have made their way into the hands of select racers across the country.

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. This has now all been addressed in the aftermarket, as forged rods, steel pistons and updated crankshafts are all available. Oddly enough the crankshafts are one of the parts that requires the least amount of modification, as many Cummins engines (as well as some Fords and Duramax units) are approaching 2,000 hp on factory cranks. Often, weight is actually taken out of the crankshaft on some engines (especially the Cummins, where more than 20 lbs. can be removed), while others just live with the weight, and fully counterweight the crankshaft for better balancing.

An interesting part of the new crop of maximum horsepower diesels involves 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. Other folks run near the stock compression (usually around 15.5:1) while a number of class-limited sled pullers actually raise compression up to 18:1 and beyond. This higher compression ratio helps spool up (and stay on top of) the turbo, while providing a bit more power than other 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 did weasel some info out of a few engine builders though, provided they remain anonymous. What we did find out is that the cam specs of many competition engines are just light-years away from original specs. 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 reason for the big bumpsticks is simple, as diesels can now make a lot more power at higher rpm levels, thanks to advancement in cylinder head design.

Cylinder Heads

Speaking of cylinder heads, this area is another part of extreme engines that has seen radical advancements over the last few years. Cylinder heads are available now for Cummins, Duramax and Power Stroke engines that are made from completely different castings, that offer more flow, better durability and consequently, more power. Competition diesel engines now are making more power at 80 to 120 psi of boost than they did at 150 to 200 psi a few years ago, thanks in large part to the cylinder head department.

Traditionally, a maxed-out stock casting would be limited to around 250 cfm, while now aftermarket heads are well over the 300-cfm mark (and some as high as 350 cfm). 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. Head gasket sealing has also been improved, with advancements in O-ringing and fire-ringing, as well as running sleeves with a slight protrusion out of the block, so the gasket just has to seal water and oil.

“Competition diesel engines now are making more power at 80 to 120 psi of boost, than they did at 150 to 200 psi a few years ago.”

Injection System

The name of the game in injection systems now is big, big, big. 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 combat this physical limitation, injection pumps have gotten bigger and bigger, from 13mm plungers and barrels, to 14mm, to 16mm. We’ve even heard of tractor pullers trying 20mm plungers or even larger, but there seems to be 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. Injectors of this size will flow roughly 800 percent more fuel than factory versions.

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 have also been advancing, and we know of a couple Duramax engines running four or even five CP3 pumps to try to keep rail pressure at maximum levels. There are also a couple of pumps out there that are off of larger engines that are being tried, but the owners mostly keep quiet about what they are, exactly.

Turbos And Intercooling

Another big piece of the “more horsepower” puzzle came with advancements in airflow on the turbocharger end. When pickup engines first started to make gobs of power, two large-frame turbos (usually with about a 100mm atmospheric turbo) would be used in a compound arrangement, along with water injection to control EGT. Now, most big horsepower engines run triple turbos (two into one) with atmospheric turbos in the 90-100mm range, along with water-to-air intercooling. Those who do run traditional “twins” now use atmospheric turbos in the 5-inch (127mm) range.

The air-to-water intercoolers that are now used were worth more than 100 hp as compared to water injection alone, and were a big step in performance. 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 were 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. There was a time where pulling motors at the highest level might only last a dozen passes until something gave way, but the current crop of 2,000-hp, or even 2,500-hp Cummins-based engines are very reliable, and can last a whole season. While rare, there are a few powerplants that are Ford or Chevy-based that are around 2,000 hp with some level of success, although not near that of the Cummins.

So what does the future hold? Well, we do know of a couple CGI-block 7.3L engines with mechanical pumps going together, and more and more Duramax engines (even in the 3.0-inch sled pulling class) are creeping towards 2,000 hp. Look for more advancements that are small but significant (like the water-to-air intercooling breakthrough), and for displacement sizes to increase if the rules allow it. 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