Often times, when someone is boasting about how much power their engine made, it only made that number once and under ideal conditions. However, when you are using the engine for a specific purpose, a moon-shot dyno sheet that you can use to impress people online doesn’t mean much. How the engine performs in use is where it matters.
Sometimes, the requirements for the performance envelope are a bit more extreme than usual. Enter champion jet boat racer Mark Rodacker and his collaboration with Tom Nelson of Nelson Racing Engines. Rodacker approached NRE with a unique rulebook to follow, and set of durability requirements.
“The class rules allow 470 cubic-inches, naturally aspirated,” explains Nelson of the River Racing Jet Boat ruleset. “Then, there’s a little clause in there that says you can run twin-turbos if the engine is 260 cubes or less. I felt like we could make way more power with a twin-turbo LS than with 470 cubic-inches naturally aspirated in this class.”
However, more than just building an engine to exploit the rulebook, Rodacker has a very specific set of durability criteria for the LS engine – to be able to run wide open on the dyno for five minutes at a time. To compound that insane feat, it had to be done a dozen times.
“We’re going to attempt to make a twin-turbo LS run flat out at full boost and wide open throttle.” says Nelson. “We’ve got to run this thing for five minutes, at wide-open-throttle, under boost, at over 7,000 rpm. This engine is really a prototype to see if this is possible.”
While the full build sheet isn’t for public consumption yet, Nelson does reveal a couple of the more interesting points of the build. “This thing is filled with goodies,” he laughs. “We’ve got NRE Gen 2 60mm ball bearing turbos and an insane big oil cooler, because when you run for this long things get hot.”
When Nelson calls something “insane”, you know it has to be impressive. Because of the engine’s intended application, the extensive use of water-cooling helps keep the massive temperatures generated by extended WOT runs in check. “We have water running through the oil cooler, and double-wall water-cooled headers.”
The combination is run by a Holley EFI box that appears to be some variant of the Terminator ECU. “Holley has been really involved in this project. We’ve got scramble boost both up and down, so he can push a button and pick up another 200 horsepower to get around someone, and if he just wants to cruise and save the engine, he can bump it down 200 horsepower,” says Nelson. “The engine can vary from 800 to 1,200 horsepower during the race with a couple button presses.”
While the power numbers for the engine are impressive – 1,200 horsepower from only 260 cubic inches makes for a stout 4.61 horsepower-per-cubic-inch (281.69 horsepower per liter, for you metric types) – the main goal is endurance.
“It’s a crazy combo. 260 cubes making 1200 horsepower on an endurance level. The power numbers are killer, and way better than anything anyone is making naturally aspirated in the class,” says Nelson. “But the question is, can this engine survive and live. That’s what we’re testing here with these long, long pulls.”
Watching the video above, that is only the first five-minute-long pull of twelve scheduled. There’s something about a five-minute-long dyno pull that is both mesmerizing and terrifying at the same time. Then realize, that is only about eight percent of the full hour of WOT, full-boost, 7,000-plus rpm that will be required to prove this engine design.