By now, you’ve probably seen the video of the massive dyno explosion in which Firepunk Diesel’s Pro Stock diesel engine comes apart in spectacular fashion. If you haven’t, stop reading and watch the video above; we’ll wait.
“At this point we don’t have a definitive reason,” says Firepunk’s Lyn Miller. This isn’t surprising, given that the explosion had only happened 24 hours prior to our conversation. “We were able to recover the datalogs from the run, which took a bit, since the wiring harness and everything was destroyed. We can’t see anything irregular in the data log.”
Like any explosion investigation, the Firepunk team has been reviewing the videos, frame by frame, trying to piece together exactly what happened to try and shed some light on the subject.
“Looking at the slow motion videos, you can see a puff of smoke up at the head gasket, and the cooling lines jumped,” Lyn says.
“So it kind of appears that we might have gotten combustion into the water jackets. We have a few theories, but nothing concrete right now.”
One thing that contributes to the mystery is the fact that at the time of the failure, the engine was below its performance ceiling.
“On the dyno, we were doing short little 4,500-rpm holds. Basically we free-rev the engine to 5,000 rpm and then load it down to where it holds it at 4,500 rpm as you feed it throttle. It comes out to be a two or three-second power run. It’s pretty tame on the engine compared to some of what we do.” says Lyn.
“Horsepower and torque-wise, we weren’t anywhere close to any boundaries or pushing anything hard enough to fail. We were at about 2,200 horsepower and we make that every time we go down the track. We were at 2,500 foot-pounds of torque at the time of the failure, and we make 500 more foot-pounds of torque during a pass at the track. It wasn’t like we were trying to exceed any limits on this run. This seems like there was a catastrophic event of some kind.”
Miller walked us through some of the team’s theories and thoughts regarding what happened.
“Whether it lifted the head or had a fire-ring failure, and allowed combustion gasses into the cooling jackets, or we got water into the cylinder and hydro-locked a cylinder – we really don’t know,” Lyn says.
“There are so many different ‘could be’ issues – cylinder pressure, timing issues, crank flex. We’ve done some testing with Fluidampr, and at 1,500 horsepower we were seeing 3 degrees of crank deflection, front to rear.”
While it was only the third pull of the day on the engine, there had been a hiccup prior in the day.
“This was the third pass on the dyno. On the first pull, there was a small glitch where the crank momentarily lost signal, but that showed up on the data log from that pull, and nothing like that showed up on the data log of the kaboom pull. Plus the issue was corrected before the second pull, and the second pull had no issues,” says Lyn.
An interesting piece of the puzzle is that the video clearly shows the catastrophic event occurring at the back of the engine, and that coincides with some previous engine testing the team had done.
“We’ve put some effort into monitoring some of the harmonics on the engine before. We had an oscilloscope on the crank signal sensor, and we could see each combustion event, and see the acceleration and deceleration of the crank through its rotation,” he says.
“One thing that the crew at Exergy noticed is that when the number six piston fired, it accelerated more than the other five cylinders. There might have been something there, since it seems that like that’s where the failure started.”
While the forensic analysis of the failure is still ongoing, Lyn readily admits that they may never know the exact cause of one of the nastiest dyno explosions we’ve ever seen.
“Ultimately it came down to a block failure. However, we really aren’t sure what caused the catastrophic event that led to it. It was a cast block, and it might have been fatigue mixed with a casting flaw, but I have my doubts about that. We’ve got an amazing fire-ring design and oversized 9/16-inch head studs, so we’ve got a solid setup, but we definitely want to incorporate a method of direct cylinder pressure monitoring going forward,” says Lyn.
What was supposed to be an easy off-season for the Firepunk crew–consisting of some light parts testing and combination refinement–has turned into a complete program overhaul.
“We not only broke the engine, but we tore up the custom wiring harness – which is estimated at about 40 hours of labor to repair – we broke our fuel rail, the custom gear drive timing cover, one of the turbo covers, and I’m going to have to refabricate most of the turbo piping,” says Lyn.
“It really wrecked a lot of stuff. There were holes in the dyno cell, and the room was covered in oil. Every time we turn around we realize something else is destroyed by the explosion. Luckily this happened on the dyno and not in the truck, because that could have been nasty.”