Recently, we brought you Rob Dahm’s naturally aspirated dyno session of the wild 12-rotor engine we first brought to you over a decade ago. Without boost, Dahm has the engine making about what it did in its original carbureted form. However, the main goal of Dahm getting this 960 cubic-inch engine up and running isn’t just to dial in an EFI swap, but rather to add some boost to the engine and really let it eat.

Just to recap, each of the twelve rotors displaces 80 cubic inches and is grouped into three four-rotor banks. That makes for three 320 cubic-inch engines, each fed by a 106mm T6 Garrett G55 turbocharger. This engine is capable of moving some serious air. The insane combination is controlled and monitored by a Haltech engine management system.

No one involved in this project expected it to be easy. However, the challenges leading up to this dyno session at Vrbancic Bros. Racing have been quite challenging. But, with all of the kinks seemingly sorted out, it was time to actually allow exhaust into the massive 106mm turbines — yes, three of them. The first pull was not a power pull, per se, but just a 3,000 to 6,000-rpm jaunt with the wastegates wide open to make sure everything was working right. Right out of the gate, Dahm was rewarded with 837 horsepower and 806 lb-ft of torque, along with a lot of blowby, due to an improperly sized dry sump system (the proper one is still being built).

What do three 106mm Garrett G55 turbos look like on a 12-rotor engine? That’s a 106mm turbo for each 4-rotor bank, for those keeping track.

Checking the 12 exhaust gas temperature probes, a problem child was identified — rotor 10 — which has some rotor-housing sidewall damage. Other than that, the rotors showed to be pretty evenly balanced, with each other, with one four-rotor bank coming in as a single trace. With a five-gallon pail set up as an oil overflow catch can, it was time for Dahm to bring the engine into a more advantageous RPM range.

The additional RPM led to an oil bath for the engine, which shut down the pull before the 8,000-rpm target. However, the data from that pull also gave Dahm the confidence to start adding some boost to the engine. Well, it would have been had the engine started — the engine’s ability to start when hot disappeared once again. While this time it was unrelated to the starter motor itself (which you’ll recall from the previous installment), it still ended the dyno session.

To call the 12-rotor engine rev-happy would be an understatement. A blip of the electronic throttle sent the engine to 10,000 rpm before the ECU could catch it.

Back to the drawing board, Dahm enlisted the help of a friend down under who specializes in rotaries, and with some run-stand testing, was able to figure out how to get the engine to light off when hot, without requiring any throttle input. Getting a little too comfortable with his throttle inputs on the run stand, Dahm zinged the engine to 10,000 rpm before the ECU could catch it. And with that, it was off to the dyno, once again. This time, a name that should be familiar to any of you reading this: Ed Pink Racing Engines.

With the engine back on the dyno, the first pull was only set to 6 psi of boost and 6,500 rpm. The third bank of rotors — 9 through 12 —was running so rich it was breaking up, but even with that, the numbers came in at 1,137 horsepower and 919 lb-ft of torque, which, as Dahm excitedly points out, is more than the engine has ever made. The next few pulls revealed that each bank of rotors wanted something different, fueling-wise. The center bank was demanding 40 percent more fuel at 5,000 rpm than the other two banks. It’s almost like a one of one 12-rotor engine behaves like a weird science experiment on the dyno. But, that’s what Dahm signed up for.

This 12-rotor beast has enough turbocharger, in theory, for almost 9,000 horsepower. While we don’t expect to see anywhere near that, we are extremely excited to continue following this engine once it’s in the engine bay of a dragster.

The next pull showed even more progress, save for a nasty dip at 5,750 rpm, making 1,302 horsepower and 1,146 lb-ft of torque. As Dahm points out, the giant Garrett turbochargers aren’t making boost until 6,500 rpm, and that’s where they are ending the pulls. So, the logical move is to spin the engine higher. Easier said than done, with this beast.

Stepping up the RPM to 7,500, another previous challenge reared its ugly head — oil leakage. This time, though, it soaked the fiberglass insulation blankets on the engine dyno and ignited in the dyno cell, causing some decent mayhem. However, amid the chaos of the fire, Dahm’s cameraman pointed out the numbers of that pull, and the fact that it’s the most horsepower Dahm has ever made on any of his projects.

Luckily, the only thing really on fire in this photo is the oil-soaked fiberglass mats. The engine was totally fine. The problem is the time it cost the team on the dyno.

“The engine survived not just at 7,500 rpm, but holding it there for an extended period,” says Dahm. “It was extremely rich, to the point where it was clearly misfiring. If we can repeat that run, pulling a lot of fuel out of the motor, the next run should have substantially higher numbers.” Unfortunately, that next run never occurred. While trying to clear out the flooded engine, they found that the crank trigger keyway had failed, leading to the disassembly of the front drive.

“The issue is that the engine flooded. It didn’t hydrolock, but it pushed some seals in,” explains a surprisingly upbeat Dahm. “I think there is some wobble in the E-shafts. Not that they are weak or anything like that, but that we need to look at some bearing support.” While the dyno test ended without the numbers Dahm expected, the engine still made more horsepower and torque than he or the engine ever had before.

With a couple of quick fixes, the next step for this insane engine isn’t to return to the dyno, but rather get fitted into its final home: the chassis of a dragster. There, Dahm will be able to really push the limits of the wild 12-rotor engine.

The final dyno graph from this 12-rotor engine. Obviously it needs to get cleaned up a bit, but Dahm ran out of time on the engine dyno. 1;515 horsepower and 1.281 lb-ft of torque ain’t too shabby. Dahm will get plenty of tuning time once it’s in the dragster and making passes.