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If you have followed Rob Dahm’s 12-rotor build at all, you know this thing is going to unleash all manner of hell unto the world. Apparently, the engine dyno owner was fully aware, which required some mini tests before the rotary could be rolled into the dyno cell. How much will it make? Dahm’s shop is just a mile or so from the dyno shop, so the first thing they did was strap the run stand down inside the trailer and take it to Vrbancic Bros Racing for the dyno session.
This engine is running a WOSP starter, which will spin the engine to 300 rpm. This has been a challenge in the past on this engine, and this new custom starter should do the trick. That isn’t the only issue, however. There are genuine concerns about this engine being able to safely be run in the dyno cell. Multiple intercoolers, all the piping, and so on, gave Bob Vrbancic, the dyno owner/operator, pause on even trying. The main concern is being able to reach every area of the engine in the event of a fire.
The dyno interface didn't’t match up to the flywheel of the 12-rotor so Rob had to run to the shop and whip up a little adapter ring. The ring spaces out the connection and allows everything to fit together. (left, center). Connecting the drive-by-wire pedal to the mechanical throttle on the dyno control panel took some effort but works flawlessly.
To rectify the issue, Dahm and his team got to work simplifying the arrangement, but there is an even bigger issue here: mounting the flywheel to the dyno itself. There is an interference issue, so Dahm needed to design an adapter ring to space out the hub so it would physically connect to the dyno. Mounting the engine to the dyno took hours, nearly the entire day.
The first two pulls were made N/A — engine only. The turbos made boost, but they were not connected to the engine intake. As the dyno load came in around 4,000 rpm, the engine went lean, so some more adjustments were made. The turbos are 94mm units, but while the Haltech ECM is set for boost to come in at 6,000, the turbos started making boost at around 4,000 rpm, an immediate sign that this thing is going to rip. The computer is controlling the boost, with all three banks of the engine getting roughly the same amount of air. In the initial runs, the engine’s fuel calculations appear to be correct, as well, with only one rotor falling out of the pack.
Connecting all of the plumbing from the engine to the dyno cell was no simple task. Once running, the engine started making boost at 4,000 rpm, which it isn’t supposed to do, and it went lean. Dahm adjusted the trims and changed the wastegate settings.
On the first day of testing, the Rob’s team made significant progress, including dyno testing the turbo 12 rotor, which produced over 750 lb-ft of torque at 3,500 rpm with the wastegate wide open and no boost. Those initial numbers are close to what the engine made with a carburetor, previously. However, a trip back to the shop was required to sort out some minor issues.
The starters are being damaged due to the high voltage, and Dahm’s team has used several alternatives, including a diesel starter, which had a different pitch gear with more teeth, making it incompatible with their current setup. Through multiple attempts, the starters just keep failing. The engine runs great, but starting it is the biggest issue.
WOSPerformance, an outfit out of the UK, built a custom-made starter that can handle the 24-volt starting system Dahm is using for the engine. This new starter uses a planetary gear-reduction system so the starter motor itself can be smaller. Additionally, Wosp can make custom offset gears if Dahm needs it. With the new starter, the team can move forward.
WOSP starters to the rescue, this new gear-reduction unit fits and should have the cheese to get this thing spinning. But, before the starter(s) can mount to the engine, the bellhousing needed machined to fit the new style starter mounts.
In order to get the new starter mounted, Rob machined the bellhousing and made an adapter plate so the starter could mount in the good location and not have any deflection or shift, as the previous mount allowed. The 12 rotor is set up for two (yes 2) starters. The goal for starting speed is 300 rpm. One starter at 12 volts spun the engine at 180 rpm, without spark plugs, which reduces the load. With both starters running at 12 volts, the engine spins at 215 rpm. However, one starter at 24 volts spins the engine at 316 rpm.
Wrapping up, the engine was tested with ethanol and without preheating the block, which is at a temperature of 60 degrees, making it a favorable scenario for the engine to work properly. The engine fires right up, almost instantly, which is an exciting moment. Unfortunately, this video ends without a full dyno run, which comes later. If you want a sneak peek, we’ll give you one- think well into four digits, and that whole concern over a fire? Yeah, that comes into play too.
