2nd Update: Engine developer Tyson Gavin has posted a pair of videos of the 12-rotor engine making its initial dyno runs. We featuring the short version above while the long version can be found on the bottom of the page. There’s action of the engine during break-in and mild pulls. As noted before, the team is working on a full EFI system to provide enough fuel for the 960ci engine. A single Holley used for the startup just isn’t providing enough juice. The latest videos provide clearer audio of the 12-rotor bullet and give a healthy hint of what’s to come in the near future.
Update: The official Facebook page for the R12 12-rotor rotary engine just posted power numbers from the engine’s first dyno session, and they’re quite compelling, to say the least. The best run posted 815 lb-ft of torque at just 3,200 rpm. Owner Tyson Gavin says in the FB post that he engine has been run to 7,500 rpm but only under part throttle as getting enough fuel and air to the 960 cubic inches of displacement has been a challenge. A single 1,300 cfm carb is currently the only induction source while the team awaits a full EFI system. They tried adding two more carbs but the extension killed the vacuum signals from the engine. They even added a nitrous plate to pump in more fuel. Gavin says the engine will be inspected and then fitted with the EFI system before testing continues.
This wicked-looking 12-rotor rotary engine has been seen a public a few times in the past couple years, including PRI, but hasn’t made much noise until recently.
Tyson Gavin, designer of this unique tri-bank engine, posted the above YouTube video of the engine starting for an initial set of shakedown tests to check for leaks, sealing, oil pressure and so on. The next step is bolting it to a dyno and making pulls to dial in the EFI and spark tuning, and then it’s time to make the power pulls.
A record-holding boat racer, Gavin started work on this engine design almost five years ago to develop an alternative to traditional marine performance.
“We came to the limit what a big-block could,” says Gavin. “We wanted to make more continuous power, not just power for drag racing. The rotary makes more power for its size.”
Gavin measured up a fully dressed marinized big-block Chevy and concluded that 12 rotors would neatly fill that space. Overall, the 12-rotor engine is 30 inches long, 31 inches wide and 24 inches tall. Total weight is 830 pounds.
Gear arrangement includes an idler gear to allow the right two banks to turn the same direction while the top left bank is counter rotating.
“We looked at a 100 different ways to [arrange the rotors],” he remembers. “But [Y design] was the only way get 12 rotors in the space of a big-block.”
Basically, there are three banks of four rotors. The top two banks help drive the bottom bank that has the actual output shaft. The three banks are connected by a gears on the back of the engine block. One bank is set up to counter rotate against the main bank while the other gearset is fitted with a idler gear so it rotates in the same direction as the main shaft.
“We needed one bank to counter rotate so the exhaust side would match up with the other,” says Gavin.
With the exhaust ports facing in the same direction, it will be easier to equip the engine with turbos. The intake side, however, requires a unique manifold with a common plenum and 12 runners that snake their way down to the intake ports. Although a carb is used on the initial startup tests, the intake is equipped with individual fuel injectors positioned inside the plentum above the intake runners. The injectors, along with the 2-spark-plug-per-rotor-ignition, will be controlled with an Adaptronic ECU.
All of the design work and machining were handled in-house by Gavin and his team. The rotor size is about the only common denominator with a traditional Mazda rotary engine. With the 12 rotors, displacement measures 960 cubic inches. Once the basic design was determined, the team had to finalize details such as coolant passages, sealing and oil galleys. The rear of the engine is set up with a BBC bellhousing bolt pattern — again, with the goal of replacing big-block Chevys already installed in performance boats. The output shaft even has the same spacing and flange as a BBC crankshaft. All totaled, there are only 19 moving parts in the 12-rotor engine, which should improve durability.
According to Gavin, the engine is designed to be flexible enough to use in pleasure boating at around 1,400 horsepower for up 400 hours between scheduled maintenance, or it could be turborcharged with a pair of 122mm turbos (10 pounds of boost) to make 2,400 horsepower for about 200 hours for poker runs and other spirited adventures. Both those power numbers are on 87 octane fuel. Jumping up to 25 pounds of boost on race gas could elevate the power levels beyond 3,600 horsepower. And 50 pounds of boost could result in over 5,000 horsepower. For steady state running, recommended rpm will be in the 8,500 to 9,000 range. But an all-out drag version could spin up to 14,000 rpm.
“These numbers come from a 2-rotor version we built and dynoed,” says Gavin. “We’ll start off with two turbos. If they don’t supply enough air, we’ll add two more.”
The modular design of the engine allows a variety of configurations, including diesel and a 6-rotor version.