Specifications
- 300-cc Roots blower
- Wet, after carburetor
- Belt-driven, variable boost with multiple driven pulley sizes
Jump to: [Install] [Tuning] [Starting Motor]
Install
The supercharger itself sits atop the intake manifold, between the V-twin cylinders (yellow arrow in picture). It is mounted to the motorcycle frame rather than the engine, simplifying access to the engine for maintenance without disturbing the supercharger. The crankshaft drives the supercharger using a pulley and belt system (under black case).
The OEM dynamo and starter assembly were removed in order to attach the supercharger drive pulley to the crankshaft. The steel hub from the dynamo and starter assembly was modified to attach a 2-kg custom-machined 4140 steel flywheel. The flywheel is drilled and threaded to attach a Gilmer pulley which then drives the supercharger through a belt.
Tuning
Modifying the Moto Morini to include a supercharger has not been simple. The supercharger increases the demand for air, fuel, and spark as well as thermal management and lubrication. Superchargers require a compromise between increasing boost pressure while limiting compression heating of the intake air and friction drag from spinning the supercharger.
Air-Fuel Ratio
The supercharger is located after the carburetor. With this configuration, The Red Baron runs a 10.5:1 air-fuel ratio. The rich AF mixture cools the supercharger and increases the evaporative cooling of the pressurized intake charge. A cooler intake charge is denser and will produce more power.
Variable Boost Pressure
The Red Baron is supercharged to achieve an intake manifold pressure of 54 inHg, which is considered the upper limit for a supercharged air-cooled engine. The desired boost pressure is based on the ambient pressure of the race location like El Mirage Dry Lake (2,900′) and the Bonneville Salt Flats (4,200′). Multiple driven pulleys of different sizes allow for selecting the appropriate blower speed and boost pressure.
Compression Ratio
The compression ratio was dropped from 11:1 to 8.6:1 to maintain reasonable peak cylinder pressures with the now-supercharged engine. Thinner head gaskets can be used to increase the compression ratio in small increments until thermal management becomes an issue.
Starting Motor
Since the supercharger was installed in the place of the starter assembly, The Red Baron is now started by spinning the rear tire with an auxiliary starting motor. The starting motor back-drives the transmission in 3rd gear, generating oil pressure before powering the ignition system.
