May 28, 2007 - Blower Assembly

The Merlin features a two stage centrifugal supercharger. Primarily designed by Sir Stanley Hooker and his team at Rolls-Royce in the 1930's and 40's, the design was truly revolutionary.

This engine will use a -7 supercharger, due to the quality and availability of parts. The main differences between a -7 and -9 blower are the method of fuel distribution (spray bar versus slinger ring) and diffuser design (-9 features a better constant area diffuser).

When assembling the blower, it is critical to have the appropriate clearance between the fans and their respective face plates. Too close and they rub (very bad) and too far apart and the efficiency drops (and thus does horsepower).

Boat racers have tightened up the clearances from stock values by shimming the rotors on the shaft.

To check second stage clearance, the shaft end play is used. For the first stage fan, clay is placed on the rotor and compressed when the hat is installed. When the hat is removed, the resulting thickness indicates the clearance.

Shims are adjusted until the clearance is within acceptable values.

Previous: May 19-27, 2007 - Banks & Intake Log
Next: June 1, 2007 - Completing Assembly

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