The dyno graph below shows a 900SS carb model fitted with hi comp pistons as opposed to a std piston bike. Both bikes are fitted with after market mufflers, but otherwise are standard. As you can see, the hi comp pistons certainly make a difference. These give a nominal compression ratio of 10.5 : 1, with the std bike quoted as 9.5 : 1. Also included in this mod is an adjustment ( retarding ) of the ignition timing, as the std settings cause the engine to ping like crazy on normal unleaded, and just a little on good high octane fuel. We will hopefully get to do the usual cam and carb mods on this bike also, so it will really go.

The graph is shown below. The hi comp bike is red, the std comp bike green. Very nice improvement.

(dyno graph courtesy of DYNOBIKE, (03) 9553 0018)

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