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Harley Davidson bobbers worth blogging about, plus a few yamaha and triumphs

September 24, 2011

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honda xr250 by low brow customs

History of the harley Davidson sportster

when old is new again

Researching the air-cooled Honda XR650 L engine I came across the acronym RVFC cast into the valve head. RVFC or Radial Four Valve Combustion was a proprietary valve arrangement created by Honda to make a four valve head flow more like a hemi head. Honda RVFC or Radial Four Valve Combustion, splays the valves radially away from the bore's axis and creating a hemispherical combustion chamber when viewed from the engine's profile. The splayed valves arrangement allows quicker flame propagation across the combustion chamber, allowing the engine to produce more power at a given RPM. Additional benefits include better cooling and the engine's timing can be more radically advanced. MV Agusta's new 750cc inline-four uses a radial valve configuration because the engine utilizes a small stroke relative to its bore. A smaller stroke will allow an engine to rev to higher RPMs and produce large amounts of horsepower but when we reduce an engine's stroke it will produce l

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