Why OHC?

["David A. Leonard" <dleonar1@xxxxxxxxxxxx>]

OHC is "better" because ther is much less moving mass in  the valve
actuating mechanism, and it is more rigid.  It allows much higher rpms with
less chance of valve float (valves not quite closing at high rpms).  It also
makes for an easy 4 valve per cylinder setup. It works well with a crossflow
head, wherein the intake manifold is in one side of the cylinder, and the
exhaust is on the other.  this helps with exhaust scavenging/reversion, and
allows for freer airflow..All these things translate to more power and
efficiency with smaller lighter engines.

Non OHC engines certainly still have their place, and work well for thier
intended application.  The American car guys started with "flat head"
configurations, where the valves were in the engine block, with the cam, and
the head was truly flat.  Sometime in the 1950's,  the manufacturers started
going to an OHV overhead valve configuration, with pushrods, and rocker
arms.  1955 wat the first year of the "small block Chevy"  an engine still
in production today, and one of my personal favorites.  Better breathing
through the OHV design allowed higher compression ratios, and higher power
to weigh ratios.  Overhead cam engines have been around at least as long, it
is just that they tended to be used in Europen high performance and race
engines...it took a while for the design to trickle down to the mass market.

I hope this answers your "Whats all this hoopla about Overhead cams"
question, without telling you more than you wanted to know.

Dave Leonard, Serious Motorhead

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