The EC-630PP HMC - Haas - Haas Automation, Inc.

SIDEBAR
Rocker Arms 101
A rocker arm is the pivoting “seesaw” link
found between an engine’s camshaft and each
of its valves. These simple levers translate
rotary camshaft “data” into linear motion,
causing the valves to open and close at
precisely the right time.
Designing the rocker arm so its pivot point
(fulcrum) is closer to one end than the other
creates a mechanical advantage, which is
defined as the ratio between the two fulcrumto-tip
distances. Most standard small-block
engines use rocker arms designed with about a
1.5-to-1 ratio. In other words, each arm moves
its corresponding valve 1.5 times the distance
of the camshaft’s lobe lift.
High-performance rocker arms come in
significantly higher ratios: up to 2-to-1 for
NASCAR engines. By simply bolting on a set of
higher-ratio rockers, it’s possible to increase
valve lift by 7 to 10 percent, allowing the engine
to breathe better, and thus produce more
power. Specially designed high-lift camshafts
can do the same thing, but they’re more
expensive to manufacture, and much more
difficult to install.
In reality, many people who swap out rocker
arms have already changed the camshaft,
valves and springs in their engine. For these
enthusiasts, the rockers are just one part of the
puzzle – but a very important one.
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