How can the
aftermarket valve-train industry possibly discover precision geometry, if one of
Detroit's gorillas doesn't apply it?
We've
used the example of Ford's 351C and 460 Ford engine for many
years, to explain how crazy it is to expect a relatively modest array of
engine builders, small companies (by comparison to Ford) and engineers
from the aftermarket, to foresee any need for "Precision Geometry" when
the likes of Ford Motor Company is going to take such a short cut as
they did in designing rocker arms for these two engines.
Ford's
460 engine has a pushrod geometry of approximately 18 degrees for the
intake, and 23 degrees for the exhaust (hence: 5 degrees variation). The
Ford's 351C
(Cleveland) has approximately an 8 degree pushrod geometry for the
intake, and 13 degrees for the exhaust. But...they use the same
rocker arm.
This
means if you take the two extremes of both engines, knowing that the
same rocker arm is going to be used for each, then you have a 15 degree
difference (8 degree Cleveland intake vs. 23 degree exhaust of the 460).
The rocker is only going to rotate 22 degrees, yet it is off by 15
degrees for one extreme or the other, for the engine builder to choose
on setting up his installed geometry!
With this
said, how in the world can you expect weekend warriors building cam and
rocker arm companies for the aftermarket industry, to presume to know
more than Ford Motor Company on what is "needed" for precision geometry?
With such loose precedents floating around, from one of the world's most
resourceful automotive engineering companies, it's no wonder why rocker
geometry among established cam and rocker companies has not been treated
very seriously. There simply was "no standard" to follow! Not
even Ford.
