Not me!
What's going on there - the stems flexing above the guides (as seems to be suggested) or the entire valve moving in the guide? And why?
Given the working clearances between the I.D. of the valve guide and the
O.D. of the valve stem, we're seeing too much movement for it to be that.
I think that what we're seeing is the stems forced into oscillation above the
guides by the ginormous valve springs?
You know, if you go back 30 years & read about the spring pressures in
use for the flat tappet cams of the day vs. the spring pressures
that are being used today to try to control the heavy roller lifters
on today's cam lobes with such aggressive ramps, we are now
running a lot stronger springs. But at the same time the valve
stem diameters have remained the same?
People also don't realize that when you spec out something
like a Comp Cams
XE282, the
XE stands for "e
Xtreme
Energy",
and if you read around about this cam series the tradeoff between
max performance vs. max reliabiilty favors the former.
One thing to keep in mind is that with a DOHC design
the cam follower is in direct control by the valve spring.
But on our pushrod motors, the part with the most
mass is the lifter, and that's at the far end of a pushrod,
which in turn goes through a 1.5:1 ratio rocker arm
before we get to the actual valve spring. That means
that the weight of the lifter is actually multiplied by a
factor of 1.5x!
But the folks who are forced by competition (and/or
love for the siren song of a V8 being run way upstairs)
will solve this lifter control issue by adding an
additional set of springs in parallel to the original
valve springs. (The pushrod still couples the
valve
spring tension into the center of the lifter, while
the
rev kit springs are coupled via the outer
diameter of the lifter.) Hard to explain w/words,
much easier to see in this SBC photo:
SBC 'Rev Kit' installed in the lifter valley, pushing directly on the lifter bodies.
You must be registered for see images attach
(credit: 'offshoreonly' website)
The math gets messy & my noggin bogs trying to
understand it all (much less explain it) ...but common
sense would dictate that in order to control
everything
from a distance (from breaking into oscillation) you
will have to run a higher spring pressure -- as opposed
to having 2 sets of valve springs working in parallel, each
set of springs directly connected/optimized to the task at hand.
The drawbacks are obvious -- mo' money + extra
aggravation during maintenance. But if your plan it to
build a max-effort motor, but run it at, say, 80-85% of
max rpm (so that it lasts a full season+) ...then the
maintenance drawback is essentially nil.
Maybe with a rev kit your valve stems
won't be oscillating
due to being forced to install a gigantic spring kit
only at the
valves in order to maintain control over the whole shebang?
Who knows? Maybe taking some reactive stress out of
the vicinity of the valve itself will help prevent dropping
of said valve? (Similar to the divide & conquer approach
to the stresses put on a full-floating
axle vs. the same axle in a conventional diff?)
Sometimes, too much brute force in one area is
simply not as reliable as 2 lesser forces distributed
through the mechanical circuit?
(BTW, I don't claim to know the answer...but I do
enjoy sharing some food for thought like the above.)
****
Bottom line, there's no free lunch in any area of our
modern engines, especially in the valve train.
PS: Since those beehive valvesprings don't have a
single resonant frequency, they really are a worthy
upgrade to the 383 that is sitting under the
stamped steel Chevrolet-scripted 283 valve covers in your
sleeper. :0)
Be careful what you buy & how hard you twist it,
for dropping a valve is a $,$$$+ proposition.
Cheers --
