Mid-Lift? Now that's odd. When you're building an engine
with new and different heads, different rocker arms, or different
valve stem lenghts, etc, what you do is put lightweight springs under
the retainers of one intake and one exhaust valve then use adjustable
push rods to adjust the rockers (by turning the engine over and
adjusting the push rods), so the roller tips of the rockers transition
across the valve stem an equal amount on either side of the valve
centerline from closed to fully open position. You also check for
cleance problems between the retainer and the rocker arm, and the push
rod and the head or guide plate throughout it's travel . When you've
adjusted your intake and exhaust pushrods to achieve that condition,
you order some non-adjustable pushrods of the same or similar length.
Doing it that way there is no Over-arching or Under-
arching, and any roller tip rocker arms are essentially "Mid-Lift"
Let me add that this procedure is for stud mounted rocker arms like
Big and Small block Chevies use. Shaft mounted rockers don't have as
much adjustment leeway, without milling or shimming the rocker shaft
I was just giving you an alternate perspective on rocker arm Over &
Under arching. And how do you KNOW that rockers other than Mid-Lift
rockers are necessarily designed improperly?
If the article was inaccurate about Over and Under arching, then that
calls into question some of their other assertions.
These seem to be just forum members speculating on the pros and cons
of rocker arm geometry. A lot of those posts remind me of the 10 blind
men describing an elephant. Each one has a piece of the truth.
Is "Mid-Lift" a better method for measuring installed rocker geometry?
Do "Mid-Lift" rockers make more power? I haven't seen any data to
support OR refute such a claim.
You sure jumped off on a tangent there. Do you fancy yourself the
"Jim Miller" of CAD/CAM?
Is someone going to financially back this test, or would Joe Sherman
have to eat it himself? If the latter, there would not be much
incentive for him to do it.
There seems to be a power play & finger pointing situation going
between parties with invested interests on with this issue.
There are a lot of variables to take into consideration, early valve
acceleration, late acceleration, and how it affects the "area under the
curve", valve bounce due to high closing accelerations,
advancing/retarding the cam to take advantage of the various rocker
designs and ratio changes during operation, with charge/port velocity
capabilities thrown into the mix as well, to say nothing of valve train
harmonics & stability. Remember, in a V8 running at 8,000 RPM a valve
is opening and closing some 66 times per SECOND. A lot is happening in
a short period of time, so small changes can have drastic effects.
Then you possibly have racers that may not wish to give out ALL their
HP building secretes for fear of losing their competitive EDGE.
At least you TOTALLY haven't lost your sense of humor.
Agree, there wouldn't. He's after higher horsepower gains. I think
it's all he cares about.
Isn't this almost always the case?
Joe's edge is years and years of trial and error at the expense of a
more in depth understanding. Typical race engine builder. Mid-Lift
might make his engines last longer and that's something I don't think
Joe really cares about.
I expect much less from people now and I'm frequently rewarded with
what I expect.
San Diego, CA