MR RICHARD T TRENK SR wrote:
> ---------------------
> Re. camshafts: I need your clarification on the term " l/C 108 " which
> puzzles. Tim posted a thought on this but that is not the answer, as cam
> grinders do NOT quote such a figure for lobe center to center. Reason being
> that the grinder MUST make the valves open and close in relationship to
> ONLY the crankshaft angles. No concern is made for the relationship
> between lobes nor is anyone interested in such a measurement.
>
Hi Richard,
I also wrote to you speculating that "L/C 108" was lobe center to lobe center. Not
wanting to disagree with you ... however I have seen lobe center to lobe center
specifications given for both small block chevy and volkswagen performance cams. If
one imagines a cam with a set of specific exhaust and intake characteristics (lift,
duration, and ramp up and down specs); then one could further imagine rotating the
intake and exhaust cams relative to each other. The closer they are rotated to each
other (ie: a lower lobe centerline to lobe centerline angle) the more overlap there is,
the less effective compression there will be at low RPM. High RPM cams tend to have a
lower lobe centerline to centerline angle. Conversely spreading the intake and exhaust
cams apart (higher centerline angle) results in less overlap, and the power band is
shifted lower in the RPM band.
Back in the '70s there was a choice of two factory chevy HI-PO cams. Both had
identical figures for lift, duration, takeup ramp, etc. The only difference between
the two was (as I recall) the lobe to lobe centerline angle. One of these cams was
referred to as "the 110". Of course these same information can also be conveyed as a
relation to chrankshaft degrees. It is just a different way of looking at the same
thing.
-Roger (and I am pleased that you continue to participate)
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