I'm confused with cams

[graham.hilder@xxxxxxxxxxxxx (Graham Hilder)]

In no.185, Tom wrote about those 11Ps performance cams,
describing how changing their timing from the specified 110
degrees to say 102 degrees would improve the low-end torque at
the expense of some high-end preformance.   This agrees with
what's written elsewhere of course, but I get confused if I try and
relate these figures to the degrees of overlap.

 It seems to me that bringing the lobe centres closer together, e.g.
going to 102 degrees from the standard 110,  would increase the
overlap, and I gathered that more overlap would decrease the
low-end torque rather than increase it.  Clearly I've got something
wrong here, either in the cam timing sketches I made, or in my
understanding of overlap and its effects. Would someone like to
straighten out my thinking please ?   This matter has puzzled me
often.

(I worked out that the 110 deg timing would give 60 degrees
overlap, and the 102 deg timing would give 76 degrees overlap,
given the 280 degree durations.  Where am I going wrong do you
think ?)

Thanks all,
Graham Hilder,
N.Z.

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