I'm no expert but here is my understanding;
The 210/220 @ 0.050" numbers are the degrees of CRANK SHAFT rotation (out of
360) that the valves is open 0.050" or more. The actual duration from the
instant the valve opens to the instant it closes is much larger. The degrees at
0.050" has become a defacto standard way of measuring duration that allows you
to compare cams between manufacturers. In general terms more duration enhances
high rpm power at the expense of low rpm power.
LSA is the degrees of CAM SHAFT rotation between the center line of the intake
lob and center line of the exhaust lobe. In general terms more LSA increases
low rpm power and also increase idle vacuum, less LSA is just the opposite.
The centerline is the number of CRANK SHAFT degrees after Top Dead Center of
the highest lift point of the Intake lobe. Advancing the cam (having the valve
open sooner) from 108 degrees to 106 degrees enhances low rpm power at the cost
of high rpm power and retarding the cam is the opposite. Most cams when
installed straight up (that is, lined up the timing marks) are installed 4
degrees advanced. Before fiddling with offset keyways make sure you understand
where the cam is.
The one thing you didn't mention is degreeing in the cam. That is basically
actually measuring the cam events and making sure they are happening when they
are supposed to. It is not unusual for timing marks to be off (or the cam to be
ground wrong) resulting in the cam not being set up where the manufacturer
intended.
Dave Clement
99 SLT+ CC 4x4
In article <200411150014.iAF0E2Zo017179@ms-smtp-02.tampabay.rr.com>,
jCalder3@cfl.rr.com ("James Calder") writes:
>
>
> All right, I really need to better understand cam specs. I have a basic
> understanding but I'm sure there some things I just assume in my thinking.
> Maybe someone can clarify these specs for me (I'll use a Comp Cam 604 as an
> example):
>
> Duration @.050 210/220 : I know 210 is intake and 220 is exhaust.
> 210 degrees of what?
> Is it 210 degrees out of 360?
> 220 degrees of what?
> @.050 = ?
>
> LSA Lobe Separation Angle 112 degrees:
> That would be the distance between the top of the intake and exhaust lobe,
> which controls the how much time is between the opening and closing of the
> valves?
> Is that what causes overlap and a lumpy idle?
> How is performance affected when the LSA is changed in a cam (going from 112
> to 108)?
>
> Lift:
> That one is pretty straight forward.
>
> Centerline installation:
> I read a cam can be advanced or retarded depending on what centerline it's
> installed on. My 604 is installed on a 108 degree centerline. How would a
> 106 centerline affect performance? How about a 110 centerline?
>
> Thanks all!
> James
>
>
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