Speed Pro CS 118R

[Joe C.]

A friend of mine was good enough to provide me with lobe lift vs. cam angle data for the original GM 3849346 ("30-30") camshaft.

I measured lobe lift vs. cam angle from POML to the base circle of an inlet lobe from a CS118R that I have here, and compared the data to that from the original "346". I am happy to report that the correlation between the two is very close. The variance between the two @ POML has the Speed Pro showing .0008 more lift than the "346". This variance diminishes to zero at .0000 lobe lift, which occurs at the same point on both cams: 134 degrees, either direction (ie: opening and closing) from POML. There is a period of about thirty-five degrees (between 30 and 65 degrees from POML), on the opening side, where the CS118R maintains .002 - .007 more lift than the "346", and I doubt whether this would impact engine torque figures in any measurable way.

[Duke W.]

Re: Speed Pro CS 118R

IIRC the general tolerance on the drawing is +/- .002" at any given point with a maximum runnout rate of .00002" per cam degree.

The lobe is actually asymmetrical, but with very little difference at the very beginning/end of the clearance ramps.

On the opening side the last point of zero lift is 135 (cam) degrees before POML and 136 after POML on the closing side.

The L-72/LT-1 inlet lobe is much more assymetric.

The asymmetry is a bit more pronounced if you look at the tops of the .017" high clearance ramps - about 84.5 deg. before POML on the opening side and 87 deg. after POML on the closing side, so the actual seat duration is about 343 crank deg. The "SAE duration" (.006" valve lift) assuming a 1.5:1 rocker arm would be the .021" lift point, which is about 308 degrees. This .006" valve lift duration is what is usually quoted by aftermarket cam grinders as the "advertised duration".

The .050" lifter rise duration is 254 deg. but this includes the clearance ramps. The actual .050" lifter rise above the tops of the clearance ramps (.067") is 239 deg., which is the number you use to compare to hydraulic lifter cams. The L-79 .050" duration is 220 deg., which explains why the 30-30 cam is so weak down low.

The area you report that is slightly out of tolerance will likely have no effect on power or valve train dynamics. It's not that far out.

Duke

[John D.]

Re: Speed Pro CS 118R

Joe, As you have found out the CS118R is a good replacement for the 30-30. Several restoration shops I work for are using that cam with success. It appears to put out enough vacuum for the 64-65 FI's.

Too bad though the CS113R 097 cam is either history or hard to get from FM.

[Bill B.]

Re: Speed Pro CS 118R

Have you tried rockauto.com? or go right to the page here. http://www.rockauto.com/catalog/raca...&parttype=5260
SEALED POWER Part # CS113R {Performance Camshaft}
Performance Camshaft; w/high lift cam; Pro-5000 Perf. Cam; Mech., (050) Duration at .050 Lobe Lift, 230 Exh., 228 Int., 110 Degrees Lobe Separation, 0.401" Exh. Valve Lift, 0.395" Int. Valve Lift
$102.79

Bill

1961 Black/Silver/Red Int. 283/315 FI
power windows. Frame off 65% completed.
1989 White/hard top/Grey Int. daily driver 167,000 miles

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