I purchased a used hydraulic roller camshaft from a friend that was originally used in an LS1 engine. My buddy says it’s a mild cam that’s bigger than a stock LS6 version, but he didn’t have any more information. The end of the cam is stamped 3709/3711 HR 114 followed by CC and 7661-11. Can you tell me the specs on this cam from these numbers? On other cams I’ve looked at, they just list the part number – which is easy to look up, but this cam has a bunch of numbers I don’t recognize.

D.S.

thumpr-camshaft-group-421w-219hJeff Smith: First of all, the CC refers to COMP Cams. That gives us our first clue where to look for the rest of the numbers. If we didn’t already know this was an LS cam, the first thing we would want to do is determine the engine family. COMP Cams uses two-number designations for all its engine families. The LS engine is designated 54 and this number is generally the first two numbers that define the actual cam part number. Other examples include small block Chevys -12, big block Chevys -11, and 5.0L small block Fords -35.

The 3709/3711 numbers are references to lobe designs. Each family of cam lobes has its own numerical designation with the same basic configuration, usually encompassing multiple individual durations that also might include changes in lobe lift. To decipher these codes, we accessed COMP’s website at compcams.com. On the home page, we looked for the “Information” tab and then clicked on “Catalogs”. Under that heading toward the bottom we found a tab for the Cam Lobe Master Catalog. This is the COMP Cams equivalent of the Rosetta stone for cam lobes.

In the catalog, you will see the cams listed by configuration starting with flat tappet hydraulics and then hydraulic rollers–which is what we want. Once we found the hydraulic roller section, the first column lists each lobe by number. We continued down the list until we found the 3709 number, which because it is listed first on the camshaft, is the intake lobe. We found it under the heading of Xtreme RPM for LS1 lobes, Hi Lift.

The 3709 lobe is listed as 265 degrees of advertised duration with 212 degrees at 0.050 and 0.328-inch lobe lift. The lobes are also listed with various theoretical valve lifts–the one we’re interested in would be the LS1’s 1.7:1 rocker ratio that delivers 0.558-inch of lift. All you have to do to determine valve lift is multiply the lobe lift times the rocker ratio. With this intake lobe: 0.328 x 1.7 = 0.5576-inch, which COMP rounds off to 0.558-inch. The second lobe number 3711 refers to the same family of lobes–this one spec’d at 269 degrees advertised with 216 degrees at 0.050-inch tappet lift with a lobe lift of 0.330 and a theoretical valve lift of 0.561-inch.

The next information engraved on the cam was HR 114. The HR refers to this as a hydraulic roller camshaft while the 114 refers to the lobe separation angle (LSA). When referring to LSA’s, the larger the number, the more degrees of separation between the intake and exhaust lobes. The greater number of degrees means there is less overlap between the intake and exhaust lobes. If the number was 110 degrees, this would increase the amount of overlap. Less overlap generally produces a more stable idle while more overlap makes the idle lumpier. Stock GM LS engine cams feature LSA anywhere from 116 to 121 degrees because GM is concerned with creating a very smooth idle. But this comes at the cost of reduced torque in the middle of the rpm band.

The only thing we don’t know from these number is the cam’s intake centerline. We have a hint because if a camshaft if ground with no added advance, the intake lobe centerline will be the same number as the LSA–114 degrees After Top Dead Center (ATDC). However, most cams intended for street use are ground with several degrees of advance. This advances the intake centerline by that number of degrees. We investigated a couple of our Comp off-the-shelf LS cams and found they were ground with 5 degrees of advance, but that is no guarantee that your camshaft is ground that way. The 7661-11 is a serial number specific to that camshaft only.

We compared these specs to the catalog and because there is no list number on the end of the cam, we will assume this was a custom-ground camshaft. COMP offers this  as a service to anyone who is looking for a custom combination of specs that are not listed as an “on-the-shelf” cam. This requires a little more time but COMP does not charge extra, which is a great service if you are into tweaking the cam a bit to do something special.

If you want to know where the intake centerline is located, all you have to do is install the cam in the engine and then degree the cam. Some enthusiasts just compare the opening and closing points of the intake with the cam card but this isn’t as reliable as the intake centerline method. In this case, we don’t know what the opening and closing points are – although you could compare the intake lobe points to an off-the-shelf XFI RPM Hi-Lift cam and probably be pretty close.

For the intake centerline method, once the cam is installed and TDC is established on the degree wheel, then roll the cam around until the dial indicator signals maximum lift. Now zero the indicator and turn the engine backward until the dial indicator reads roughly 0.100-inch. Now turn the engine clockwise and stop at 0.050 on the opening side of max lift and record the degree wheel reading. Then do the same process with the lobe at 0.050 on the closing side. Add the two numbers together and divide by 2. This will give you the intake centerline. With your cam it might come out to somewhere between 114 to 110 degrees depending on if the cam was machined with advance.

Hope we’ve helped you with a little more camshaft knowledge. For as simple as this product appears, it is actually a very complicated piece of engineering if you study it closely.

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Ask Away, Camshafts, Jeff Smith
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.