DYNO-PROVEN
`We've tested a lot of cam and valvetrain components in the past few years and have decided to give you an education by reviewing some of the more interesting results we've found and condense it into data you can use for your next engine project. The best way to approach this story is to not get up in the fact that most of these tests were performed on a small-block Chevy. Instead, see what trends you can pick up from the testing and then apply these same concepts to your next engine. After all, the engine doesn't know what logo is stamped on the valve cover.
Degreeing a Cam
If you've read more than two engine-buildup stories in your lifetime, then you've no doubt been exposed to the concept of degreeing the camshaft. The cam companies emphasize this process so the builder knows that the camshaft is properly phased with the engine. Why this is important is the subject of a Marlan Davis test from the February '98 issue where he performed a series of three tests on the same engine on Flowmaster's Superflow dyno in which the only variable was to advance or retard the camshaft. The test was designed to look at actual power numbers to verify the theory of advancing and retarding cam timing.
The test was performed on a (what else?) small-block Chevy, but the results would be reinforced with almost any engine configuration. They pretty much followed the theory that advancing the camshaft improved bottom-end torque, while retarding the cam from the zero or "straight up" position hurts bottom-end power while slightly improving power at higher engine speeds. One thing to keep in mind is that many cam manufacturers build in a certain amount of advance when grinding the camshaft.
Degreeing the cam merely means ensuring the camshaft is in the proper position relative to the rest of the engine. This is normally expressed in relationship to the No. 1 piston or as an intake centerline number. |  |
This particular Crane cam uses a recommended intake centerline of 108 degrees while the lobe separation angle (LSA) is 110 degrees. This means the cam is actually ground with 2 degrees of advance built in. A cam ground with zero advance will always have an intake centerline equal to the LSA, which in this case is 110 degrees. This cam actually uses an intake centerline of 108 and an exhaust centerline of 112 degrees for an LSA of 110 degrees (108 + 112 = 220/2 = 110 degrees). Advancing the cam further in this case did not improve overall power compared to the zero baseline, although it did pump up the torque down low. The point of all this is that you should be aware of what the cam companies are doing before you decide to make changes. In most street cam examples, that advance has already been done for you. Advancing or retarding a camshaft affects all of the opening and closing points for both the intake and exhaust lobes. Since intake closing is the most important of these four points, advancing the cam closes the intake sooner to improve low-speed power while retarding the cam closes the intake valve later, which improves top-end power.
Cam Specs Duration DurationDescription (Adv.) (@ 0.050)
Lift LSACraneIntake 284 222 0.480 in 110Exhaust
292 230 0.496 in
Power Chart Average HPRPM 4 Adv. 0 4
Ret.2,000 127 124 1212,500 163 161 1553,000
229 227 2233,500 271 270 2664,000 311 310
3064,500 340 340 3405,000 365 366 3635,500
386 388 3866,000 381 391 392
Avg thru 4,000 220.4
218.2 213.7Avg. 4,200-plus 365.9 368.2 368.4Avg. overall 293.2
293.2 291.1
Adv Ret Zero 4 Deg. 4 Deg.Intake lobe
centerline 108 104 112Exhaust lobe centerline 112 116
108