Mailbag: Single Pattern vs. Dual Pattern Cams

You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re answering the basic question: What’s the difference between a single pattern and dual pattern camshaft?

K.B. Washington, PA

Q: What is the difference between a single pattern camshaft and a dual pattern camshaft, and how do I know when to use either pattern? Can you help?

A: A single pattern camshaft has the same lift and duration on the intake and exhaust lobes. This means the intake and exhaust profiles, or patterns, are the same. A dual pattern camshaft is essentially the opposite. The lift and duration on the intake lobes is not the same as the lift and duration found on the exhaust lobes. For instance, a dual pattern cam profile might offer 274-degree intake/288-degree exhaust duration at 0.050 inches of lift and a .719-inch intake/.690-inch exhaust lift.

Early factory camshafts were traditionally single pattern designs; however, it didn’t take hot rodders long to realize that poorly designed exhaust ports on stock cylinder heads could be improved by adding duration. This emphasis on the exhaust side led to the development of dual pattern camshafts, which aid in the scavenging of exhaust gases and help yield additional power. To this day, most untouched factory cylinder heads can benefit from a dual pattern camshaft, and even modified performance-oriented vehicles continue to enjoy increased power from dual pattern camshafts as well.

With the increased availability of well designed performance cylinder heads, single pattern camshafts have made somewhat of a comeback in recent years. In fact, improved aftermarket cylinder head designs offer such a strong balance between intake and exhaust sides that many builders are finding additional power by moving back to single pattern camshafts.