You can calculate advertised cam lift by multiplying the rocker arm ratio by the actual lift provided by the camshaft. Most engines use 1.5-to-1 ratio rocker arms. To get extra cam lift on an engine using 1.5-to-1 ratio rocker arms, install 1.6-to-1 ratio rocker arms. This trick will provide a power increase within the existing power band, where installing a higher lift cam with its associated increased duration would move the power band upward in the revolutions per minute (rpm) range, thereby providing an approximate 6 percent increase in lift. You must know your advertised lift value to calculate your new lift.
Record the advertised lift for your stock 1.5-to-1 ratio rockers.
Multiply that number by 1.067, which accounts for the difference between the 1.5-to-1 and 1.6-to-1 rocker arms.
Derive your new lift from the product of the two numbers. For instance, if your original lift is .45 inches, multiply .450 X 1.067 = .48015, which rounds off to .48, indicating a cam lift of .48 inches.
Tips & Warnings
- If you already have a big cam (over .45 inch), check your valve springs for "coil bind"---a condition in which the valve opens so far that the valve spring coils hit each other. (You will need a feeler gauge and the valve spring clearance specification for your specific engine to check for this condition.) If you encounter coil bind, you will need high-performance valve springs with thinner coils.
- Photo Credit IT Stock Free/Polka Dot/Getty Images
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