Duration is how long the valve is off its seat. It is listed in degrees of crankshaft rotation. When someone refers to a “big cam,” they mean it has longer duration, not higher Lift.

What is a good camshaft duration?

A 280-degree-duration cam holds the valves open longer than a 260-degree-duration cam. Holding the valves open longer allows more air and fuel into the engine and also allows more to get out through the exhaust. Longer duration (higher number) improves top-end power but almost always sacrifices low-end torque.

How is camshaft duration measured?

Camshaft Duration is the measurement of the time one valve begins to open until it finishes closing. Duration is measured in degrees of crankshaft rotation, not camshaft rotation. You’ll see duration specifications at . 050 inches.

How does cam duration affect torque?

Duration has a marked affect on the cams power band and drivability. Higher durations increase the top-end at the expense of the low end. As a general rule, cams with 220-235 degrees of duration tend to produce good low end torque.

Which is better more lift or more duration?

Designing a cam profile with more lift results in increased duration in the high-lift regions where cylinder heads flow the most air. Short duration cams with relatively high valve lift can provide excellent responsiveness, great torque, and good power. But high lift cams are less dependable.

How do you choose cam duration?

However, if you want to find the duration for the camshaft in your engine, you can calculate it.
Using a Dial Indicator and Degree Wheel, find the opening and closing points of the valves at 0.050 in. of lift. If the intake valve opens AFTER TDC, use a negative value. Add the numbers together.Add 180° to find duration.

How do I know what camshaft to buy?

The rpm range is the range where the engine performs best. When selecting a camshaft, choose one with an rpm range that matches the other components of your vehicle and its intended use. Follow this link for more about Basic Operating RPM Range.

What do the numbers mean on camshafts?

The first two numbers are the degrees of opening being 210 for the intake and 218 degrees for the exhaust given normally at .050 inch of lift. The next two numbers are the valve lift of intake and exhaust in thousands of an inch. The final number is the degrees of overlap.

How do I know what size my cam is?

Take your digital caliper and measure the smallest diameter on the cam. This is called the base circle. This cam measured at 1.10 inches and 87 thousandths. The next value you will need is the largest diameter on the cam, the lobe part, which is called the base circle and lobe lift.

What does a mild cam mean?

In general, a stock replacement camshaft with duration of less than 200 degrees will have a lobe separation angle of more than 114 degrees. An RV or towing camshaft, which is considered a mild performance or an economy cam, will often have a narrower LSA, between 112 and 114 degrees.

Does cam duration affect idle?

Again, keeping all else constant, more duration will make the engine less efficient at low rpm, with more overlap dilution of the induction charge, and the later intake valve closing reducing the trapping efficiency. Therefore, a long-duration cam will cause rough running at idle (lope) and a loss of low-rpm torque.

Do camshafts increase rpm?

Generally, cams with smaller duration numbers make peak horsepower at lower rpm. These cams are often used for stock replacement, daily driver, and towing applications. As you increase the duration, you increase the peak power the engine can make. However, you also move the power curve higher in the rpm range.

What is camshaft lift and duration?

Lift and duration are the primary factors that determine a cam’s profile. Lift is the amount a cam lobe actually moves a valve off its seat and is measured in fractions of an inch. Duration is the amount of time a cam keeps a valve off of its seat, measured in degrees of crank rotation.

What is considered a lot of cam overlap?

To maintain sufficient idle and vacuum qualities, the cam tech recommends the cam be ground on, say, 112-degree LCA, which gives an overlap of 66 degrees. For a typical performance-headed 350, the optimal LCA is usually 108 degrees.

Do camshafts increase compression?

Overlap causes a “scavenging effect” as the engine RPM increases. This is why performance cams “come alive” at higher RPMs. It’s not “just” the cam making the power, it’s the cam’s scavenging effect working as the RPM increases which increases cylinder pressure (dynamic or effective compression).

What is the difference between a Stage 1 and Stage 2 camshaft?

Most Stage 1 type modifications are typically in the +10-15% power increase over stock. Stage 2: this is typically referred to an engine with a performance cam upgrade as well as the other components within a Stage 1 combination. A typical Stage 2 has generally +20-25% more HP than stock.

How do you match a head with a camshaft?

Typically, a head with a high percentage can use a cam with more closely matched intake and exhaust lobe figures. Conversely, a head with a poor ratio between the intake and exhaust flow will benefit from more exhaust duration to evacuate the burned gases.

What is a good camshaft brand?

According to our BrandZoom™ Camshafts report, based on surveys of automotive enthusiasts who have shopped for or purchased a cam, the top 3 camshaft brands that are most trusted are COMP Cams, Crower and Edelbrock (in alphabetical order). Each of these three had a 90% or higher positive perception.