It isn’t always obvious which camshaft we should choose for our engine build.

Even when we fully understand the individual timing events and how each of them interact in a four-stroke engine’s piston and valve motion, the complexity of it all can bring confusion and uncertainty to the cam selection process.

We just learned about a new tool that pretty much eliminates the confusion and uncertainty, courtesy of our friends at Summit Racing, and their partners in developing it—the cam experts at Cam Motion.

That new tool—your new secret weapon—is the new Summit Racing Cam Timing Calculator.

screenshot - cam timing calculator

(Image/Summit Racing)

How the Cam Timing Calculator Works

The Summit Racing Cam Timing Calculator does two things:

  1. It converts duration, lobe separation, and advance into the four individual timing events that will ultimately dictate engine performance.
  2. It also works the opposite way. You can tweak any of the four events in the calculator to learn what the resulting duration, lobe separation, and advance would be under the new conditions.

No matter what engine or application you’re building it for, you can quickly compare specs and how they differ under different running conditions.

For examples, check out this video:

[NOTE: Looking for the Summit Racing Cam Timing Calculator? Find it and several other helpful calculators and tools to help you determine compression ratio, gear ratio, CFM requirements, and more on Summit Racing’s Calculators and Tools page.]

Understanding the 4 Key Individual Timing Events for Camshaft Selection

Let’s back up for a minute.

In previous articles, we’ve talked about the importance of Considering Individual Timing Events When Choosing a Cam to help us determine the duration, lobe separation and advance needed. This is especially important for cars with electronic injection which are dependent on idle vacuum to run correctly.

Here’s a quick recap of the four events in order of importance:

1. Intake Valve Closing (IVC)

This event has the most control over the powerband. We trade low-end torque for high-end horsepower when we close the intake valve later after BDC.

2. Intake Valve Opening (IVO)

This is the first component in overlap and the most important to idle quality. The idle gets rougher when we open the valve earlier BTDC, but we net more airflow on the intake stroke.

3. Exhaust Valve Closing (EVC)

This is the second component in overlap and is a compromise between reversion at low rpm and part throttle and the positive effects of scavenging higher in the power band and WOT.

4. Exhaust Valve Opening (EVO)

This is the least critical of the four events due to high residual cylinder pressure blasting out of the cylinder even before the piston hits BDC. It helps rid the cylinder of burnt gasses, but it’s a compromise. Opening too early before BDC decreases pressure on the piston that could be used to turn the crank, but reduces pumping losses. Pumping losses are caused by pressure working against the piston when it’s on the upstroke after BDC.

For a better understanding of the how’s and why’s behind tweaking individual valve events, check out this video which will help guide you on the path to mastering cam timing.

Author: Brian Nutter

After a stint in the U.S. Air Force, Brian Nutter studied at the Houston, TX-based School of Automotive Machinists in 1997. The early part of his automotive career included working for engine builders Scott Shafiroff and C.J. Batten, followed by several years developing performance pistons at Wiseco Piston Co. Today, Brian develops performance parts for Summit Racing Equipment and is a regular OnAllCylinders contributor. For fun, he runs his 427-powered C5 Z06 in ECTA land-speed racing, at OPTIMA® street car events, and at a mix of autocross, drag racing, and track days.