Choosing the right cam

In order to determine what camshaft to use, the basics are as follows;

1- Determine the use of the car. Be as honest with yourself as possible. What you see yourself doing with the car, vs. what you'd like to do with the car can sometimes be different scenarios.

2- Determine a goal HP/TQ number range that will achieve #1.

3- Build the drivetrain together. If this means you are leaving parts of the drivetrain the way they are, know what you have, even if it requires a little tear down. The more you know, the better you will be able to tune and build the engine to suit the parts within the drivetrain that will end up in the car.


Once you have those ideas squared away, approach the geometry of the camshaft with understanding it's effect on the valvetrain. Rather than thinking about numbers, think about what each operation of the cam performs.

The engine goes through four cycles.
1- Intake valve opens and chases the piston down, allowing the engine to draw in air
-intake valve closes
2-Piston compresses the gas
-both valves are closed
3-Spark ignites compressed gas and forces the piston down
-exhaust valve opens
4- Exhaust valve is open, piston chases exhaust valve until it is shut
-exhaust and intake valve are both slightly open for a short duration, during exhaust closing and intake opening again.

Effects of each geometry on the running cycle-

Lift is equal to the volume of gas allowed into the chamber, static (static, meaning frozen in time, ie. not taking flow into consideration yet)

Duration is equal to the amount of time that gas is allowed into the chamber, taking static lift and giving it the dimension of time for operation.

Lobe separation angle is the measurement between centerlines on intake and exhaust lobes for the same cylinder. This has a direct effect on the overlap within the cycle that RatRod was talking about. The further each line/ wider V angle between centerlines, the less overlap there will be and less time within the cycle spent with both the intake and exhaust valves open.

Total camshaft advance degree adjusts when the valves are opening and closing against the piston cycle. The valve cycle most importantly effected by advancing the cam degree is the intake valve shut cycle. Allowing the intake valve to shut sooner in the piston cycle, before the piston goes from BDC on it's way up, allows the piston to compress the gas during more of it's up stroke.

Once you've broken down the anatomy of a camshaft, you can begin to understand how the geometry effects how the engine produces power and when it will, in RPM range.

There are a lot of other factors, like how an engine scavenges unburnt fuel from the exhaust (aided by the use of headers, especially equal length, long runners) and how overlap has an adverse effect on it. As you can imagine, when the piston chamber has exposed it's pressure to both the intake and exhaust momentarily, it adversely effects flow, inherently effecting vacuum.

V8 engines have a sister cylinder, meaning there is always a second cylinder drawing the exact opposite stroke in the same position on the other bank. This is why the runners on dual plane intakes are laid out the way they are and why scavenging works. It is also why exhaust balancing is important.

IMO, there are a lot of factors that are just as important as camshaft choice, when buying parts that are commonly overlooked, like piston, head and gasket choice and RPM range for engine balancing.