Responsiveness of cams 264/264 vs. 264/272 vs. 272/272 [Archive]

Full Function

09-14-2007, 02:04 PM

Here's a write up I had before on the site, but we took it down since we are re-doing some of it.

Intro-
Camshafts are arguably the most important part of the engine. They determine how the car performs, idle, and character of the car as a whole. Understanding the function, design, and limitations of the camshaft will allow you the consumer to maximize overall performance.

Function-
There are a total of four steps of the combustion: intake, compression, power, and exhaust. The crankshaft position, stroke, and rod length generally determine the position of the piston in the cylinder; the cam shaft is what determines the position of the intake and exhaust valves during the stroking process. The camshafts control the valve timing of the engine. This is what makes or breaks the total performance of your car. When the valves open, its how high (lift) and how long they are open for (duration) that determines the performance characters of the engine.

Power Band-
So where does the engine make power? Where does the engine begin to drop power? When the power does come on, is it flat and consistent or is it jumpy and aggressive? These questions can all be answered with the description and understanding of the engine’s power band. A narrow power band would only range from 6000 to 8000 RPM. A wider one would range from 3000 to 7000 RPM. More so than any other internal components of the engine, the camshaft and its complimentary valve train components will establish the power band.

Ideal Cam-
So what’s the perfect cam? The cam with huge low-end torque, a redline set at 10,000 RPM, glass smooth idle, and a power band from idle to redline does not exist. Never has, never will. But an aftermarket performance cam that optimizes the rest of your performance engine does exist. Dollar for dollar, there is a good chance that someone somewhere does make a camshaft that’s the best investment you can make.

Camshaft Shaping-
From a performance standpoint, the faster a valve opens and reaches full lift, the better. Horsepower relates directly to how much air and fuel can actually be pushed into each cylinder, and this can not happen if the valves are not open. Cams that quickly open the valves quickly are said to have an aggressive lobe profile. Unfortunately, the laws of physics govern the maximum amount of possible valve acceleration. If the camshaft tries to open the valve too fast, excessive wear or valve train problems can occur. When returning a valve to its seat, a camshaft once again cannot do this too fast or the valve hits the valve seat. Most of today’s camshafts are designed to optimize valve acceleration rates by designing camshafts with asymmetrical lobes. This is done to lift the valve faster than it lowers. This is done to make the best of your engine’s performance and prolong the life of your valvetrain.

Lift and Duration-
The most basic description of the camshaft’s job is to open and close the engine’s valves. Regardless of the number of cams in a motor, they all do the same job(s). The most well-known camshaft specification is lift and duration. Most of the current manufacturers of performance camshafts list the lift of the valve and not the lift of the camshaft. This may be different for applications other than ones with rocker assemblies.

Lift is nothing more than a measurement of the maximum distance when the valve is opened. Assuming all the other measurements are the same, choosing a camshaft with more lift will increase the flow of air and fuel into an engine and the flow of exhaust out of an engine. Most of the time, cams that have increased lifts over stock specifications and near stock duration will offer increased performance without making large sacrifices in drivability. Everything has a limit and cylinder heads reach a point where airflow no longer increases with an increase in valve lift. Before you jump to ordering a camshaft with a huge lift and duration, remember when valve lift is dramatically increased, the possibility of valve-to-piston contact, and coil bind at the valve spring and valvetrain interference is increased. To avoid bent valves, broken retainers, and empty wallets, make sure you use the necessary complimentary vavletrain components and check your valve to piston clearance to the specifications suggested by the manufacturer.

How long a valve is open is the next influential part of your performance engine. The duration specification of a camshaft is measured in crankshaft degrees of which there are 720 in one complete four-stroke cycle. However, the problem with camshaft duration figures is that different manufacturers measure this duration at different valve lifts. The result of that if we have two different brands measuring the same camshaft would all be different. Luck for us there is industry standards of either 1mm lift or a lift of .050”. When you compare durations between two camshafts, only compare the figures if the measurements have been taken at the same minimum lift.

Duration and Power-
The more lift you have the more repetitive power and torque across the power band in most cases. Generally speaking, increased duration will shift the torque and horsepower peak to a higher RPM. All other specifications being the same, increasing duration yields more top-end and mid-range power while sacrificing low-end torque. By shifting th powerband higher, a longer duration camshaft accompanied with the proper valve train components, will raise the engine’s overall redline. For every 10 degrees you increase the duration, the torque and peak redline will shift 500 RPM.

The Ending Words-
A camshaft may look simple, but completes no easy task in any means. The understanding of function, design, and limitations of aftermarket cams will allow you to make educated decisions about getting the right cam(s) for your car. While its great to have an understanding of cams, leave the designing and measuring up to the professionals. Always remember that the camshaft(s) are just one element of the performance combination. The entire parts combination needs to work together to produce the maximum in power and reliability. Camshafts will only do their job effectively when complimented with the correct valvetrain components.

I hope this helps with your choice.

Jerry