If you were building a house how would you decide what heating system to install? If you built the house without glass in windows you would need a very large heater. If you built the house with no openings except a door you may need a different system. If you built the house to live in Alaska you would need a different system altogether than one built for Hawaii! And the choice of camshaft is very similar. We often get calls from people who are about to build a new motor and have not considered any of the other many things that must be included and are trying decide on a camshaft believing that picking the right camshaft was all they needed to be concerned about.
Camshaft selection can be as complicated as you like, but for the ultimate performance, even if that means best gas mileage, requires that you consider the entire envelope that the camshaft will work within. Non-technical issues such as intended application (street, race, milage or??), budget, expected RPM range, etc must be considered along with technical things like compression ratio, Cylinder head and valve sizes, exhaust system, carburetion, etc.
Camshafts although available from a number of manufacturers can all be grouped in some general categories: Stock, hot street, high performance and full race. Each of these categories have their own characteristic but compression ratio is key.
In today’s world of lower octane fuel, the hope to get increased performance by simply raising compression with a ‘hotter’ camshaft has long gone. In 1967 a stock street Cooper “S” had a spec of 9.75:1.
A “stock” camshaft today it typically has less than 260 degrees duration and compression under 9:1
A “hot street” cam has a duration of less than 276 degrees a compression at least 9.75:1
A “High performance” cam will be less than 290 degrees and a compression of at least 10:1
A “Full Race” camshaft will have a duration higher than 290 and a compression at least 12:1
The Mini Mania library of technical articles contains a wealth of both basic and advanced information:
”Considerable information has been recorded about numerous aspects of the four stroke internal combustion engine. Nevertheless, only a small percentage of people really understand how it works and even fewer still know how to modify an engine to suit their needs. I will try to simplify this complex subject by discussing some basic principles that may be overlooked or misunderstood by the average person. First, it is very important to understand the relationship between piston travel directions and valve timing events. The reason this relationship is important is because it is one of the few things that is relatively easy to adjust/change.” ….more
This whole 'scattering' deal has befuddled many. The only real prose produced on the subject, and 'advice' handed out by many so-called 'specialists' tends to be somewhat tainted with large chunks of mysticism - inferring there's some kind of black art involved. The simple fact is the principle is very basic and easy; it's getting a cam with the right profile and figures applied to it that will actually work as a scatter profile that's the hard part. I will illuminate …..More
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