So the first parameter that we need to identify is where in the engine's rev band you want the peak torque to occur. Generally, an engine's peak horsepower engine speed will be about 1500 to 2000 RPM above the engine's peak torque engine speed. The shape and rev range of the torque curve will by definition define the engine's horsepower since the two are related by the following equation: That is to define the shape of the torque curve.
What sort of fuel will be used - specifically what octane?Īll of the factors of a cam's design do only one thing when it comes to engine performance.What sort of induction system are you planning on using? Carbs? MFI? CIS? EFI or Individual Throttle Bodies?.Where are you going to use it? On the street? Track? Race? Are emissions important?.
If you are running the relatively wide gearbox from a 4 speed 911T on the other hand, you might actually consider targeting a wider rev range. If you are running a close ratio gearbox you'll be able to optimize the engine's rev range for a smaller drop in rev's after every shift. The desired rev range is really a function of the intended gear box and the gap between gears.
What is the desired rev range? For the sake of discussion it would be best to pick a 2000 RPM range where you want the engine to be strongest. Step 1 - Define the Performance Parametersīefore you buy anything it is important to define a set of goals for your engine. By the careful management of these factors it is possible to select a camshaft that will work in concert with the other components in the engine and optimize its performance. How it does this has a fundamental impact on the speed with which each cylinder is filled, the acoustical tuning of the exhaust and intake systems and the functional compression ratio of the engine. My intention is to introduce the key facets so that reader can be confident that they are “in the ball park” and have a meaningful conversation with their engine builder or cam designer.Īt it’s simplest, the function of a camshaft is to open and close an engine’s valves in synchronicity with the pistons cycles. Please keep in mind that camshaft design and the interactions between the camshaft and the engine is a very complex subject which could never be covered in a few paragraphs. In this article I will be outlining a process that can help you to select the right camshaft for your air cooled normally aspirated 911’s engine. As a result the camshaft is often selected as an afterthought which can result in unintentional compromises and an engine that doesn’t perform to its full potential. 
Camshafts are one of the defining elements of an engine’s performance and often one of the least understood.
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