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1. How do I go about selecting a cam based on
my desired engine rpm range?
Many variables determine the rpm range and torque curve –the “powerband” of an engine, including cubic inch displacement, cylinder head characteristics, intake manifold, camshaft specifications and others. Note that larger displacement engines require more duration than smaller ones because they require more air/fuel mixture to fill their larger displacement cylinders.
The most important aspect of camshaft (and other component) selection is to have your specific rpm “goal” in mind before you begin to select engine parts. A camshaft should be close to the last item on your list –chosen to match all of the other performance pieces on your engine. Remember that the best way to select a camshaft is to ask an expert to help you select the right camshaft based not only on the size of your engine, but on your entire combination of parts.
When seeking assistance in selecting a camshaft, it is important that you can provide the weight of your vehicle, transmission type, converter stall speed, rear end ratio, engine displacement, compression ratio, and whether it will be normally aspirated, or if you intend to run a power adder such as nitrous, a turbocharger, or a supercharger. Each of these variables must be considered when choosing a cam, and the more accurate the information – the better your new camshaft will perform.
2. What is the difference between intake
centerline and lobe separation angle?
These two terms are often confused. Lobe separation angle (LSA) is simply that: the number of degrees (denoted by the ‘°’ symbol) separating the peak lift points of the intake and exhaust lobes. Lobe separation is effectively “locked in” when a camshaft is ground and cannot be changed. Note that a tighter lobe separation (smaller LSA number) results in a narrower and peakier torque curve, and a wider lobe separation (larger LSA number) produces a broader torque curve.
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The intake centerline is the position of the centerline (or peak lift point) of the intake lobe in relation to the Top Dead Center position of piston travel. Intake centerline can be adjusted by degreeing your camshaft, and can have the effect of increasing off-idle torque (advancing) or increasing peak RPM (retarding) .
For example, if your camshaft has a 110° LSA, and you install it with 4° advance, your intake centerline is 106° after Top Dead Center.
3. My motor is currently normally aspirated, but I
plan on installing a power adder. Can I use the
same cam for both applications?
Normally aspirated (N/A) engines and boosted engines generally require different camshafts for optimum efficiency. Typically, camshafts intended for use with power adders will feature a wider LSA and more exhaust duration than those intended for use in a non-boosted application.
A few important points:
• Each type of power adder is different and so are
the cams that work best with them. Variables such
as boost pressure or nitrous horsepower shot must
be taken into consideration to ensure consistent
performance.
• Nitrous creates a lot of cylinder heat and requires
more exhaust duration to help evacuate the cylinder.
• Superchargers also increase cylinder heat and tend
to work more efficiently with a wider lobe separation.
• Turbocharger technology has come a long way.
Again, many variables should be considered,
but in general you don’t need a very large cam.
Turbo cams in fact, should have less exhaust
duration than a N/A cam.
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