Modified Mustangs & Fords
Engine Building Part 3 - Power Principles, Heads, Cam, and Intake
Choosing the right Induction components
We mentioned the duration at 0.200-inch and when you look at this duration in accord with the others, it will allow you to "map" out the valve action. Jerking the valves open, holding them open for a long period of time, then quickly closing them can equate to increased horsepower, but you need to be aware of the dangers too.
Now that we can look at the camshaft durations and gather more information about where the peaks will be and how radical the valve action will be, we can also look at the cam's LSA. The LSA is the lobe separation angle. This is basically the distance between the intake lobe centerline and the exhaust lobe centerline. You'll often hear this referred to as the cam's "lobe center." Most street cams are usually in the 110- to 114-degree LSA range and race cams can often dip down into the 106- to 108-degree range.
Increasing or widening the LSA can provide more engine vacuum, better idle quality, and a broader powerband. You'll often see a lot of EFI cams with higher LSA's because it tends to "smooth" out the idle. A cam that hits hard will play with an EFI engine's knock sensor and that's usually not a desired result. Nitrous and forced induction cams will often have wider lobe centers as well. A tighter LSA will often give a more "radical" idle because it has more overlap, which is the amount of degrees that both intake and exhaust valves are open at the same time. It will also affect the engine's manners so that engine vacuum is lessened, idle qualities are a little less clean, and the powerband is often in a more narrowed range, instead of producing a broad curve.
One thing that needs to be mentioned is that engine displacement can, for lack of a better term, "dumb" down a camshaft's specs. For instance, a 302 with a 248-degree (at 0.050-inch) duration camshaft will be a very "high strung" engine with very peaky curves and very poor street manners. However, this cam would be right at home for a street application in say an engine that displaces 529 cubic inches. The more cylinder volume that an engine has, the more duration it needs to effectively fill those cylinders. Camshaft selection is often one of this author's most favorite parts of an engine build. Whoever said that the cam was the engine's brain, we would wholeheartedly agree with that. The cam dictates the powerband, it dictates the manners, and it dictates "the sound." All extremely important aspects of a well-thought out engine build.