March 26, 2012

Camshafts

We could talk all day long about camshaft selection and still just scratch the surface. There's no way we could discuss every possibility for a particular engine, so our aim here is just to hit the major points and try to illustrate what to look for when planning a particular engine build.

When you look at camshaft specs, you'll see terminology such as duration, LSA, and lobe lift. There are many specifications that are used to describe a camshaft's personality, but these are the most common. Just like all of the other engine components that we've described in the past few articles, camshaft selection is extremely important, and a cam must be chosen to fit the application. The cam is often deemed the "brain" of the engine and rightly so. Its job is to open and close the valves at just the right time, so it essentially controls the engine's personality. Choosing the wrong cam can really put a damper on your day, but picking the right one can make you exercise your face muscles in a good way. So let's go over some terminology and see how it applies to your engine plans.

First and foremost, we have different types of camshafts: hydraulic flat tappet, solid flat tappet, hydraulic roller, and solid roller. Your application should greatly dictate the type of camshaft you need to run, but here are a few things to consider:

Hydraulic Flat Tappet Pros: Inexpensive. Low maintenance once broken in.

Hydraulic Flat Tappet Cons: Camshaft break-in can be tricky and there is always a chance of break-in failure. Rpm limits should be kept in the 5,500-6,000 rpm range, as valve float is a prevalent problem with hydraulic camshafts.

Solid Flat Tappet Pros: Inexpensive. Little more maintenance is required as valve lash can change. Can handle high revs.

Solid Flat Tappet Cons: Same issue with break-in as the hydraulic flat tappets.

Hydraulic Roller Pros: More expensive than the flat tappet camshafts. Expect to pay about $125 more for a cam/lifter set that uses factory-style lifters. If you're going to use link bar lifters, then you can add a few hundred bucks more to that figure. A hydraulic roller cam is the least painful of all cams. No cam break-in, no maintenance. Shove it in the motor, adjust the preload, and call it a day.

Hydraulic Roller Cons: Rpm limited. In a Ford engine with larger valves, 6,000-6,500 seems to be the upper rpm limit, depending on the spring/retainer package that you're using. Anderson Ford Motorsport does offer hydraulic roller cam and spring packages that are purported to have rpm ranges of 7,700 or more, but this isn't the norm. Typically hydraulic roller cams don't like to rev, especially with the larger valves (2.05- to 2.300-inch) that we see in SBF-BBF engines.

Solid Roller Pros: Lots of horsepower potential due to aggressive lobe designs. Also, lots of rpm potential with the correct valvespring package.

Solid Roller Cons: Can be pretty expensive, especially when you're looking at some good pressure-fed lifters. Pricing can approach $1,000 for the cam and a quality set of lifters alone, not to mention expensive valvesprings if you're planning on radical lobes and a super high rpm range. Solid rollers require a little more maintenance than the rest of the cams. Valve lash needs to be checked periodically, like the flat tappet cams. Also, valvespring pressures need to be tested in different intervals, due to the fact that a more aggressive lobe design will weaken the spring steel. In addition to those items, solid roller lifters lead a rough life. The bearings in the lifter wheel take an extreme amount of abuse because of valve lash coupled with high spring pressures. It's a good idea to R&R them as well.

Those qualifications should give you a warm fuzzy feeling for which direction you need to head. Again, be honest with yourself, and make the engine fit the application. Yes, you'll be saying that in your sleep before too long. "Honey, you woke me up last night making speed shifting noises and saying something about making the engine fit the application. Oh, and by the way, you slept with a connecting rod under your pillow." Yes, it happens to all of us.