Part 1: How to choose the correct camshaft for your engine

Awesome. You’ve just completed your restomod, and the only thing left to do is rotate the bendix gear on your starter motor (ya know, by turning the key in the ignition?). So, you turn it on, and it sounds great. Your main goal in life at this point, is to break the motor in (we’ll get more in depth about that one some other time).

The only issue is that while this beast of a motor sounds totally awesome (because you chose the biggest camshaft you could stuff into it) it stalls off the line. It bogs down, and barely even moves.

What the heck is going on here? This thing is supposed to sound awesome and be super-fast. Or at least, kinda fast…

Photo Credit: Edelbrock

Well, remember when you said you stuffed the biggest cam you could find into it? In the world of the camshaft, biggest isn’t always best. We’re going to tackle this issue, but before we do, let’s flesh out what role the camshaft plays in the engine:

The camshaft performs a couple of basic functions. One of which, is to help the intake and exhaust valves open and close. It is also vital to keeping the engine timed; after all, it connects to your timing chain, and ultimately, your crankshaft.

So, what’s the deal?

Well, if your camshaft keeps your valves open for too long, or lifts them too high, your engine won’t run right. If you chose the biggest cam you could find, chances are good your valves have no idea what it’s like to be closed.

Let’s get some terminology out of the way:

• Lift is how far open the camshaft pushes your valves. Each engine has very specific tolerances that it allows each valve to travel, which are measured in inches. So, your engine may accept a camshaft with .450 inches of lift. If they go too far beyond that, they could bottom out. This = bad.
• Duration is the amount of time the camshaft keeps the valves open for. This is measured in degrees. And, a 260 degree cam will hold the valves open for longer than a 240 degree one will. Obviously, opening the valves for a longer duration increases the horsepower of the engine because the amount of air and exhaust gas that is moving is greater. But, this sacrifices low end torque (ya know, that stuff that is required to get your car moving?).
• Lobe separation is the distance between the apex of each lobe. This is also measured in degrees, and used to be called overlap which is the amount of time both valves in the cylinder are open at the same time.
• Duel pattern camshafts have different lift and duration for each valve. This is great if the heads flow poorly on either side; because the camshaft helps the poor flowing side stay open longer, or have a higher lift.

Photo Credit: Comp Cams

Choosing the correct camshaft for you engine is one of the most important things you can do, and is a great starting point for a budget engine build if you have to do things slowly, and cheaply, over time. However, it should go without saying, that if you upgrade the camshaft, you should also upgrade your lifters. The two components develop a wear pattern that cannot be changed by just swapping out either part. Both should be changed.

Before you go out and buy a camshaft, you have to make an important decision. What kind of car do you want to have?

This is a good point to shift gears and tell you about a dude I know. This guy has a gorgeous ’67 Chevelle. He’ll remain anonymous for the sake of embarrassment. He decided that he’d take a completely stock engine and throw a whole bunch of random parts at it without giving it any thought. Needless to say, the car ran like junk afterwards.

So now, he’s trying to figure out why the engine bogs down whenever he mashes the go-fast pedal. The answer is fairly simple, and goes in depth about camshaft choice, along with other important parts of the car.

In the next post, I’m going to cover how to choose a camshaft that works with your application in more detail. Until next time, gearheads.