How to Select a Camshaft

Camshaft Selection

Before selecting a camshaft, seek advice from a reputable manufacturer. But before making contact, do your homework and have the answers ready for the questions that will surely follow.

 

At their worst, street performance engines are an amalgam of components that don’t complement one another. Mismatching is widespread, and it is for this reason that suppliers of camshafts, and similarly carburetors, explore a long list of questions with their tech line callers.

 

Consider, for example, a 350ci street engine with 9:1 compression ratio, revving to 6,000rpm and fitted with a single-plane intake manifold. The single plane is likely the wrong choice for this combination, impairing air velocity and introducing sluggishness at low revs. Better suited is its dual-plane counterpart that will incite engine speed and increase torque. To correct such inadequacies, a knowledgeable camshaft adviser would select a shorter duration cam to regain air velocity and torque, knowing that a larger camshaft—one with greater duration—would bring disappointment.

 

Other factors that determine the best camshaft for the job

Further questions relate to the vehicle, its weight and purpose. Will it be used on the street or dragstrip or a combination of both? Engine questions will also arise, including cylinder heads, induction and exhaust. The cam adviser will determine the capacity of the cylinder heads, identifying their flow and decide the extent of lobe lift. Knowledge of compression ratio helps shape a more comprehensive picture in the adviser’s mind: an engine running a 9:1 or 10:1 compression ratio indicates a street car, but at 14:1, it’s a race engine.

 

Among the talking points will be carburetors, mechanical fuel injection and electronic fuel injection, and how they influence lobe separation angles. Often, electronic fuel injection systems do not function well with narrow lobe separations, similar to turbocharged, supercharged and nitrous engines. In contrast, mechanical fuel injection systems thrive with a narrow lobe separation angle, and carburetors, which require an amount of vacuum, are placed somewhere in between.

 

Narrow lobe separation angle (for example, 104 degrees), imparts the following characteristics:

 

  • Lower rpm torque range
  • Increase in maximum torque
  • Higher cylinder pressure
  • Lower idle vacuum
  • Rough idle quality
  • Increase in valve overlap

 

Wide lobe separation angle (for example, 115 degrees) will create the opposite characteristics.

 

With regard to drive train, automatic transmissions usually run a slightly narrower lobe separation angle than their manual counterparts. Also, the diameter of the rear tires has a profound effect on the rear gear ratio.

 

Finally, attention will also briefly focus on emission standards, if applicable. Long duration camshafts and stringent exhaust emission rules don’t combine.

 

Types of camshaft and lifters

Any camshaft selection list will include lifters, of which there are four types: hydraulic flat tappet, hydraulic roller tappet, solid flat tappet, and solid roller tappet.

Solid roller arrangements are not as durable in performance street cars as hydraulic roller systems. They tend to wear the bearing mechanism—probably because they rely on oil splash to lubricate the lifter wheel, which at low engine speeds may not always be sufficient.

Hydraulic systems are in constant contact with the camshaft. They have no lash and are thus maintenance-free. While hydraulic roller systems pioneer self-adjustment and are ideal for most performance street cars, they are rev-limited to around 6,500rpm. Hence, it is the solid roller cam and attendant lifters that we rely upon to deliver greater racing revs.

 

For a fuller understanding, here is a typical list when selecting a camshaft