If you want improved horsepower and or better fuel economy then changing the camshaft is one of many options open to you. Generally because of the costs involved in fitting a cam, some car owners opt for cheaper add on goodies to either gain horsepower or get better fuel economy. The selection process of choosing a cam can be daunting and is best left to the experts to help you choose especially if you own a Ford, Chev or Holden V8. The choices are many but for other engines the choices are limited and very simple to choose which cam you would like, unless of course you get a custom grind. The manufacturers will supply all the information you need to make the correct choice of cam to suit what you want to accomplish. However if you want a cam that produces 50% more horsepower but still want the economy, then that is not possible with a fixed duration camshaft. Big cam profiles and fuel economy just aren't used in the same sentence. However there are options for gaining a little more power and still retaining your stock cam economy. You may like to consider fitting a special set of hydraulic lifters to the cam that will give you the best of both worlds, the power increase the cam provides and still retain good economy if you drive it steady. See my article in Product Reviews on Rhoads Lifters.

Many factors are taken into account when choosing the correct cam for the job. Obviously make of vehicle, model and engine size are the first factors to choosing the correct cam to fit your engine. What max RPM do you expect to rev the engine to, be realistic here, if you don't intend to do any further mods to support the cam then asking for a high rev cam without adding bigger carburation, intake manifold or a decent exhaust to support the cam will lead to disappointment, not to mention that the bottom end might not take to kindly to high revs without being beefed up somewhat. The current diff ratio, manual or auto transmission will also dictate what cam choices you have unless you modify the stall of the converter in an automatic.

Cam Data in brief may be now appropriate to discuss. 16-56, 20-60, 25-65, 30-70 are common cam specs in reference to advertised duration. In these cases the inlet and exhaust cam profiles could be identical and mirror images of each other when split down the TDC line depending on the Intake Centre Line (ICL) & the Lobe Seperation Angle (LSA).  These are also known as single pattern cams. Some can be symmetrical, meaning when the opening & closing points of the lobe are the same angle either side of the lobe centreline then this is symmetrical. I will use the 20-60 profile to explain what the numbers mean. The first number is when the inlet valve will open BTDC, (20 deg) and the second number represents when the valve will close ABDC (60 deg). The exhaust will open 60 deg BBDC and close 20 deg ATDC. The valve overlap at TDC will equal 40 deg and the duration of the cam is 260 degrees. The lift at the valve after calculating rocker arm ratios would be about .440" and varied significantly depending on grind profile, however this is not shown in this drawing, I am only taking an educated guess from my experience with a cam of this size. In a 6 cyl or V8 this is considered a very mild cam and will idle just slightly rougher than a stock cam. This cam will produce a nice gain in low down torque and power with little to possibly no loss of economy. The more valve overlap and cam duration you have as in the 30-70 cam, the more the horsepower improves and the more fuel you will consume, especially if you use the available horsepower. Also the quality of engine idle deteriorates with larger overlap angles, smaller LSA's, as well as high lift rates and requires the idle speed to be raised. Typically an early model stock V8 will idle at 650 RPM, but fit a 30-70 cam and the idle will be around 800 RPM and a little rough. You can't mistake the sweet sound a wild cam makes when it is timed and tuned correctly.

The table below shows the effect of advancing and retarding the camshaft. This may be necessary if you just can't find the right cam for your purposes. The cam is generally retarded or advanced by about 4 crankshaft degrees. This will shift the cams advertised power and torque settings by approx 500RPM.  LSA is not adjustable and is set by the cam grinder. Below you can see what effect this has on cam performance. This table is in reference to a single cam not a DOHC. There are thousands of combinations of cams out there to choose from, that's why I say you need to trust the salesman to make the right choice.

I have not yet mentioned a spec that is used to determine the rate of cam lift. This specification "X degrees at 0.050" on a camshaft refers to the duration of valve opening measured at 0.050" of valve lift and is the standard in the performance and racing industries. This spec is quite important as it is a measure of the rate of lift of the cam. In other words, how quick the valve is opened.

Advertised Duration vs. Duration @ 0.050"

Advertised Duration: Typically measured at .004"–.006" valve lift which includes the opening and closing ramps of the lobe.

Duration @ 0.050": Starts after the ramps during more meaningful valve lift. It's a much better reflection of actual airflow timing.

The difference between advertised duration and .050" duration tells you something about how steep or lazy the ramp is.

The larger the gap between advertised  @.050" and the advertised duration the softer/slower the ramp, and likely a milder cam in terms of how hard it hits.

Knowing only the duration @.050" without knowing the advertised duration means nothing and the performance of the cam cannot be judged from this specification alone. As per the table above, remove all the rows and only leave the .050" spec there and what are you left with. An almost meaningless figure on its own except to know that one is possibly more radical than the other.

Flowing on from here, you may appreciate that the rate of lift will also determine which lifter you will use. The milder cam will easily run with flat tappets, (hydraulic or solid) which don't have an aggressive opening or closing ramp. Using an aggressive cam however will require the use of solid roller lifters so that it can follow the cam profile. A normal flat tappet lifter would not clear the leading edge from jamming into the camshaft lobe.

Modern grinds are a fair bit different now to the old days. Big money has been poured into R&D to develop new grinds that will satisfy almost all rev heads. Enough on this, lets move onto cam re-grinds.

Below are two examples on how a regrind on an old cam is done. The pictorial on the left shows that the cam is built up by welding material between the opening and closing points and then grinding it to shape leaving the base circle at almost its original diameter. The next method is more common as long as the worn shaft still had a good nose but very unlikely. It was very easy to just grind the shaft down. Sometimes a combination of repair could be done. Which ever method was used in the camshaft reclaiming, there is one certainty in the final product adjustment. The geometry of the rocker will be comprimised and will require geometry adjustments to be made to maintain correct geometry of the rocker arm from its closed to full open and closed again positions. Now that is another very indepth discussion.