Choosing a camshaft is probably the most important part of designing an engine
combination, yet it can be the most confusing and frustrating part of your
engine building experience. One of the problems is the confusing and
contradictory way that cams are advertised and the way the specifications are
There are some basic principles that are universal, apply to
all brands of camshafts and must be understood.
- Camshaft size: Bigger or smaller is based on duration, not
lift, more specifically duration @ 0.050" tappet lift. Advertised
duration figures are not reliable numbers when trying to compare one brand
to another for these reasons: first, advertised duration numbers include
clearance ramps, which have no positive effect on performance. Second,
advertised duration figures are not always checked at the same point with
every brand, so the same cam can have several advertised duration figures
depending on who or how it is checked. Third, using the duration @
0.050" is a reliable way to compare cam size from one brand to the
next, a good apples to apples comparison.
When selecting any camshaft for your engine/chassis combination, the size
must be determined by the duration at .050" tappet (lifter) rise.
Using a 1.5:1 rocker ratio this equals .075" valve lift. Any duration
less than this has no positive effect on power.
- Understanding the duration at 0.050" may seem confusing
but the important thing that must be remembered is: as the duration at
0.050" gets larger the camshaft gets larger and vise versa.
- The lower (or shorter) the duration at .050", the lower
the RPM use, such as RV¡¯s, towing, stock engines, etc. As the duration
at .050" increases, the power increases, however, the power band also
moves up in the RPM range. This requires additional engine and chassis
modifications to work best. One cam will not do everything well, you may
have to make "tradeoffs". In other words, if you want to drag
race with a cam that pulls at 6800 rpm, don¡¯t expect the engine to lug a
trailer around at 2000 rpm or vice versa.
- Cams have power bands, "sweet spots" or RPM ranges
that they work best in. This power band or "sweet spot" does not
mean that the cam will not work above or below this range. If, for
example, the sweet spot is rated at 2000-5700 RPM, the engine will still
produce power above 5700 RPM (at least ours will), but above 5700 RPM, the
next larger cam will produce more power. By the same token, cams will
produce power below their sweet spot, but the smaller cam will have more
power there .
- The cam size (duration at 0.050") determines where the
"sweet spot" will be. All brands of cams of the same size will
produce sweet spots in approximately the same rpm range.
- The "sweet spot" will be determined for the most part
by the size (duration @ 0.050") of the intake lobe. Other factors
such as the lobe separation angle, center line and exhaust lobes have some
effect, but these are usually for custom cam installations.
- A change of approximately 5¡ã- 6¡ã duration @ 0.050" is
considered one (1) size or step.
- The power in the "sweet spot" is determined for the
most part by the rate-of-lift or how quickly the valve is kicked open. The
quicker the better (ours are the quickest).
- The best engine combination is when the sweet spots of all the
components (camshaft, cylinder heads, intake manifold, carburetor size,
compression ratio, headers and exhaust size) are in the same RPM range.
For example, an RV torque cam with a large, single plane intake is a very
- If you collect a very poor combination of "sweet
spots" (also know as parts) and then try to pick a camshaft, you
leave the cam supplier with an impossible job. We don't sell cams to
people with really screwed up combinations unless they are willing to
change some components.
- The first component you should pick when you build your engine
is the camshaft. Add the other parts to compliment it, not fight it. Check
our list of questions on choosing a camshaft before you call.
- Our charts lists general guide lines for engine/chassis
combinations. There are exceptions, but "tradeoffs" are
involved. The actual power ranges will vary somewhat with the engine size,
compression ratio (cylinder pressure) and the intake/heads ability to flow
air. If you need more for camshaft information, we will want to know these facts:
- Use of vehicle (What do you expect it to do)
- Altitude of track
- Weight of vehicle (with driver) if a driver is used
- Engine size (cubic inch displacement)
- Cranking cylinder pressure - checked with a compression
- Static or Mechanical compression ratio
- Intake manifold
- Carburetor size
- Cylinder heads
- Cylinder head air flow numbers
- Exhaust type and size
- Stall speed of torque converter
- Final gear ratio
- Tire height and width
- Fuel type and octane
- Will nitrous oxide be used?
- Desired ET or MPH
- Present camshaft
- Rocker arm type and ratio
- Note: Please try to use numbers such as: 1600 RPM stall, not
"stock stall" because Chrysler provided many varieties of stock
- Remember, the more information you provide, the more accurate
the recommendation. We can move the lobe separation angles and mix/match
lobes for very special applications. If you follow these instructions, in
most cases, you will choose the correct camshaft.