I have never seen this question before.

when trying to descide on a cam, can you fiqure out what you need by breaking down the cam numbers?


For example , Lift of a cam. If you go with a 509 as opposed to a 494, what would it do to the performance of an engine?

lobe seperation , how it effects Idle and compression.

So say you are build a Street racer. You would think it out and say, I want this thing to Idle so I should go with this lobe seperation. Now I
want , this much compression (so how much lift do I need to fill the cylinders) for best performance.

These questions may seegoofed up and I'm probably not explaining my self right, but the short of it can you break down all the specks to pick the cam.

anotherwards if one cam is:

509 lift , 294 duration and 108 lobe seperation

and the other is

494 lift, 284 duration and 112 lobe seperation

how are the different and how does it effect the running of the engine?

this questions to vauge to be answered in such a short form.the best way you can do this yourself;and analize the results.buy an engine dyno program.then access cam specs from your favorite manufacturer.punch in the numbers you like and veiw the results.its easier than it sounds.and you will learn alot about the relationships you are asking about.also,you can look at online magazines,like engine masters.they have a ton of stuff about cam spec relationships.

Actually you can figure it out from the numbers, it
may not be perfect like a engine builder than builds
hundreds of engines BUT certain things hold true, a
wide lobe will idle smoother than a narrow one(as in
112 vs 108). A short duration will not rev as high as
a larger duration, and lift is based on the heads
abilities (300cfm @ 600). So if you look at the head
flow and your other parts you can figure out the cam.
So for instance you have a good bottom end that can
rev you will want a good duration, the heads flow
good at 600(now you need to figure lash, deflection
and angle of pushrods, if any for losses) and in
this case we will say its a SB so at about .050 over
the head flow. You wanted a good idle thats a wider
lobe, we will say 112, but with the 112 you have
low compression low in the revs so you can add compression.
This is just a quick and simple

If you break down the cam numbers they tell you at which crank position the valves open and close.
For example the 440 HP cam spec is 268/284 advertised duration (I believe rated at 0.006" lobe lift.) Lift is rated at 0.450"/0.458" at the valve assuming a 1.5:1 rocker ratio. The actual cam lobe lift at the tappet is figured by dividing the advertised lift by the rocker ratio.
Anyhow, the cams advertised duration along with the lobe seperation angle determines the amount of overlap the cam has from the point of the intake opening to when the exhaust closes.
In this example the cam had a 115 LSA resulting in 46 degrees of overlap (again using the 0.006" lobe lift numbers.)
The Installed centerline indicates the crank position when the intake lobe is at maximum lift (or the center of the lobe.) In this example the cam is installed with a 113 degree intake centerline to get the valve events described in the Factory Service Manual of:
Intake Opens at 21 degrees Before Top Dead Center.
Intake Closes at 67 Degrees After Bottom Dead Center.
Exhaust Opens at 79 Degrees Before Bottom Dead Center.
Exhaust Closes at 25 Degrees After Top Dead Center.
The overlap is just adding the Intake open at 21 plus the exhaust close at 25 = 46 degrees.
If you change the cams installed centerline to 110 degrees, the timming events are 24/64/82/22.
This "Advancing" of the cam males the intake open sooner before TDC, but close sooner after BDC trapping more compression pressure. On a stock 440 HP this should increase cranking compression pressure about 5 psi. Because the overlap is "ground" into the cam it remains the same reguardless of installed position because it is directly related the the cams lobe seperation and duration.

this article tries to explain pretty much what you are asking, starting from basics:

http://tinyurl.com/aoknat

but take it with a large grain of salt

another view of camshafts from Jim McFarland:

http://www.hotrod.com/techarticles/113_9811_camshaft_tech_valve_timing_piston_movement/index.html

and David Vizard's controversial view:

http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/index.html