Cam questions Options

[ThinAir]

I'm assembling the pieces that I'll need to rebuild my 1973 2.0L engine that will retain the stock FI. I'm wondering about cam choices and why I would want to choose a particular one. The only change I've made from stock at this point is that I've got Mahle Euro pistons & cylinders, but they are stock size so there is no increase in displacement.

I hear a lot about the Web Cam 73 and here's the info I've been able to find on how it compares to stock:

Type/Lift/Duration/Duration @ .050
Stock/.392/?/210
73/.426/262/224

Am I correct that Duration is how many degrees both intake and exhaust are open? Or is that called Overlap? If it is called Overlap, does anyone know the specs on the two cams?

What is the difference between Duration and Duration @ .050?

Lift is pretty obvious - the 73 is going to open farther. I assume this means it can deliver more fuel mixture in the same amount of open time compared to the stock lift.

My car is a daily driver that will probably never see anything more exciting than a PCA autocross. So how do I choose a cam and why do I want one or the other?

[lapuwali]

And overlap is the period in which both intake and exhaust valves are open. Race cams tend to have more overlap (more cylinder scavenging by the incoming intake charge), street cams tend to have less. It's overlap that usually causes difficulty with OEM EFI systems, as this increases the amount of "pulsing" in the intake manifold, which confuses MPI sensors in D-Jet, and air flappers in K and L-Jet. Overlap depends not only on duration, but also the lobe centers (where "peak" of the cam occurs relative to the crank). On a single cam engine, the lobe centers are fixed by the cam. On a twin-cam engine, they can be adjusted independently.

Duration at 0.050, btw, means the number of crank degrees that the valve is 0.050 off its seat, rather than the whole time the valve is off the seat. I've also seen numbers quoted as 0.040 off the seat, which will make a cam appear to have longer duration than the same cam quoted at 0.050. These numbers are usually quoted because when you measure the cam on the engine itself, it moves so little and so slowly at the beginning of the movement that it's often hard to tell exactly when the valve starts moving. It's easy to make an error of 10 crank degrees or more if you try to use 0 instead of 0.050. By the time the valve is open 0.050, it's moving fast enough that you can pin it down to one crank degree pretty easily.