What is the actual measurement of a small base circle cam and is it necessary to use one when building a 383? How do you measure the cam to know what it is?

Small base circle cams have lobes that are smaller than a standard camshaft. How big they are depends on the lift profile. I'm sure you can find more info on a cam manufacturer's web site.

You don't have to have a SBCC to build a 383, but it helps. Often times the rod cap bolts will clash with one of the lobes on cylinder 5 I believe. I've been witness to a 393 build that used a standard base circle camshaft, but ended up with H-beam rods to clear the cam.

Your need for a reduced base circle cam depends upon measured clearance (you need a minimum of 0.050"). I use a wire gauge as I have huge paws and measure from the bottom with only one rod at a time (check every rod: as noted some cylinders will clear and others will clash).

An H-beam rod generally has more room on the big end where it will hit with some I-beam rods. The H-beam also clears the pan rail with less grinding because of it's recessed cap screw on the other side of the big end. With a 3.75" stroke you generally do not need a reduced base circle cam with H-beam rods as it will usually clear (It will depend upon the brand of rod and the grind on the cam).

If you can avoid a reduced base circle go with it, as it will yield a stronger cam core (more cross sectional area) to resist torsional stresses such as those 700 pound springs and the drag of a high volume high pressure oil pump. It also negates the need for modified oil slot lifters and longer push rods (the longer the push rods are the more prone to bending they become).

Larger Dave