COMPUTER COMPATIBLE CAM SELECTION 

What exactly does the computer "look" at regarding duration and lift? How far can I go without causing computer and emission problems?

The computer in a feedback carburetor application dictates ignition timing, based on engine vacuum as read by the MAP sensor, plus engine rpm. Working throught the mixture-control solenoid, the computer also helps adjust idle and part-throttle fuel metering. However, when the secondaries are at WOT, the feedback carb operates as a conventional carb in open-loop manner. This means you can tune the secondary side by changing metering rods and hangers. On the primary side, you can go up to .002-inch richer on jet sizes, but do not change the primary metering rods and leave the duty cycle solenoid alone.

Keeping idle vacuum up is the key to avoid computer problems. Tuners increase idle vacuum with a hotter cam by advancing initial timing 5 degrees. However, the smog computer may examine timing so use an aftermarket Stage I chip that bumps up the timing internally.

As far as cam selection, increasing the lobe separation angle from the 110 to 112 degrees improves idle stability and vacuum output, at the price of some initial reduction in throttle response and low and mid range torque. However, with the SS rear gears (3.42 or 3.73), you can afford to give a little on the bottom.

Another way to enhance vacuum is using quick-opening and -closing ramps on the cam. This is judged by looking at the .050-inch duration numbers. The close the advertised duration is to the .050-inch duration, the quicker the cam, assuming advertised duration is measured at the same point on each cam.