1985 4x4 Crate Engine Swap old school 350 or Vortec 350

[rich weyand]

A further note on modern vs older cam designs. When designing a cam, you really want the valve to be completely open when you want it open, and completely shut when you want it shut, but you can't have that: it has to move between the two positions.

Compression will not begin until the cam is completely shut, and the power in the power stroke will end as soon as the cam opens and dumps the pressure in the expanding charge. On the other hand, good flow into or out of the chamber will not begin until the cam is pretty far open.

Cam design is a compromise between these issues, tuned to the purpose of the engine, including the weight of the vehicle and how it will be used.

These compromises got a lot less severe with the high-speed ramps of modern cam designs. Using computers, it was much easier to speed up the ramps on the cam -- have less time between partially open and fully open -- and still maintain reasonable wear and not float the valves. The computer can figure out the cam-to-lifter pressure at every point on the cam lobe, at every rpm, and all that sort of thing. So cam ramps have gotten much faster. The result is that, with a modern cam design, compression can start sooner, raising the dynamic compression ratio and therefore torque, and the push on the power stroke can last longer without cutting into flow rates, increasing both torque and horsepower.

The best way to tell a modern cam design from an old one is to subtract the .050 valve duration from the advertised duration. Old-school cams may be 70 degrees difference. Modern cams will be more in the 40-50 range. The difference that makes on the performance that can be achieved in tuning the other cam parameters should not be underestimated.