Another reason is you will most likely develop a oil leak, probably around the front or rear pan seal, maybe a rear main seal leak with out the vented cap. Excessive pressure will build. Oddly enough, Chevrolet did not put a vented cap with the road draft tube on the solid lifter 270 hp and up engines in the 283 in 1959/1960. Many developed leaks after the fact.
Thanks Steve, I'm glad I asked the question, all of these explanations make sense. Good thing you guys are around to help me stay out of trouble.
Thanks Everyone.
