You did not indicate what the vacuum readings were, but it is not uncommon to see modern automobiles with a lower cruise reading than what was considered commonplace 15 years ago. Smaller engines tend to run at lower vacuum readings since they operate in a higher power level than a large engine. Also, an engine running with a lower vacuum reading is losing less power than a larger counterpart due to suction throttling losses.
For example, in a 3500 lb auto with a 3.0L engine, it MIGHT be running at highway speeds at 9"hg, where as the same vehicle with a 5.7L engine may be running at 16"hg. Guess which one will get better economy?
Cam lobe profile can certainly cause problems as patprimmer indicates, but to add my small and barely significant thoughts, once a camshaft wears to the point where valve lift is compromised enough to cause a loss in power, the valve followers should be rattling like a bucket of rocks, and it just gets worse, fast. Once the camshaft lobe hardened surface is cut through and the followers suffer the same wear rate, the resulting action more closely resembles a bench grinder than a precision engine.
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
