Quote:
Originally Posted by RallyBob
The longer the valves stay on the seats, the longer time you have to build cylinder pressures. A super-long seat-to-seat duration cam is essentially always bleeding off pressure. Bad enough (at low rpms) in an N/A application, but applying boost while simultaneously leaking combustion pressures seems counterproductive...
So while we do want enough duration (and therefore overlap) to aid in scavenging and help the engine to make power in the upper realm, too much overlap can also be bad, particularly with forced induction.
Yes, there is a fine line between fast opening/fast closing and increased engine wear. The cam specs you've quoted would likely be very gentle on the valves and seats. Less spring tension could be run in fact, as valve bounce would likely be non existant
As a rule, most hydraulic profiles are far more gentle than mechanical profiles (except for the intial 'takeup' designed to eliminate the valve lash in a gentle fashion), as the hydraulic buckets can't cope with modern (race oriented) fast acting lobe profiles. They will simply collapse.
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Bob, just so you know, that long duration cam profile is the one for my mates solid Supertech bucket setup, not hydraulics. My setup is the one staying with the hydraulics because it's cheaper, easier and it means I can spend budget elsewhere on the car
whilst sacrificing a little power etc.
Also thanks, good to know about the differences.