Quote:
Originally Posted by serialk11r
Wait fully retarded intake? What about scavenging?
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Retarded in regards to cam phase adjustment. Doesn't mean no overlop, though I bet it does from the factory (emissions).
Quote:
Originally Posted by Dimman
Ramp rates is the term I think.
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Ramp rates, yup.
Quote:
Originally Posted by serialk11r
Do typical high lift valves have greater ramp rates? (forgive me if that's incorrect usage, I mean peak valve acceleration) If they don't there's no need to have a significantly higher peak...
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I'll try to keep things simple since cams are a component that has their own specialists.
Ramp rate is slimply the amount of lift over degrees and you'll see its a curved slope. From this and engine speed, we can derive velocity and acceleration of the valvetrain components. We can then work out the forces and so on to properly design components.
Now if you were to take given lobe and simply increase duration and lift equally (10% for instance), you'd keep the same curve however velocity and acceleration are going to be higher for the same given engine speed. Further distance to travel in the same 720 degrees.
Now you'll notice on race cams and good performance cams that the lobe is assymetrical. This is because you want to open the intake as fast as possibly and stay there as long as you can. However if you approach the nose too quickly, you'll float the valve and you'll find a hard stop at a piston (bad joojoo) or at coil bind (good way to break a spring and drop a valve = toasted engine)
Now on the exhaust side, you'll see it is a much steeper ramp rate while not allowing the valve to drop so fast that it leaves contact of the cam. If it does, you'll get bounce off of the seat. This is another good way to break things. It'll tear a valve and the head will fall into the engine, or you'll beat the seat back into the head, decrease your lash, which will probably end up leading to a wiped lobe or another failed component in the valvetrain (depends on style of valvetrain).