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Date:         Mon, 3 Aug 1998 16:26:22 -0700
Reply-To:     Dave Bayer <bayer@SYBASE.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Dave Bayer <bayer@SYBASE.COM>
Subject:      Re: what are ratio rockers?
Comments: To: inua@quicklink.net
Comments: cc: vanagon@vanagon.com

>| Correct me if I'm wrong, but as I recall, rocker ratio combined with the >| design of the cam grind determine when the valves open, how long they remain >| open, and when they close. All together affecting the size of the fuel/air >| charge, thus affecting the force of the power stroke....ie, more torque to >| the crank.

The rocker ratio is a property of a given set of rocker arms. In any event, the timing of when the valves open and closed are all determined by the cam. The cam lobes in combination with the rockers determine the valve lift. The rockers can only effect how far the valves are open - and that is really only in respect to the lift on the camshaft lobe. Indeed, by opening the valves further, you can get a larger fuel/air charge IF the flow characterisics of the head, intake and exhuast systems allow it. But a larger air charge does not necessarily mean more torque or hp (especially over the full rpm range). This is where I get a little iffy on the subject, and why one needs to really understand a bunch of the fluid physics involved. If I remember correctly, the stock cam does have some valve overlap. And while at high rpms, the momentuem of the air/fuel charge will always slam said charge into the bottom of the cylinder, this effect does not really seem to happen as much at lower rpms (because the fuel/air charge does not have as much momentuem). And because I do not understand what is going on at low rpms very well, I don't know if having the valves open further during this overlap period will sacifrice low end torque (which I cannot do on my syncro with oversized tires).

dave


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