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Adger Smith · 06-26-2011, 11:52 AM

Lonnie,
You got some very good answers in this thread.
I would never consider moving the cam around, very much, to get PTV clearance. Depending on the lobe profile & rocker ratio you only get between .005 to .008 clearance (change) per degree of cam movement. Some more, some less....
Another issue with retarding the cam is the ex valve will open at a later point in the cycle. A late opening of the ex valve can be a problem when trying to produce power at high rpm. At high RPM it can cause lost power by what is called pumping losses. At High RPM the late opening causes the Ex to loose some of the blow down affect and the piston has to pump the spent ex gasses out. In real bad cases there can be ex gasses trying to go back into the intake runner when the intake valve opens. That really kills power.

06-26-2011, 11:52 AM	#10
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: Intake Center Line Lonnie, You got some very good answers in this thread. I would never consider moving the cam around, very much, to get PTV clearance. Depending on the lobe profile & rocker ratio you only get between .005 to .008 clearance (change) per degree of cam movement. Some more, some less.... Another issue with retarding the cam is the ex valve will open at a later point in the cycle. A late opening of the ex valve can be a problem when trying to produce power at high rpm. At high RPM it can cause lost power by what is called pumping losses. At High RPM the late opening causes the Ex to loose some of the blow down affect and the piston has to pump the spent ex gasses out. In real bad cases there can be ex gasses trying to go back into the intake runner when the intake valve opens. That really kills power. __________________ Adger Smith (Former SS)