Determining the correct valve geometry??

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Determining the correct valve geometry??

Post  HorsinAround on March 8th 2012, 4:30 pm

I am trying to learn how to find the correct valve geometry and came across this from Comp cams. http://www.compcams.com/Products/CC-'Pushrods'-0.aspx As I read looked at their sketch and read the commentary I am puzzled because it seems backwards to me. If I am reading it right, it says the proper geometry is when the roller tip starts on the intake side and ends up on the exhaust side of the stem at full travel. Now, my mind is thinking that if the stud is the pivot point and the rocker is traveling in an arc, it seems to me that the roller tip would get closer to the intake side as the cam pushes the roller down wouldn't it?
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Re: Determining the correct valve geometry??

Post  TRUKPULR on March 8th 2012, 9:09 pm

Yap your right
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Re: Determining the correct valve geometry??

Post  Onequickfiveoh on March 8th 2012, 10:17 pm

Not necessarily. Think about it. If your pushrod is to long then yes it will begin on the exhaust side and move inwards. Shorter pushrod will be the opposite. Base circle portion of the cam the rocker should be angled up therefore tip being on intake side then thru the lift it should go to the exhaust side on peak lift. Pretty sure comp knows valvetrain geometry. How many years have they been in business?
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Re: Determining the correct valve geometry??

Post  fordpullin on March 8th 2012, 10:36 pm

Onequickfiveoh wrote:Not necessarily. Think about it. If your pushrod is to long then yes it will begin on the exhaust side and move inwards. Shorter pushrod will be the opposite. Base circle portion of the cam the rocker should be angled up therefore tip being on intake side then thru the lift it should go to the exhaust side on peak lift. Pretty sure comp knows valvetrain geometry. How many years have they been in business?

Yea like he said cheers
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Re: Determining the correct valve geometry??

Post  BOSS 429 on March 9th 2012, 12:05 am

HorsinAround wrote:I am trying to learn how to find the correct valve geometry and came across this from Comp cams. http://www.compcams.com/Products/CC-'Pushrods'-0.aspx As I read looked at their sketch and read the commentary I am puzzled because it seems backwards to me. If I am reading it right, it says the proper geometry is when the roller tip starts on the intake side and ends up on the exhaust side of the stem at full travel. Now, my mind is thinking that if the stud is the pivot point and the rocker is traveling in an arc, it seems to me that the roller tip would get closer to the intake side as the cam pushes the roller down wouldn't it?


look at everything, rocker ratio also
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Re: Determining the correct valve geometry??

Post  rmcomprandy on March 9th 2012, 12:41 am

HorsinAround wrote:I am trying to learn how to find the correct valve geometry and came across this from Comp cams. http://www.compcams.com/Products/CC-'Pushrods'-0.aspx As I read looked at their sketch and read the commentary I am puzzled because it seems backwards to me. If I am reading it right, it says the proper geometry is when the roller tip starts on the intake side and ends up on the exhaust side of the stem at full travel. Now, my mind is thinking that if the stud is the pivot point and the rocker is traveling in an arc, it seems to me that the roller tip would get closer to the intake side as the cam pushes the roller down wouldn't it?

Only if the fulcrum of the rocker arm is too high in relation to the valve stem tip.

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Post  HorsinAround on March 9th 2012, 9:33 am

I was thinking about this again last night, and I think I see my flawed thinking. the centerline/pivot point of the rocker is lower than the top of the valve stem, so that changes the point in the travel radius where the roller contacts the valve stem tip.

Thanks for the input. Always helps
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