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Old 10-24-2013, 06:46 PM
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(Dumb Question) Cam Lift

This cam I'm looking at has a lift of .581. Is that gross, or net lift (after multiplied by rocker ratio)? Don't kill me, I know it's a dumb question lol.



Thanks!

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Old 10-24-2013, 06:51 PM
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That's after multiplying it by the rocker ratio. For a SBC, usually 1.50:1 so your lift at the cam would be 0.387".

Other engines use different ratios in their calculation, but the cam maker should tell what it is.
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Old 10-24-2013, 06:52 PM
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Quote:
Originally Posted by 71K20chevy View Post
This cam I'm looking at has a lift of .581. Is that gross, or net lift (after multiplied by rocker ratio)? Don't kill me, I know it's a dumb question lol.



Thanks!
That would be lift at the valve measured through the effects of the rocker ratio (that would be gross lift), if that ratio is unstated it would most likely be 1.5 times the lobe lift for a Gen I SBC.

Bogie
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Old 10-24-2013, 07:05 PM
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Quote:
Originally Posted by 71K20chevy View Post
This cam I'm looking at has a lift of .581. Is that gross, or net lift (after multiplied by rocker ratio)? Don't kill me, I know it's a dumb question lol. Thanks!
What is the static compression ratio of the motor?
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Old 10-24-2013, 08:22 PM
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What is the static compression ratio of the motor?
to tell you the truth, this is for an LS swap I'm planning. My truck currently has a SBC, but the cam in question is going into a 6.0 LQ4 (9.5:1) or 6.0 LQ9 (10:1).

Most likely, when I get around to it, mods will really only be cam, headers, and computer tune.
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Old 10-24-2013, 08:48 PM
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Though no one has mentioned it yet and it wont apply to your inquiry, with solid lifter cams the net lift will be lower than the advertise valve lift because solid cams have a tappet clearance that is set manually.example maybe .020 between rocker and valve stem when the valve is closed.You will lose .020 times the rocker arm ratio for the net loss of lift over advertised lift.

Enjoy the LS engine,,,
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Old 10-25-2013, 06:03 AM
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The reduction in gross valve lift with solids wouldn't be the lash figure times rocker ratio, the lash is measured on the valve side of the rocker, where it's already past the point of the multiplication(the rocker fulcrom).
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Old 10-25-2013, 07:01 AM
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Ed,you will have to break that down so I can understand?As I see it,the lash can be measured anywhere in the system(valve stem is the easiest) and the ratio is multiplied and measure at the end(valve seat to valve when moved).
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Old 10-25-2013, 07:52 AM
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Originally Posted by vinniekq2 View Post
Ed,you will have to break that down so I can understand?As I see it,the lash can be measured anywhere in the system(valve stem is the easiest) and the ratio is multiplied and measure at the end(valve seat to valve when moved).
Vinnie,as I understand it, since the lash is normally measured at the valve tip/rocker arm junction you just subtract the lash measurement from the gross lift. Example, a cam with .320 lift x 1.5 rocker ratio = .480 gross lift, subtract .020 lash = .460 lift at the valve.
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Old 10-25-2013, 10:54 AM
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If the same cam were used but the lash is measured between the pushrod and the rocker, then the .020 subtracted from the .320 cam lift means it will only raise the pushrod side of the rocker .300", .300 x 1.5 = .450 lift at the valve.
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