How to measure camshaft lift - Team Camaro Tech
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post #1 of 7 (permalink) Old Nov 3rd, 00, 05:13 PM
Rich253
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I recently purchased a rebuilt SBC from a local shop. I ordered it with a camshaft with a lift of .454, why is it that when I measure the lift of the hydraulic lifters, they only lift out of their bores about .300? Does this mean I got the wrong cam? Does any SBC have a lift of only .300? Or is there something I'm missing. I notice that if I divide .454 by .300 I get 1.5, which I believe is the ratio of standard chevy rocker arms.
Is the proper way to measure lift, to multiply the distance the lifter rises out of it's bore, by the rocker arm ratio? (.300 X 1.5= .450) This would give me approx .454
Rich
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post #2 of 7 (permalink) Old Nov 3rd, 00, 05:25 PM
 
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I believe that the hydraulic lifter is designed to pump up with oil when the engine is running and therefore would not give accurate measurments when the engine is not running. Use a solid lifter and you should be able to more accurately check cam lobe lift at the lifter.

Joseph
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post #3 of 7 (permalink) Old Nov 3rd, 00, 08:11 PM
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You are correct about multiplying the lifter rise by rocker ratio.

Steve R.
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post #4 of 7 (permalink) Old Nov 4th, 00, 03:40 AM
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You should ask the engine builder for the cam info sheet that comes with the cam. If he doesn't have it at least get the cam part number and manufacturer then you can look up the info. A company like Crane Cams has the info on their web site.
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post #5 of 7 (permalink) Old Nov 4th, 00, 07:43 AM
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There are two different ways to measure lift: At the lifter and at the valve. The total lift figure of .454 is at the valve. The .300 you measured is at the lifter. However it is important if you have non-stock heads or valvetrain to measure both at the lifter and at the valve. The reason for this is that your pushrod length could be off. If your pushrods are too short, then Both the lift and duration will be smaller at the valve, or visa versa if the rods are too long. You must have the cam card in order to have the correct measurements to check for. While you are at it you might as well check your lobe center and make sure the cam is not off a degree.
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post #6 of 7 (permalink) Old Nov 4th, 00, 09:01 AM
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For more info get a look at the back of an Isky Cams catalog.
They have a bunch of info on several ways to degree cams and how to check your pushrod length etc.
If the pushrods are off, the rockers will have a side thrust on the valve stem which will wear out your valve guides and can even break parts.
At .454 lift, you aren't pushing the parts very hard and should have little trouble with that stuff.
But if you have the time it would be good to check it out, especially if you have a decked block, different thickness head gasket or aftermarket head or cam.
David.

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post #7 of 7 (permalink) Old Nov 4th, 00, 05:12 PM
Rich253
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Thanks for the replies. I learned something new! I checked out a couple of cam websites as suggested. The Comp Cams site lists specs. for all their cams. They list not only lift, but also something called gross lobe lift. When I multiply the gross lobe lift by 1.5, it matches the total lift number. I guess gross lobe lift is what I am measuring when I measure the distance that the lifter rises out of it's bore. Now that I have a better understanding , I will measure the lift at the valve, to verify pushrod length, as was also suggested.
Rich
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