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View Poll Results: measuring cam lift
follow the diagram and you will get the proper lift value 4 50.00%
following that diagram will NOT tell you the lift of a cam 1 12.50%
the rest of the valve train has everything to do w/ lift @ the cam 1 12.50%
the rest of the valve train has NOTHING to do w/ lift @ the cam 4 50.00%
camshaft lift doesnt exist on DOHC cars, only pushrods cause lift 0 0%
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Old 10-01-2007, 10:48 PM
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how to properly measure the lift of a cam ? NOW WITH A MULTIPLE CHOICE POLL!!!

ok, this debate keeps going on a different forum, the threads even been locked and im getting private messages and even messages through aol debating weather or not im right

simple problem:

a friend went to purchase some reground cams
he measured base circle
he measured overall lobe height
he did some simple math
simple match says LESS LIFT THEN STOCK

the cam was measured in this fashion:


is there any possible way that you can do a-b=c and have a not be the actual lift on the camshaft?

the only reason i can think of is that the cams TOTAL duration is high enough that it interferes with measuring base circle (which definantly doesnt apply in this case)

a variation of this reason is that the person that did the measurements is incapable of operating a set of dial calipers (causing him to accidentaly include one of the ramps in his attempt at measuring the base circle) but said person in this case has machine shop quality control experience

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Old 10-01-2007, 10:50 PM
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Yes, c-b=a.
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Old 10-01-2007, 10:52 PM
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Quote:
Originally Posted by lowROLLERchevy
the cam was measured in this fashion:


is there any possible way that you can do c-b=a and have a not be the actual lift on the camshaft?

the only reason i can think of is that the cams TOTAL duration is high enough that it interferes with measuring base circle (which definantly doesnt apply in this case)

a variation of this reason is that the person that did the measurements is incapable of operating a set of dial calipers (causing him to accidentaly include one of the ramps in his attempt at measuring the base circle) but said person in this case has machine shop quality control experience

IF the ramps do NOT interfere with the measurements, I see no problem with how you did it.

Personally, I'd use a dial indicator on the lobe and rotate it through one full turn and note the minimum and maximum readings, then subtract. But in your case with a fairly stock cam, yours should be fine!

Mark

BTW.....very important thing here that should not be overlooked.........DON"T BUY A REGROUND CAMSHAFT!!! LOL

Last edited by Jmark; 10-01-2007 at 10:57 PM.
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Old 10-01-2007, 11:11 PM
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Quote:
Originally Posted by Jmark
BTW.....very important thing here that should not be overlooked.........DON"T BUY A REGROUND CAMSHAFT!!! LOL
they were cams for a niche market vehical, noone makes new cams, the only options are regrinds or find someone to make a single set of custom billet cams

on a DOHC v6, that seams to be about $1200. or the other option for this car is $550 for a set of already proven regrinds ... and in this case we were considering buying what was said to be one of those sets of regrinds, slightly used, for $250

almost a grand in savings is hard to say no to (except when the specs show that said used cams dont meet the regrind specs, lol)
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Old 10-01-2007, 11:28 PM
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measure lift of cam lobe

I missed something.
the simple math formula is wrong.
to get lobe height you subtract b from a to get lobe height.
A-B=C
Bear
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Old 10-01-2007, 11:50 PM
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^^^ nope, your not missing anything, i jumbled the letters somehow, lol

fixed in my original post now, but luckily i had the other description right above the image, removing some of the confusion
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Old 10-01-2007, 11:55 PM
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If the total lifter off base circle duration is more than 360deg (crank degrees) Then the cam could appear to have less lift using that method to measure lift.
A racing cam could easily have more than 360deg of total duration including lash ramps. Most stock and moderate performance V8 pushrod cams can be measured using this method to find the basic lobe lift as the total duration is less than 360 deg. But some radical long duration race cams cannot.

The cam lobe also has a slight taper accross its width. So you have to measure A and B on the same spot across the width of the lobe to get accuracy.
The slight taper on the lobe combined with lifter offset makes the lifter spin when the motor is running.
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Old 10-02-2007, 08:30 AM
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What he said
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