Cam lobe specs?

[turbov6joe]

What I need to know is if anyone has any idea what would be a tollerable range between cam lobe measurements? I was measuring a Comp Cam and between the lowest and highest measurements I had a difference of .021.
I measured a Lunati cam and the same difference was only .006. I wonder if Lunati and Comp have different ideas of what are acceptable ranges at manufacture??? What's very odd was that the Lunati had an advertised lift of .426.....the lowest measured lift I had was .440 and the highest .446; WTF The Comp has an advertised lift of .459, the lowest I measured was .454 and the highest .475; WTFx2 The Comp cam has approximately 500 miles and the Lunati prolly 15k.

 

[Matt Sando]

sometimes they spec.the cam @.050

(for example: .508 duration @.050)

 

[Mike Licht]

How did you measure it? you need to put it in a block or a set of v blocks, put an indicator on the lobe and spin it around. Set the indicator to zero when it is on the heal you can then see lobe lift.
Mike

 

[NCTURBOS]

Also keep in mind that Gross Valve Lift and Lobe Lift are two different measurements. Don't get them confused with each other.


K.

 

[Mike Licht]

Right, to get Valve lift multiply lobe lift X rocker ratio = valve lift
Rocker ratio for stock rocker is 1.55 so if your Comp cam is rated for .459 valve lift it will be about .296 at the lobe
Mike

 

[TurboTR]

Sounds like you are maybe just measuring the diameter of the lobes, and seeing the difference in base circle diameters?

TurboTR

 

[Ormand]

Sounds to me like he was measuring the lift at the valve. That would give approximately the "advertised" lift, but the tolerance stack up, from cam lobe to rocker ratio, would make the measurements vary. But if both sets of measurements were on the same engine, then the cam would have to account for most of the difference, not the rockers. More info, Joe!

 

[turbov6joe]

I used a slide mic and placed the lobe ramp on the sliding part of the mic and rotated the cam until the dial indicated that the numbers had quit raising, all the while keeping my thumb on the slide for a little resistance. I then went slightly past full rise and watched it decrease...then rotated it backwards to it reached the high number again...that's the number I used; did this twice for clarity sake. I guess what I'm wondering is if the difference between the highest and lowest lobes were .021", is this something to be concerned with? I don't know how much space or gap the lifters can make up???

 

[Mike Licht]

that will give you the base circle and the lobe lift combined you need to do it the way I explained to get a real number
Mike

 

[sholdwick]

Lobe differences

Also remember he said he was measureing used cams. There could actualy be that much wear from a poorly broke in cam. 021" on diamter is not really all that much wear. It is only .0105" per side. Which about 3 human hairs. I know, I know lets not get into if it is a red hair or blond or.................