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Old 09-17-2005, 07:54 PM
JPhil JPhil is offline
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Questions for wiped lobe victims & engine gurus

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What were your cam specs (adv. dur., .050 dur., valve lift)?
Was it the intake or exhaust lobe that wiped?

I've been doing some research & figuring...I'm not an experienced engine builder by any means, so if you think I'm barking up the wrong tree, please say so, and why.

I've made a list of a number of cams & specs from a number of manufacturers and used two formulae to try to come up with a "performance vs. reliability" factor. One is ".050 duration divided by valve lift should equal 47.5% or greater" which I saw here (sorry, cannot remember when or who, but thanks). Let's call it the "X factor".
The other is my own creation, "Advertised duration minus .050 duration", or "Y factor".
I realize I do not know where the adv. duration is taken from--.002, .006, or wherever. But that's what's published, that's what I used.

My theory: Both are ways to guage the steepness of the lobe ramp, which determines the stresses on the lifter & lobe, which has an effect on the reliability & longevity of the 'interface'.
Still with me? Here are a few samples:

CAM ADV DUR .050 DUR LIFT X-FCTR Y-FCTR

cr 272H10 272 216 .454 47.6 56
cc HE268H 268 218 .454 48 50
cc XE262H 262/270 218/224 464/470 46.9/47.6 44/46
cc XE268H 268/280 224/230 477/480 46.9/47.9 44/50
lun 60101 256/262 213/219 454/468 46.9/46.8 43/43
chev L82 272/288 224/224 450/460 49.7/48.7 48/64


I know there are other factors to be considered,and with my inexperience I do not necessarily know what they are. But I believe I see a correlation: The the lower the X & Y factors, the lower the reliability....
Does this seem to have any merit? Or is it B.S.?
Comments and thoughts requested and welcomed.

John

well, ding dang it all! I spent a long time getting those numbers into nice neat columns but I can't make 'em stay that way!!! Sorry I guess you all will have to try to sort 'em out. S**t!

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