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Old 08-28-2008, 07:27 PM
oldbogie oldbogie is offline
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Quote:
Originally Posted by Morgan22
Can someone educate me of the mechanics of small base circle cams?
What I keep hearing is that they should be avoided like the plague.
Something about harmonics and deflection?
If they are so bad why do they make them?
Since they do what are they intended for?

I have a 351w that I'm going to stroke, 393 and am considering using a small base circle cam to convert to hyd rollers of the stock ford type w/spider.
This is a street motor that won't see past 6K rpm not a high rpm screamer that from what I hear so far is where small base circle cams seem to have a problem with flexing.

Will it work well and be durable?

Thanks.

Morgan
There are a couple problems with small base circle cams.

First, the lobes are sized smaller but the lift over duration remains the same. This places a higher contact load between the lobe and lifter which is a durability and wear issue. A roller is probably a better solution in this case as rollers are better able to absorb larger amounts of contact loading, but like anything else it's not an infinite capability. The flat tappet Ford is probably better able to handle this than the Chevy by virtue of its larger diameter lifter. But I'd still go with a roller given the choice.

Second is related to the first in that the forces on the shaft are greater since the reaction area of the lobe to lifter is less. This increases the torque or twist moments in the shaft. Not a problem with a mild street engine, but when you start getting into high pressure springs especially when combined with high RPMs these factors can arrive at broken cams.

Bogie
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