Cam duration @.200" lift

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Cam duration @.200" lift

Post  JBR-3 on April 2nd 2017, 7:49 pm

First let me say that I do understand that there is no substitute for
getting a cam lobe profile readout on a Cam Doctor.

What I'm looking for is sort of a rule-of-thumb to guesstimate the duration at .200" lift
if you know the duration at .050" lift.

For example, on a solid roller I think you can figure that from .002" lift to .050" lift,
you lose about 40-deg to take up ramps, lash, etc. Less on a really fast acting lobe.

So how much duration can you lose going from .050" to .200", another 35~~40 degrees ?
Meaning, if you have 260-deg @.050", you might have 220-deg @ .200" ?

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Re: Cam duration @.200" lift

Post  rmcomprandy on April 2nd 2017, 8:19 pm

There is no rule of thumb ...
that @.200" number can change 15 degrees or more for the same duration @.050" depending upon the aggressiveness of the particular lobe profile.

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Re: Cam duration @.200" lift

Post  Straubtech on April 4th 2017, 12:25 pm

rmcomprandy wrote:There is no rule of thumb ...
that @.200" number can change 15 degrees or more for the same duration @.050" depending upon the aggressiveness of the particular lobe profile.

Agreed. This one reason I tell customers that .050" numbers tell you nothing about the camshaft. It is a reference point selected to "Market" camshafts with. Case in point I have 2 lobes that are .312 and .315 Lobe lift and at .050 they are both 230. Not much difference. Well at .200 there is 14 degrees of difference. One would look at that in .050" numbers and say the one cam is much larger. Well in this case one is much larger. The lobe area is what you need to know. The whole picture.

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Re: Cam duration @.200" lift

Post  JBR-3 on April 4th 2017, 5:18 pm

OK thanks gents.
Did not realize the roller lobes could vary that much.

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Re: Cam duration @.200" lift

Post  68galaxie on April 4th 2017, 5:49 pm

This doesn't apply only to roller lobes, it applies to all lobe types.
The 0.200" duration doesn't tell all about a camshaft either.
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Re: Cam duration @.200" lift

Post  IDT-572 on April 5th 2017, 12:06 pm

.006 numbers play too.............
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Re: Cam duration @.200" lift

Post  Straubtech on April 5th 2017, 12:22 pm

It all matters, but you have to think like an advertiser: what info do we need to sell cams.....needs to be short and sweet. If you put the entire lobe area on there checked at .020" increments you could get 1 lobe per page.

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Re: Cam duration @.200" lift

Post  Lem Evans on April 5th 2017, 10:15 pm

.007" do too.

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