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Old 07-16-2006, 06:23 PM
xntrik's Avatar
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Cam Question

All engine factors the same, identical lifts, and timed the same at 104* advanced,
what is the difference between these 2 cams?

270 x 270 on a 108* LSA
270 x 280 on a 110.5* LSA

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Old 07-16-2006, 06:49 PM
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this 108*and 110.5* is lobe center separation.the difference is 2.5* .
these numbers are used in cam phasing.why do you ask?

Last edited by nitro_baller4692; 07-16-2006 at 06:55 PM.
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Old 07-17-2006, 10:37 AM
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up to page one
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Old 07-17-2006, 06:21 PM
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i think you mean 4*advanced.yes or no?
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Old 07-17-2006, 08:05 PM
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I know this is a test.

I'm going to try it and show that:
A) I know a little bit
B) I know nothing. (There is that possibility, but I'm doing the test anyway)

I am going to assume that the numbers you gave are duration @ .004" or .006"

I would say that the 270 X 280 would run better on the top because of the longer exhaust duration and even though the LSA is wider the longer exhaust duration gives 2 1/2 degrees more overlap and makes for better scavenging.
I'd say it would sound better than the first cam at the pipes too because of the 7 1/2 degrees more advanced exhaust timing.

I would say that the powerband would be a little wider with the second cam because of the wider LSA.


It looks like a good cam for a smaller motor in a truck.

Unless those numbers you give are duration @ .050"
If that is the case then I doubt you would be pulling a trailer with that motor. Tractor pull weight sled maybe.

Did I get any of that right?


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Last edited by powerrodsmike; 07-17-2006 at 09:22 PM.
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Old 07-19-2006, 03:31 PM
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OK advertised duration...

This is not intended to prove anybody stupid, etc. Just a simple lesson in camshafts.

Think how cams are measured and timed.
Remember the exhaust stroke comes before the intake stroke.
You are on the right track, think it through carefully.

What is the difference between the two cams specified in # 1 ?

It is simple, easy, and confusing.


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Old 07-23-2006, 10:00 AM
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Quote:
Originally Posted by xntrik
All engine factors the same, identical lifts, and timed the same at 104* advanced,
what is the difference between these 2 cams?

270 x 270 on a 108* LSA
270 x 280 on a 110.5* LSA
Nitroballer, you are correct. My addition of the superfluous word "advanced" was incorrect. The intake lobe is centered AFTER Top Dead Center.


The specifed cams and their timing are absolutely identical in every aspect except that the exhaust valve opens 10* sooner. It is termed a nitrous cam.

There are 4 events of importance.
1) intake opening
2) intake closing
3) exhaust opening
4) exhaust closing

Remember that the camshaft turns 1/2 as fast as the crankshaft.
Lobe duration is crankshaft degrees, and LCA/LSA are in camshaft degrees.

******************

"To make this cam function better when the nitrous is on, the exhaust valve might want to be opened 10* earlier. That earlier opening is the only valve event to change in relation to the crank angles involved. But because of the way we quote advance based on LCA, it makes the cam spec look much different.

....we find the cam, with a 10* earlier exhaust opening, is now a 270 x 280 with a 110.5 LCA. If the intake centerline is held in the same place as for the non-nitrous cam at 104*, we find that it is now 6.5* of advance.

....a cam on a wider LCA and plugged in with more advance."

David Vizard, PHR magazine, Aug 2006, p 80, Timing is Everything/ Advance or Retard- What's Needed?

Hope you enjoyed the brain teaser.
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