Cam clearance question: interesting test of theory

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Sep 22, 2006 | 11:32 PM

N4cer

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Cam clearance question: interesting test of theory

All you guys who know cams so well:

Everyone says duration hurts PTV clearance... not lift. That has me thinking. I have clearance on this setup that is close. Around 0.050" PTV on the intake side. So let's say that instead of flycutting or changing heads (one of which I'll probably do but let's ignore it for theory's sake), I change to a cam with better exhaust duration and more lift on intake and exhaust. Would that still clear?
I mean, say I went with a cam more like Patrick G's
224/228 .637/.639 110LSA only change it to a 112 or 114+2 LSA?
would I have any issues?

Let's see how this theory pans out.

Sep 23, 2006 | 12:05 AM

ShevrolayZ28

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Here's a great tutorial on valve timing.

http://www.compcams.com/information/tutorials/

Max lift happens when the piston is way down low.

Sep 23, 2006 | 12:28 AM

redtail2426

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depends on how aggresive the lobes are,if they are more aggressive,then you will still lose clearance,and chances are if your adding more lift and keeping the same duration,then its probably a more aggressive lobe,but some customizing could be done i guess.

Sep 23, 2006 | 09:21 AM

Patrick G

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A cam with faster lift off the seat (like an XE-R lobed cam) will help tighten up your p to v clearance, but only a degree or two. Widening the LSA helps because you shorten the overlap cycle, but often that hurts overall performance.

FYI, LSK lobes are not as fast off the seat as XE-R lobes:
49 degrees (.006-.050") for XE-R
50 degrees (.006-.050") for LSK

LSKs are your best choice for p to v help. Solid roller would be better. Now THAT's faster.

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Sep 23, 2006 | 11:47 AM

ShevrolayZ28

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Quote:

Originally Posted by Patrick G

FYI, LSK lobes are not as fast off the seat as XE-R lobes:
49 degrees (.006-.050") for XE-R
50 degrees (.006-.050") for LSK

LSKs are your best choice for p to v help.

I didn't know that. I guess the LSK lobes must have a really fast ramp rate thereafter.

Sep 23, 2006 | 01:10 PM

redtail2426

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yeah i thought the lsk lobes would give you less clearance,this is new and good info to me and im sure lots of other people

Sep 23, 2006 | 01:11 PM

N4cer

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No, I PM'ed Patrick G to get clarity. He's saying that the PTV clearance is even less with the LSKs. So I'm better with my XE-R lobes due to the faster initial ramp rates.