OK, duration and lift are self explanatory (although advertised duration is confusing).

Lobe separation angle, while I understand the definition, still confounds me.

What are the effects?
Comparing three cams: Each cam has 224/224 duration @.050 and .460 lift. One has LSA of 110, next one 112, next one 114. What characteristics are changed?

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My Elky Page (http://www.geocities.com/chadjlandry/index.html) Updated 7-21-00
"Dive in and get your hands dirty. You'll never know how to do it until you've done it."
Chad Landry
TC Member #643
'68 El Camino

cj,
LSA is what a lot of us used to call overlap. In your example, the 114 cam will idle smoothest and have a broad power band. The 110 will have the choppiest idle and good mid-range, maybe giving up a little on the bottom end. The closer the lobes are together (smaller number), the more overlap, less idle vacuum, rougher idle, etc.

Make any sense?

Tom

OK Chad, I'll start but surely there'll be much more wisdom that I can muster soon...
Whoops, sorry Tom we must've done this simultaneously....

First my observations on advertised duration are that the more aggressive the ramps, the smaller the discrepancy between advertised and measured at 0.050. But its just an observation. But it also makes "mechanical" sense, from a measurement "area under the curve" point of view.

I just had a discussion with a fella named Joe at Crane Cams tech. Very helpful I may add. He indicated that tightening the LSA would shift the power band down the rpm range for a given set of duration measures. to quote exactly, " the power will come on sooner".

So clearly for most street applications, performance wise, the tigher the better. The give up is ( and there's always some compromise) is that I believe a tighter LSA increases low speed reversion, i.e., lope. And consequently will decrease engine vacuum at idle, a bummer for power accesories.

Now Joe and I never spoke of relative power outputs of tight vs. loose LSA's. We were determining the right duration/LSA for my applciation and comparing my solid v a roller. Folks here say tighter LSA makes more power. All I know is that it makes it sooner. And for most applications other than 4500 stall/5.13's, thats good.

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G. Chaas
Gold #62/ACES
67 SS396/(427L88) (http://www.chevelles.com/showroom/chaas1.jpg)

[This message has been edited by Gene Chas (edited 07-25-2000).]

Thanks for the information guys.

So a tighter LSA will cause more overlap, which means the exhaust valve will be "less closed" as the intake valve starts to open?

If I understand this correctly, this overlap will allow the exhaust velocity to "help pull" more air/fuel into the combustion chamber.

Am I right on this, or do I miss the mark completely?

I'm planning to re-cam in the next few months and this is a major factor in my decision.

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My Elky Page (http://www.geocities.com/chadjlandry/index.html) Updated 7-21-00
"Dive in and get your hands dirty. You'll never know how to do it until you've done it."
Chad Landry
TC Member #643
'68 El Camino

Chad, yes, this is precisely my understanding of reversion or "overlap".

EDIT: reversion at low rpm, scavenging at higher rpm.

[This message has been edited by Gene Chas (edited 07-26-2000).]

<BLOCKQUOTE>quote:</font><HR>Originally posted by cjlandry:
Thanks for the information guys.

So a tighter LSA will cause more overlap, which means the exhaust valve will be "less closed" as the intake valve starts to open?

If I understand this correctly, this overlap will allow the exhaust velocity to "help pull" more air/fuel into the combustion chamber.

Am I right on this, or do I miss the mark completely?<HR></BLOCKQUOTE>

This is correct. However, I was under the impression this is called "scavenging." Reversion is gasses being pushed back the way they came. For example, intake gasses being pushed back into the intake manifold.


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Pat Kelley
66 El Camino, daily driver
67 El Camino, STRIP/street
http://cochise.uia.net/pkelley/

Thanks, Gene and Tom. Your explanations were great. I just performed a yahoo search on lobe separation angle and came up with a tutorial (http://www.compcams.com/valvtim1.html) from Competition Cams that may be interesting to others. Check it out. It seems pretty thorough.

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My Elky Page (http://www.geocities.com/chadjlandry/index.html) Updated 7-21-00
"Dive in and get your hands dirty. You'll never know how to do it until you've done it."
Chad Landry
TC Member #643
'68 El Camino